From d8eabc37310a92df40d07c5a8afc53cebf996716 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 21 Feb 2019 12:36:50 +0100 Subject: x86/msr-index: Cleanup bit defines Greg pointed out that speculation related bit defines are using (1 << N) format instead of BIT(N). Aside of that (1 << N) is wrong as it should use 1UL at least. Clean it up. [ Josh Poimboeuf: Fix tools build ] Reported-by: Greg Kroah-Hartman Signed-off-by: Thomas Gleixner Reviewed-by: Greg Kroah-Hartman Reviewed-by: Borislav Petkov Reviewed-by: Frederic Weisbecker Reviewed-by: Jon Masters Tested-by: Jon Masters --- arch/x86/include/asm/msr-index.h | 34 ++++++++++++++++++---------------- 1 file changed, 18 insertions(+), 16 deletions(-) (limited to 'arch') diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index 8e40c2446fd1..e4074556c37b 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -2,6 +2,8 @@ #ifndef _ASM_X86_MSR_INDEX_H #define _ASM_X86_MSR_INDEX_H +#include + /* * CPU model specific register (MSR) numbers. * @@ -40,14 +42,14 @@ /* Intel MSRs. Some also available on other CPUs */ #define MSR_IA32_SPEC_CTRL 0x00000048 /* Speculation Control */ -#define SPEC_CTRL_IBRS (1 << 0) /* Indirect Branch Restricted Speculation */ +#define SPEC_CTRL_IBRS BIT(0) /* Indirect Branch Restricted Speculation */ #define SPEC_CTRL_STIBP_SHIFT 1 /* Single Thread Indirect Branch Predictor (STIBP) bit */ -#define SPEC_CTRL_STIBP (1 << SPEC_CTRL_STIBP_SHIFT) /* STIBP mask */ +#define SPEC_CTRL_STIBP BIT(SPEC_CTRL_STIBP_SHIFT) /* STIBP mask */ #define SPEC_CTRL_SSBD_SHIFT 2 /* Speculative Store Bypass Disable bit */ -#define SPEC_CTRL_SSBD (1 << SPEC_CTRL_SSBD_SHIFT) /* Speculative Store Bypass Disable */ +#define SPEC_CTRL_SSBD BIT(SPEC_CTRL_SSBD_SHIFT) /* Speculative Store Bypass Disable */ #define MSR_IA32_PRED_CMD 0x00000049 /* Prediction Command */ -#define PRED_CMD_IBPB (1 << 0) /* Indirect Branch Prediction Barrier */ +#define PRED_CMD_IBPB BIT(0) /* Indirect Branch Prediction Barrier */ #define MSR_PPIN_CTL 0x0000004e #define MSR_PPIN 0x0000004f @@ -69,20 +71,20 @@ #define MSR_MTRRcap 0x000000fe #define MSR_IA32_ARCH_CAPABILITIES 0x0000010a -#define ARCH_CAP_RDCL_NO (1 << 0) /* Not susceptible to Meltdown */ -#define ARCH_CAP_IBRS_ALL (1 << 1) /* Enhanced IBRS support */ -#define ARCH_CAP_SKIP_VMENTRY_L1DFLUSH (1 << 3) /* Skip L1D flush on vmentry */ -#define ARCH_CAP_SSB_NO (1 << 4) /* - * Not susceptible to Speculative Store Bypass - * attack, so no Speculative Store Bypass - * control required. - */ +#define ARCH_CAP_RDCL_NO BIT(0) /* Not susceptible to Meltdown */ +#define ARCH_CAP_IBRS_ALL BIT(1) /* Enhanced IBRS support */ +#define ARCH_CAP_SKIP_VMENTRY_L1DFLUSH BIT(3) /* Skip L1D flush on vmentry */ +#define ARCH_CAP_SSB_NO BIT(4) /* + * Not susceptible to Speculative Store Bypass + * attack, so no Speculative Store Bypass + * control required. + */ #define MSR_IA32_FLUSH_CMD 0x0000010b -#define L1D_FLUSH (1 << 0) /* - * Writeback and invalidate the - * L1 data cache. - */ +#define L1D_FLUSH BIT(0) /* + * Writeback and invalidate the + * L1 data cache. + */ #define MSR_IA32_BBL_CR_CTL 0x00000119 #define MSR_IA32_BBL_CR_CTL3 0x0000011e -- cgit v1.2.3 From 36ad35131adacc29b328b9c8b6277a8bf0d6fd5d Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 27 Feb 2019 10:10:23 +0100 Subject: x86/speculation: Consolidate CPU whitelists The CPU vulnerability whitelists have some overlap and there are more whitelists coming along. Use the driver_data field in the x86_cpu_id struct to denote the whitelisted vulnerabilities and combine all whitelists into one. Suggested-by: Linus Torvalds Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Reviewed-by: Greg Kroah-Hartman Reviewed-by: Borislav Petkov Reviewed-by: Jon Masters Tested-by: Jon Masters --- arch/x86/kernel/cpu/common.c | 110 +++++++++++++++++++++++-------------------- 1 file changed, 60 insertions(+), 50 deletions(-) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index cb28e98a0659..26ec15034f86 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -948,61 +948,72 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c) #endif } -static const __initconst struct x86_cpu_id cpu_no_speculation[] = { - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SALTWELL, X86_FEATURE_ANY }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SALTWELL_TABLET, X86_FEATURE_ANY }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_BONNELL_MID, X86_FEATURE_ANY }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SALTWELL_MID, X86_FEATURE_ANY }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_BONNELL, X86_FEATURE_ANY }, - { X86_VENDOR_CENTAUR, 5 }, - { X86_VENDOR_INTEL, 5 }, - { X86_VENDOR_NSC, 5 }, - { X86_VENDOR_ANY, 4 }, +#define NO_SPECULATION BIT(0) +#define NO_MELTDOWN BIT(1) +#define NO_SSB BIT(2) +#define NO_L1TF BIT(3) + +#define VULNWL(_vendor, _family, _model, _whitelist) \ + { X86_VENDOR_##_vendor, _family, _model, X86_FEATURE_ANY, _whitelist } + +#define VULNWL_INTEL(model, whitelist) \ + VULNWL(INTEL, 6, INTEL_FAM6_##model, whitelist) + +#define VULNWL_AMD(family, whitelist) \ + VULNWL(AMD, family, X86_MODEL_ANY, whitelist) + +#define VULNWL_HYGON(family, whitelist) \ + VULNWL(HYGON, family, X86_MODEL_ANY, whitelist) + +static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = { + VULNWL(ANY, 4, X86_MODEL_ANY, NO_SPECULATION), + VULNWL(CENTAUR, 5, X86_MODEL_ANY, NO_SPECULATION), + VULNWL(INTEL, 5, X86_MODEL_ANY, NO_SPECULATION), + VULNWL(NSC, 5, X86_MODEL_ANY, NO_SPECULATION), + + VULNWL_INTEL(ATOM_SALTWELL, NO_SPECULATION), + VULNWL_INTEL(ATOM_SALTWELL_TABLET, NO_SPECULATION), + VULNWL_INTEL(ATOM_SALTWELL_MID, NO_SPECULATION), + VULNWL_INTEL(ATOM_BONNELL, NO_SPECULATION), + VULNWL_INTEL(ATOM_BONNELL_MID, NO_SPECULATION), + + VULNWL_INTEL(ATOM_SILVERMONT, NO_SSB | NO_L1TF), + VULNWL_INTEL(ATOM_SILVERMONT_X, NO_SSB | NO_L1TF), + VULNWL_INTEL(ATOM_SILVERMONT_MID, NO_SSB | NO_L1TF), + VULNWL_INTEL(ATOM_AIRMONT, NO_SSB | NO_L1TF), + VULNWL_INTEL(XEON_PHI_KNL, NO_SSB | NO_L1TF), + VULNWL_INTEL(XEON_PHI_KNM, NO_SSB | NO_L1TF), + + VULNWL_INTEL(CORE_YONAH, NO_SSB), + + VULNWL_INTEL(ATOM_AIRMONT_MID, NO_L1TF), + VULNWL_INTEL(ATOM_GOLDMONT, NO_L1TF), + VULNWL_INTEL(ATOM_GOLDMONT_X, NO_L1TF), + VULNWL_INTEL(ATOM_GOLDMONT_PLUS, NO_L1TF), + + VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF), + VULNWL_AMD(0x10, NO_MELTDOWN | NO_SSB | NO_L1TF), + VULNWL_AMD(0x11, NO_MELTDOWN | NO_SSB | NO_L1TF), + VULNWL_AMD(0x12, NO_MELTDOWN | NO_SSB | NO_L1TF), + + /* FAMILY_ANY must be last, otherwise 0x0f - 0x12 matches won't work */ + VULNWL_AMD(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF), + VULNWL_HYGON(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF), {} }; -static const __initconst struct x86_cpu_id cpu_no_meltdown[] = { - { X86_VENDOR_AMD }, - { X86_VENDOR_HYGON }, - {} -}; - -/* Only list CPUs which speculate but are non susceptible to SSB */ -static const __initconst struct x86_cpu_id cpu_no_spec_store_bypass[] = { - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SILVERMONT }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_AIRMONT }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SILVERMONT_X }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SILVERMONT_MID }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_CORE_YONAH }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_XEON_PHI_KNL }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_XEON_PHI_KNM }, - { X86_VENDOR_AMD, 0x12, }, - { X86_VENDOR_AMD, 0x11, }, - { X86_VENDOR_AMD, 0x10, }, - { X86_VENDOR_AMD, 0xf, }, - {} -}; +static bool __init cpu_matches(unsigned long which) +{ + const struct x86_cpu_id *m = x86_match_cpu(cpu_vuln_whitelist); -static const __initconst struct x86_cpu_id cpu_no_l1tf[] = { - /* in addition to cpu_no_speculation */ - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SILVERMONT }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SILVERMONT_X }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_AIRMONT }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_SILVERMONT_MID }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_AIRMONT_MID }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_GOLDMONT }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_GOLDMONT_X }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_GOLDMONT_PLUS }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_XEON_PHI_KNL }, - { X86_VENDOR_INTEL, 6, INTEL_FAM6_XEON_PHI_KNM }, - {} -}; + return m && !!(m->driver_data & which); +} static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) { u64 ia32_cap = 0; - if (x86_match_cpu(cpu_no_speculation)) + if (cpu_matches(NO_SPECULATION)) return; setup_force_cpu_bug(X86_BUG_SPECTRE_V1); @@ -1011,15 +1022,14 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES)) rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap); - if (!x86_match_cpu(cpu_no_spec_store_bypass) && - !(ia32_cap & ARCH_CAP_SSB_NO) && + if (!cpu_matches(NO_SSB) && !(ia32_cap & ARCH_CAP_SSB_NO) && !cpu_has(c, X86_FEATURE_AMD_SSB_NO)) setup_force_cpu_bug(X86_BUG_SPEC_STORE_BYPASS); if (ia32_cap & ARCH_CAP_IBRS_ALL) setup_force_cpu_cap(X86_FEATURE_IBRS_ENHANCED); - if (x86_match_cpu(cpu_no_meltdown)) + if (cpu_matches(NO_MELTDOWN)) return; /* Rogue Data Cache Load? No! */ @@ -1028,7 +1038,7 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN); - if (x86_match_cpu(cpu_no_l1tf)) + if (cpu_matches(NO_L1TF)) return; setup_force_cpu_bug(X86_BUG_L1TF); -- cgit v1.2.3 From ed5194c2732c8084af9fd159c146ea92bf137128 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Fri, 18 Jan 2019 16:50:16 -0800 Subject: x86/speculation/mds: Add basic bug infrastructure for MDS Microarchitectural Data Sampling (MDS), is a class of side channel attacks on internal buffers in Intel CPUs. The variants are: - Microarchitectural Store Buffer Data Sampling (MSBDS) (CVE-2018-12126) - Microarchitectural Fill Buffer Data Sampling (MFBDS) (CVE-2018-12130) - Microarchitectural Load Port Data Sampling (MLPDS) (CVE-2018-12127) MSBDS leaks Store Buffer Entries which can be speculatively forwarded to a dependent load (store-to-load forwarding) as an optimization. The forward can also happen to a faulting or assisting load operation for a different memory address, which can be exploited under certain conditions. Store buffers are partitioned between Hyper-Threads so cross thread forwarding is not possible. But if a thread enters or exits a sleep state the store buffer is repartitioned which can expose data from one thread to the other. MFBDS leaks Fill Buffer Entries. Fill buffers are used internally to manage L1 miss situations and to hold data which is returned or sent in response to a memory or I/O operation. Fill buffers can forward data to a load operation and also write data to the cache. When the fill buffer is deallocated it can retain the stale data of the preceding operations which can then be forwarded to a faulting or assisting load operation, which can be exploited under certain conditions. Fill buffers are shared between Hyper-Threads so cross thread leakage is possible. MLDPS leaks Load Port Data. Load ports are used to perform load operations from memory or I/O. The received data is then forwarded to the register file or a subsequent operation. In some implementations the Load Port can contain stale data from a previous operation which can be forwarded to faulting or assisting loads under certain conditions, which again can be exploited eventually. Load ports are shared between Hyper-Threads so cross thread leakage is possible. All variants have the same mitigation for single CPU thread case (SMT off), so the kernel can treat them as one MDS issue. Add the basic infrastructure to detect if the current CPU is affected by MDS. [ tglx: Rewrote changelog ] Signed-off-by: Andi Kleen Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Reviewed-by: Greg Kroah-Hartman Reviewed-by: Frederic Weisbecker Reviewed-by: Jon Masters Tested-by: Jon Masters --- arch/x86/include/asm/cpufeatures.h | 2 ++ arch/x86/include/asm/msr-index.h | 5 +++++ arch/x86/kernel/cpu/common.c | 25 ++++++++++++++++--------- 3 files changed, 23 insertions(+), 9 deletions(-) (limited to 'arch') diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index 6d6122524711..ae3f987b24f1 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -344,6 +344,7 @@ /* Intel-defined CPU features, CPUID level 0x00000007:0 (EDX), word 18 */ #define X86_FEATURE_AVX512_4VNNIW (18*32+ 2) /* AVX-512 Neural Network Instructions */ #define X86_FEATURE_AVX512_4FMAPS (18*32+ 3) /* AVX-512 Multiply Accumulation Single precision */ +#define X86_FEATURE_MD_CLEAR (18*32+10) /* VERW clears CPU buffers */ #define X86_FEATURE_PCONFIG (18*32+18) /* Intel PCONFIG */ #define X86_FEATURE_SPEC_CTRL (18*32+26) /* "" Speculation Control (IBRS + IBPB) */ #define X86_FEATURE_INTEL_STIBP (18*32+27) /* "" Single Thread Indirect Branch Predictors */ @@ -381,5 +382,6 @@ #define X86_BUG_SPECTRE_V2 X86_BUG(16) /* CPU is affected by Spectre variant 2 attack with indirect branches */ #define X86_BUG_SPEC_STORE_BYPASS X86_BUG(17) /* CPU is affected by speculative store bypass attack */ #define X86_BUG_L1TF X86_BUG(18) /* CPU is affected by L1 Terminal Fault */ +#define X86_BUG_MDS X86_BUG(19) /* CPU is affected by Microarchitectural data sampling */ #endif /* _ASM_X86_CPUFEATURES_H */ diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index e4074556c37b..e2d30636c03f 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -79,6 +79,11 @@ * attack, so no Speculative Store Bypass * control required. */ +#define ARCH_CAP_MDS_NO BIT(5) /* + * Not susceptible to + * Microarchitectural Data + * Sampling (MDS) vulnerabilities. + */ #define MSR_IA32_FLUSH_CMD 0x0000010b #define L1D_FLUSH BIT(0) /* diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 26ec15034f86..e34817bca504 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -952,6 +952,7 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c) #define NO_MELTDOWN BIT(1) #define NO_SSB BIT(2) #define NO_L1TF BIT(3) +#define NO_MDS BIT(4) #define VULNWL(_vendor, _family, _model, _whitelist) \ { X86_VENDOR_##_vendor, _family, _model, X86_FEATURE_ANY, _whitelist } @@ -971,6 +972,7 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = { VULNWL(INTEL, 5, X86_MODEL_ANY, NO_SPECULATION), VULNWL(NSC, 5, X86_MODEL_ANY, NO_SPECULATION), + /* Intel Family 6 */ VULNWL_INTEL(ATOM_SALTWELL, NO_SPECULATION), VULNWL_INTEL(ATOM_SALTWELL_TABLET, NO_SPECULATION), VULNWL_INTEL(ATOM_SALTWELL_MID, NO_SPECULATION), @@ -987,18 +989,20 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = { VULNWL_INTEL(CORE_YONAH, NO_SSB), VULNWL_INTEL(ATOM_AIRMONT_MID, NO_L1TF), - VULNWL_INTEL(ATOM_GOLDMONT, NO_L1TF), - VULNWL_INTEL(ATOM_GOLDMONT_X, NO_L1TF), - VULNWL_INTEL(ATOM_GOLDMONT_PLUS, NO_L1TF), - VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF), - VULNWL_AMD(0x10, NO_MELTDOWN | NO_SSB | NO_L1TF), - VULNWL_AMD(0x11, NO_MELTDOWN | NO_SSB | NO_L1TF), - VULNWL_AMD(0x12, NO_MELTDOWN | NO_SSB | NO_L1TF), + VULNWL_INTEL(ATOM_GOLDMONT, NO_MDS | NO_L1TF), + VULNWL_INTEL(ATOM_GOLDMONT_X, NO_MDS | NO_L1TF), + VULNWL_INTEL(ATOM_GOLDMONT_PLUS, NO_MDS | NO_L1TF), + + /* AMD Family 0xf - 0x12 */ + VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS), + VULNWL_AMD(0x10, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS), + VULNWL_AMD(0x11, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS), + VULNWL_AMD(0x12, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS), /* FAMILY_ANY must be last, otherwise 0x0f - 0x12 matches won't work */ - VULNWL_AMD(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF), - VULNWL_HYGON(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF), + VULNWL_AMD(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF | NO_MDS), + VULNWL_HYGON(X86_FAMILY_ANY, NO_MELTDOWN | NO_L1TF | NO_MDS), {} }; @@ -1029,6 +1033,9 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) if (ia32_cap & ARCH_CAP_IBRS_ALL) setup_force_cpu_cap(X86_FEATURE_IBRS_ENHANCED); + if (!cpu_matches(NO_MDS) && !(ia32_cap & ARCH_CAP_MDS_NO)) + setup_force_cpu_bug(X86_BUG_MDS); + if (cpu_matches(NO_MELTDOWN)) return; -- cgit v1.2.3 From e261f209c3666e842fd645a1e31f001c3a26def9 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 1 Mar 2019 20:21:08 +0100 Subject: x86/speculation/mds: Add BUG_MSBDS_ONLY This bug bit is set on CPUs which are only affected by Microarchitectural Store Buffer Data Sampling (MSBDS) and not by any other MDS variant. This is important because the Store Buffers are partitioned between Hyper-Threads so cross thread forwarding is not possible. But if a thread enters or exits a sleep state the store buffer is repartitioned which can expose data from one thread to the other. This transition can be mitigated. That means that for CPUs which are only affected by MSBDS SMT can be enabled, if the CPU is not affected by other SMT sensitive vulnerabilities, e.g. L1TF. The XEON PHI variants fall into that category. Also the Silvermont/Airmont ATOMs, but for them it's not really relevant as they do not support SMT, but mark them for completeness sake. Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Reviewed-by: Jon Masters Tested-by: Jon Masters --- arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/kernel/cpu/common.c | 20 ++++++++++++-------- 2 files changed, 13 insertions(+), 8 deletions(-) (limited to 'arch') diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index ae3f987b24f1..bdcea163850a 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -383,5 +383,6 @@ #define X86_BUG_SPEC_STORE_BYPASS X86_BUG(17) /* CPU is affected by speculative store bypass attack */ #define X86_BUG_L1TF X86_BUG(18) /* CPU is affected by L1 Terminal Fault */ #define X86_BUG_MDS X86_BUG(19) /* CPU is affected by Microarchitectural data sampling */ +#define X86_BUG_MSBDS_ONLY X86_BUG(20) /* CPU is only affected by the MSDBS variant of BUG_MDS */ #endif /* _ASM_X86_CPUFEATURES_H */ diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index e34817bca504..132a63dc5a76 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -953,6 +953,7 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c) #define NO_SSB BIT(2) #define NO_L1TF BIT(3) #define NO_MDS BIT(4) +#define MSBDS_ONLY BIT(5) #define VULNWL(_vendor, _family, _model, _whitelist) \ { X86_VENDOR_##_vendor, _family, _model, X86_FEATURE_ANY, _whitelist } @@ -979,16 +980,16 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = { VULNWL_INTEL(ATOM_BONNELL, NO_SPECULATION), VULNWL_INTEL(ATOM_BONNELL_MID, NO_SPECULATION), - VULNWL_INTEL(ATOM_SILVERMONT, NO_SSB | NO_L1TF), - VULNWL_INTEL(ATOM_SILVERMONT_X, NO_SSB | NO_L1TF), - VULNWL_INTEL(ATOM_SILVERMONT_MID, NO_SSB | NO_L1TF), - VULNWL_INTEL(ATOM_AIRMONT, NO_SSB | NO_L1TF), - VULNWL_INTEL(XEON_PHI_KNL, NO_SSB | NO_L1TF), - VULNWL_INTEL(XEON_PHI_KNM, NO_SSB | NO_L1TF), + VULNWL_INTEL(ATOM_SILVERMONT, NO_SSB | NO_L1TF | MSBDS_ONLY), + VULNWL_INTEL(ATOM_SILVERMONT_X, NO_SSB | NO_L1TF | MSBDS_ONLY), + VULNWL_INTEL(ATOM_SILVERMONT_MID, NO_SSB | NO_L1TF | MSBDS_ONLY), + VULNWL_INTEL(ATOM_AIRMONT, NO_SSB | NO_L1TF | MSBDS_ONLY), + VULNWL_INTEL(XEON_PHI_KNL, NO_SSB | NO_L1TF | MSBDS_ONLY), + VULNWL_INTEL(XEON_PHI_KNM, NO_SSB | NO_L1TF | MSBDS_ONLY), VULNWL_INTEL(CORE_YONAH, NO_SSB), - VULNWL_INTEL(ATOM_AIRMONT_MID, NO_L1TF), + VULNWL_INTEL(ATOM_AIRMONT_MID, NO_L1TF | MSBDS_ONLY), VULNWL_INTEL(ATOM_GOLDMONT, NO_MDS | NO_L1TF), VULNWL_INTEL(ATOM_GOLDMONT_X, NO_MDS | NO_L1TF), @@ -1033,8 +1034,11 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c) if (ia32_cap & ARCH_CAP_IBRS_ALL) setup_force_cpu_cap(X86_FEATURE_IBRS_ENHANCED); - if (!cpu_matches(NO_MDS) && !(ia32_cap & ARCH_CAP_MDS_NO)) + if (!cpu_matches(NO_MDS) && !(ia32_cap & ARCH_CAP_MDS_NO)) { setup_force_cpu_bug(X86_BUG_MDS); + if (cpu_matches(MSBDS_ONLY)) + setup_force_cpu_bug(X86_BUG_MSBDS_ONLY); + } if (cpu_matches(NO_MELTDOWN)) return; -- cgit v1.2.3 From 6c4dbbd14730c43f4ed808a9c42ca41625925c22 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Fri, 18 Jan 2019 16:50:23 -0800 Subject: x86/kvm: Expose X86_FEATURE_MD_CLEAR to guests X86_FEATURE_MD_CLEAR is a new CPUID bit which is set when microcode provides the mechanism to invoke a flush of various exploitable CPU buffers by invoking the VERW instruction. Hand it through to guests so they can adjust their mitigations. This also requires corresponding qemu changes, which are available separately. [ tglx: Massaged changelog ] Signed-off-by: Andi Kleen Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Reviewed-by: Greg Kroah-Hartman Reviewed-by: Frederic Weisbecker Reviewed-by: Jon Masters Tested-by: Jon Masters --- arch/x86/kvm/cpuid.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index c07958b59f50..39501e7afdb4 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -410,7 +410,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, /* cpuid 7.0.edx*/ const u32 kvm_cpuid_7_0_edx_x86_features = F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) | - F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP); + F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP) | + F(MD_CLEAR); /* all calls to cpuid_count() should be made on the same cpu */ get_cpu(); -- cgit v1.2.3 From 6a9e529272517755904b7afa639f6db59ddb793e Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 18 Feb 2019 23:13:06 +0100 Subject: x86/speculation/mds: Add mds_clear_cpu_buffers() The Microarchitectural Data Sampling (MDS) vulernabilities are mitigated by clearing the affected CPU buffers. The mechanism for clearing the buffers uses the unused and obsolete VERW instruction in combination with a microcode update which triggers a CPU buffer clear when VERW is executed. Provide a inline function with the assembly magic. The argument of the VERW instruction must be a memory operand as documented: "MD_CLEAR enumerates that the memory-operand variant of VERW (for example, VERW m16) has been extended to also overwrite buffers affected by MDS. This buffer overwriting functionality is not guaranteed for the register operand variant of VERW." Documentation also recommends to use a writable data segment selector: "The buffer overwriting occurs regardless of the result of the VERW permission check, as well as when the selector is null or causes a descriptor load segment violation. However, for lowest latency we recommend using a selector that indicates a valid writable data segment." Add x86 specific documentation about MDS and the internal workings of the mitigation. Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Reviewed-by: Greg Kroah-Hartman Reviewed-by: Frederic Weisbecker Reviewed-by: Jon Masters Tested-by: Jon Masters --- Documentation/index.rst | 1 + Documentation/x86/conf.py | 10 ++++ Documentation/x86/index.rst | 8 +++ Documentation/x86/mds.rst | 99 ++++++++++++++++++++++++++++++++++++ arch/x86/include/asm/nospec-branch.h | 25 +++++++++ 5 files changed, 143 insertions(+) create mode 100644 Documentation/x86/conf.py create mode 100644 Documentation/x86/index.rst create mode 100644 Documentation/x86/mds.rst (limited to 'arch') diff --git a/Documentation/index.rst b/Documentation/index.rst index c858c2e66e36..63864826dcd6 100644 --- a/Documentation/index.rst +++ b/Documentation/index.rst @@ -101,6 +101,7 @@ implementation. :maxdepth: 2 sh/index + x86/index Filesystem Documentation ------------------------ diff --git a/Documentation/x86/conf.py b/Documentation/x86/conf.py new file mode 100644 index 000000000000..33c5c3142e20 --- /dev/null +++ b/Documentation/x86/conf.py @@ -0,0 +1,10 @@ +# -*- coding: utf-8; mode: python -*- + +project = "X86 architecture specific documentation" + +tags.add("subproject") + +latex_documents = [ + ('index', 'x86.tex', project, + 'The kernel development community', 'manual'), +] diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst new file mode 100644 index 000000000000..ef389dcf1b1d --- /dev/null +++ b/Documentation/x86/index.rst @@ -0,0 +1,8 @@ +========================== +x86 architecture specifics +========================== + +.. toctree:: + :maxdepth: 1 + + mds diff --git a/Documentation/x86/mds.rst b/Documentation/x86/mds.rst new file mode 100644 index 000000000000..1096738d50f2 --- /dev/null +++ b/Documentation/x86/mds.rst @@ -0,0 +1,99 @@ +Microarchitectural Data Sampling (MDS) mitigation +================================================= + +.. _mds: + +Overview +-------- + +Microarchitectural Data Sampling (MDS) is a family of side channel attacks +on internal buffers in Intel CPUs. The variants are: + + - Microarchitectural Store Buffer Data Sampling (MSBDS) (CVE-2018-12126) + - Microarchitectural Fill Buffer Data Sampling (MFBDS) (CVE-2018-12130) + - Microarchitectural Load Port Data Sampling (MLPDS) (CVE-2018-12127) + +MSBDS leaks Store Buffer Entries which can be speculatively forwarded to a +dependent load (store-to-load forwarding) as an optimization. The forward +can also happen to a faulting or assisting load operation for a different +memory address, which can be exploited under certain conditions. Store +buffers are partitioned between Hyper-Threads so cross thread forwarding is +not possible. But if a thread enters or exits a sleep state the store +buffer is repartitioned which can expose data from one thread to the other. + +MFBDS leaks Fill Buffer Entries. Fill buffers are used internally to manage +L1 miss situations and to hold data which is returned or sent in response +to a memory or I/O operation. Fill buffers can forward data to a load +operation and also write data to the cache. When the fill buffer is +deallocated it can retain the stale data of the preceding operations which +can then be forwarded to a faulting or assisting load operation, which can +be exploited under certain conditions. Fill buffers are shared between +Hyper-Threads so cross thread leakage is possible. + +MLPDS leaks Load Port Data. Load ports are used to perform load operations +from memory or I/O. The received data is then forwarded to the register +file or a subsequent operation. In some implementations the Load Port can +contain stale data from a previous operation which can be forwarded to +faulting or assisting loads under certain conditions, which again can be +exploited eventually. Load ports are shared between Hyper-Threads so cross +thread leakage is possible. + + +Exposure assumptions +-------------------- + +It is assumed that attack code resides in user space or in a guest with one +exception. The rationale behind this assumption is that the code construct +needed for exploiting MDS requires: + + - to control the load to trigger a fault or assist + + - to have a disclosure gadget which exposes the speculatively accessed + data for consumption through a side channel. + + - to control the pointer through which the disclosure gadget exposes the + data + +The existence of such a construct in the kernel cannot be excluded with +100% certainty, but the complexity involved makes it extremly unlikely. + +There is one exception, which is untrusted BPF. The functionality of +untrusted BPF is limited, but it needs to be thoroughly investigated +whether it can be used to create such a construct. + + +Mitigation strategy +------------------- + +All variants have the same mitigation strategy at least for the single CPU +thread case (SMT off): Force the CPU to clear the affected buffers. + +This is achieved by using the otherwise unused and obsolete VERW +instruction in combination with a microcode update. The microcode clears +the affected CPU buffers when the VERW instruction is executed. + +For virtualization there are two ways to achieve CPU buffer +clearing. Either the modified VERW instruction or via the L1D Flush +command. The latter is issued when L1TF mitigation is enabled so the extra +VERW can be avoided. If the CPU is not affected by L1TF then VERW needs to +be issued. + +If the VERW instruction with the supplied segment selector argument is +executed on a CPU without the microcode update there is no side effect +other than a small number of pointlessly wasted CPU cycles. + +This does not protect against cross Hyper-Thread attacks except for MSBDS +which is only exploitable cross Hyper-thread when one of the Hyper-Threads +enters a C-state. + +The kernel provides a function to invoke the buffer clearing: + + mds_clear_cpu_buffers() + +The mitigation is invoked on kernel/userspace, hypervisor/guest and C-state +(idle) transitions. + +According to current knowledge additional mitigations inside the kernel +itself are not required because the necessary gadgets to expose the leaked +data cannot be controlled in a way which allows exploitation from malicious +user space or VM guests. diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index dad12b767ba0..67cb9b2082b1 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -318,6 +318,31 @@ DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp); DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb); +#include + +/** + * mds_clear_cpu_buffers - Mitigation for MDS vulnerability + * + * This uses the otherwise unused and obsolete VERW instruction in + * combination with microcode which triggers a CPU buffer flush when the + * instruction is executed. + */ +static inline void mds_clear_cpu_buffers(void) +{ + static const u16 ds = __KERNEL_DS; + + /* + * Has to be the memory-operand variant because only that + * guarantees the CPU buffer flush functionality according to + * documentation. The register-operand variant does not. + * Works with any segment selector, but a valid writable + * data segment is the fastest variant. + * + * "cc" clobber is required because VERW modifies ZF. + */ + asm volatile("verw %[ds]" : : [ds] "m" (ds) : "cc"); +} + #endif /* __ASSEMBLY__ */ /* -- cgit v1.2.3 From 04dcbdb8057827b043b3c71aa397c4c63e67d086 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 18 Feb 2019 23:42:51 +0100 Subject: x86/speculation/mds: Clear CPU buffers on exit to user Add a static key which controls the invocation of the CPU buffer clear mechanism on exit to user space and add the call into prepare_exit_to_usermode() and do_nmi() right before actually returning. Add documentation which kernel to user space transition this covers and explain why some corner cases are not mitigated. Signed-off-by: Thomas Gleixner Reviewed-by: Greg Kroah-Hartman Reviewed-by: Borislav Petkov Reviewed-by: Frederic Weisbecker Reviewed-by: Jon Masters Tested-by: Jon Masters --- Documentation/x86/mds.rst | 52 ++++++++++++++++++++++++++++++++++++ arch/x86/entry/common.c | 3 +++ arch/x86/include/asm/nospec-branch.h | 13 +++++++++ arch/x86/kernel/cpu/bugs.c | 3 +++ arch/x86/kernel/nmi.c | 4 +++ arch/x86/kernel/traps.c | 8 ++++++ 6 files changed, 83 insertions(+) (limited to 'arch') diff --git a/Documentation/x86/mds.rst b/Documentation/x86/mds.rst index 1096738d50f2..54d935bf283b 100644 --- a/Documentation/x86/mds.rst +++ b/Documentation/x86/mds.rst @@ -97,3 +97,55 @@ According to current knowledge additional mitigations inside the kernel itself are not required because the necessary gadgets to expose the leaked data cannot be controlled in a way which allows exploitation from malicious user space or VM guests. + +Mitigation points +----------------- + +1. Return to user space +^^^^^^^^^^^^^^^^^^^^^^^ + + When transitioning from kernel to user space the CPU buffers are flushed + on affected CPUs when the mitigation is not disabled on the kernel + command line. The migitation is enabled through the static key + mds_user_clear. + + The mitigation is invoked in prepare_exit_to_usermode() which covers + most of the kernel to user space transitions. There are a few exceptions + which are not invoking prepare_exit_to_usermode() on return to user + space. These exceptions use the paranoid exit code. + + - Non Maskable Interrupt (NMI): + + Access to sensible data like keys, credentials in the NMI context is + mostly theoretical: The CPU can do prefetching or execute a + misspeculated code path and thereby fetching data which might end up + leaking through a buffer. + + But for mounting other attacks the kernel stack address of the task is + already valuable information. So in full mitigation mode, the NMI is + mitigated on the return from do_nmi() to provide almost complete + coverage. + + - Double fault (#DF): + + A double fault is usually fatal, but the ESPFIX workaround, which can + be triggered from user space through modify_ldt(2) is a recoverable + double fault. #DF uses the paranoid exit path, so explicit mitigation + in the double fault handler is required. + + - Machine Check Exception (#MC): + + Another corner case is a #MC which hits between the CPU buffer clear + invocation and the actual return to user. As this still is in kernel + space it takes the paranoid exit path which does not clear the CPU + buffers. So the #MC handler repopulates the buffers to some + extent. Machine checks are not reliably controllable and the window is + extremly small so mitigation would just tick a checkbox that this + theoretical corner case is covered. To keep the amount of special + cases small, ignore #MC. + + - Debug Exception (#DB): + + This takes the paranoid exit path only when the INT1 breakpoint is in + kernel space. #DB on a user space address takes the regular exit path, + so no extra mitigation required. diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 7bc105f47d21..19f650d729f5 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -31,6 +31,7 @@ #include #include #include +#include #define CREATE_TRACE_POINTS #include @@ -212,6 +213,8 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) #endif user_enter_irqoff(); + + mds_user_clear_cpu_buffers(); } #define SYSCALL_EXIT_WORK_FLAGS \ diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 67cb9b2082b1..65b747286d96 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -318,6 +318,8 @@ DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp); DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb); +DECLARE_STATIC_KEY_FALSE(mds_user_clear); + #include /** @@ -343,6 +345,17 @@ static inline void mds_clear_cpu_buffers(void) asm volatile("verw %[ds]" : : [ds] "m" (ds) : "cc"); } +/** + * mds_user_clear_cpu_buffers - Mitigation for MDS vulnerability + * + * Clear CPU buffers if the corresponding static key is enabled + */ +static inline void mds_user_clear_cpu_buffers(void) +{ + if (static_branch_likely(&mds_user_clear)) + mds_clear_cpu_buffers(); +} + #endif /* __ASSEMBLY__ */ /* diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 01874d54f4fd..dbb45014de1b 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -63,6 +63,9 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); /* Control unconditional IBPB in switch_mm() */ DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb); +/* Control MDS CPU buffer clear before returning to user space */ +DEFINE_STATIC_KEY_FALSE(mds_user_clear); + void __init check_bugs(void) { identify_boot_cpu(); diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index 18bc9b51ac9b..086cf1d1d71d 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -34,6 +34,7 @@ #include #include #include +#include #define CREATE_TRACE_POINTS #include @@ -533,6 +534,9 @@ nmi_restart: write_cr2(this_cpu_read(nmi_cr2)); if (this_cpu_dec_return(nmi_state)) goto nmi_restart; + + if (user_mode(regs)) + mds_user_clear_cpu_buffers(); } NOKPROBE_SYMBOL(do_nmi); diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 9b7c4ca8f0a7..85fe1870f873 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -58,6 +58,7 @@ #include #include #include +#include #include #include #include @@ -366,6 +367,13 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code) regs->ip = (unsigned long)general_protection; regs->sp = (unsigned long)&gpregs->orig_ax; + /* + * This situation can be triggered by userspace via + * modify_ldt(2) and the return does not take the regular + * user space exit, so a CPU buffer clear is required when + * MDS mitigation is enabled. + */ + mds_user_clear_cpu_buffers(); return; } #endif -- cgit v1.2.3 From 650b68a0622f933444a6d66936abb3103029413b Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 27 Feb 2019 12:48:14 +0100 Subject: x86/kvm/vmx: Add MDS protection when L1D Flush is not active CPUs which are affected by L1TF and MDS mitigate MDS with the L1D Flush on VMENTER when updated microcode is installed. If a CPU is not affected by L1TF or if the L1D Flush is not in use, then MDS mitigation needs to be invoked explicitly. For these cases, follow the host mitigation state and invoke the MDS mitigation before VMENTER. Signed-off-by: Thomas Gleixner Reviewed-by: Greg Kroah-Hartman Reviewed-by: Frederic Weisbecker Reviewed-by: Borislav Petkov Reviewed-by: Jon Masters Tested-by: Jon Masters --- arch/x86/kernel/cpu/bugs.c | 1 + arch/x86/kvm/vmx/vmx.c | 3 +++ 2 files changed, 4 insertions(+) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index dbb45014de1b..29ed8e8dfee2 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -65,6 +65,7 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb); /* Control MDS CPU buffer clear before returning to user space */ DEFINE_STATIC_KEY_FALSE(mds_user_clear); +EXPORT_SYMBOL_GPL(mds_user_clear); void __init check_bugs(void) { diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 30a6bcd735ec..544bd24a9c1e 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6369,8 +6369,11 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx) evmcs_rsp = static_branch_unlikely(&enable_evmcs) ? (unsigned long)¤t_evmcs->host_rsp : 0; + /* L1D Flush includes CPU buffer clear to mitigate MDS */ if (static_branch_unlikely(&vmx_l1d_should_flush)) vmx_l1d_flush(vcpu); + else if (static_branch_unlikely(&mds_user_clear)) + mds_clear_cpu_buffers(); asm( /* Store host registers */ -- cgit v1.2.3 From 07f07f55a29cb705e221eda7894dd67ab81ef343 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 18 Feb 2019 23:04:01 +0100 Subject: x86/speculation/mds: Conditionally clear CPU buffers on idle entry Add a static key which controls the invocation of the CPU buffer clear mechanism on idle entry. This is independent of other MDS mitigations because the idle entry invocation to mitigate the potential leakage due to store buffer repartitioning is only necessary on SMT systems. Add the actual invocations to the different halt/mwait variants which covers all usage sites. mwaitx is not patched as it's not available on Intel CPUs. The buffer clear is only invoked before entering the C-State to prevent that stale data from the idling CPU is spilled to the Hyper-Thread sibling after the Store buffer got repartitioned and all entries are available to the non idle sibling. When coming out of idle the store buffer is partitioned again so each sibling has half of it available. Now CPU which returned from idle could be speculatively exposed to contents of the sibling, but the buffers are flushed either on exit to user space or on VMENTER. When later on conditional buffer clearing is implemented on top of this, then there is no action required either because before returning to user space the context switch will set the condition flag which causes a flush on the return to user path. Note, that the buffer clearing on idle is only sensible on CPUs which are solely affected by MSBDS and not any other variant of MDS because the other MDS variants cannot be mitigated when SMT is enabled, so the buffer clearing on idle would be a window dressing exercise. This intentionally does not handle the case in the acpi/processor_idle driver which uses the legacy IO port interface for C-State transitions for two reasons: - The acpi/processor_idle driver was replaced by the intel_idle driver almost a decade ago. Anything Nehalem upwards supports it and defaults to that new driver. - The legacy IO port interface is likely to be used on older and therefore unaffected CPUs or on systems which do not receive microcode updates anymore, so there is no point in adding that. Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Reviewed-by: Greg Kroah-Hartman Reviewed-by: Frederic Weisbecker Reviewed-by: Jon Masters Tested-by: Jon Masters --- Documentation/x86/mds.rst | 42 ++++++++++++++++++++++++++++++++++++ arch/x86/include/asm/irqflags.h | 4 ++++ arch/x86/include/asm/mwait.h | 7 ++++++ arch/x86/include/asm/nospec-branch.h | 12 +++++++++++ arch/x86/kernel/cpu/bugs.c | 3 +++ 5 files changed, 68 insertions(+) (limited to 'arch') diff --git a/Documentation/x86/mds.rst b/Documentation/x86/mds.rst index 54d935bf283b..87ce8ac9f36e 100644 --- a/Documentation/x86/mds.rst +++ b/Documentation/x86/mds.rst @@ -149,3 +149,45 @@ Mitigation points This takes the paranoid exit path only when the INT1 breakpoint is in kernel space. #DB on a user space address takes the regular exit path, so no extra mitigation required. + + +2. C-State transition +^^^^^^^^^^^^^^^^^^^^^ + + When a CPU goes idle and enters a C-State the CPU buffers need to be + cleared on affected CPUs when SMT is active. This addresses the + repartitioning of the store buffer when one of the Hyper-Threads enters + a C-State. + + When SMT is inactive, i.e. either the CPU does not support it or all + sibling threads are offline CPU buffer clearing is not required. + + The idle clearing is enabled on CPUs which are only affected by MSBDS + and not by any other MDS variant. The other MDS variants cannot be + protected against cross Hyper-Thread attacks because the Fill Buffer and + the Load Ports are shared. So on CPUs affected by other variants, the + idle clearing would be a window dressing exercise and is therefore not + activated. + + The invocation is controlled by the static key mds_idle_clear which is + switched depending on the chosen mitigation mode and the SMT state of + the system. + + The buffer clear is only invoked before entering the C-State to prevent + that stale data from the idling CPU from spilling to the Hyper-Thread + sibling after the store buffer got repartitioned and all entries are + available to the non idle sibling. + + When coming out of idle the store buffer is partitioned again so each + sibling has half of it available. The back from idle CPU could be then + speculatively exposed to contents of the sibling. The buffers are + flushed either on exit to user space or on VMENTER so malicious code + in user space or the guest cannot speculatively access them. + + The mitigation is hooked into all variants of halt()/mwait(), but does + not cover the legacy ACPI IO-Port mechanism because the ACPI idle driver + has been superseded by the intel_idle driver around 2010 and is + preferred on all affected CPUs which are expected to gain the MD_CLEAR + functionality in microcode. Aside of that the IO-Port mechanism is a + legacy interface which is only used on older systems which are either + not affected or do not receive microcode updates anymore. diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h index 058e40fed167..8a0e56e1dcc9 100644 --- a/arch/x86/include/asm/irqflags.h +++ b/arch/x86/include/asm/irqflags.h @@ -6,6 +6,8 @@ #ifndef __ASSEMBLY__ +#include + /* Provide __cpuidle; we can't safely include */ #define __cpuidle __attribute__((__section__(".cpuidle.text"))) @@ -54,11 +56,13 @@ static inline void native_irq_enable(void) static inline __cpuidle void native_safe_halt(void) { + mds_idle_clear_cpu_buffers(); asm volatile("sti; hlt": : :"memory"); } static inline __cpuidle void native_halt(void) { + mds_idle_clear_cpu_buffers(); asm volatile("hlt": : :"memory"); } diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h index 39a2fb29378a..eb0f80ce8524 100644 --- a/arch/x86/include/asm/mwait.h +++ b/arch/x86/include/asm/mwait.h @@ -6,6 +6,7 @@ #include #include +#include #define MWAIT_SUBSTATE_MASK 0xf #define MWAIT_CSTATE_MASK 0xf @@ -40,6 +41,8 @@ static inline void __monitorx(const void *eax, unsigned long ecx, static inline void __mwait(unsigned long eax, unsigned long ecx) { + mds_idle_clear_cpu_buffers(); + /* "mwait %eax, %ecx;" */ asm volatile(".byte 0x0f, 0x01, 0xc9;" :: "a" (eax), "c" (ecx)); @@ -74,6 +77,8 @@ static inline void __mwait(unsigned long eax, unsigned long ecx) static inline void __mwaitx(unsigned long eax, unsigned long ebx, unsigned long ecx) { + /* No MDS buffer clear as this is AMD/HYGON only */ + /* "mwaitx %eax, %ebx, %ecx;" */ asm volatile(".byte 0x0f, 0x01, 0xfb;" :: "a" (eax), "b" (ebx), "c" (ecx)); @@ -81,6 +86,8 @@ static inline void __mwaitx(unsigned long eax, unsigned long ebx, static inline void __sti_mwait(unsigned long eax, unsigned long ecx) { + mds_idle_clear_cpu_buffers(); + trace_hardirqs_on(); /* "mwait %eax, %ecx;" */ asm volatile("sti; .byte 0x0f, 0x01, 0xc9;" diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 65b747286d96..4e970390110f 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -319,6 +319,7 @@ DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb); DECLARE_STATIC_KEY_FALSE(mds_user_clear); +DECLARE_STATIC_KEY_FALSE(mds_idle_clear); #include @@ -356,6 +357,17 @@ static inline void mds_user_clear_cpu_buffers(void) mds_clear_cpu_buffers(); } +/** + * mds_idle_clear_cpu_buffers - Mitigation for MDS vulnerability + * + * Clear CPU buffers if the corresponding static key is enabled + */ +static inline void mds_idle_clear_cpu_buffers(void) +{ + if (static_branch_likely(&mds_idle_clear)) + mds_clear_cpu_buffers(); +} + #endif /* __ASSEMBLY__ */ /* diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 29ed8e8dfee2..916995167301 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -66,6 +66,9 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb); /* Control MDS CPU buffer clear before returning to user space */ DEFINE_STATIC_KEY_FALSE(mds_user_clear); EXPORT_SYMBOL_GPL(mds_user_clear); +/* Control MDS CPU buffer clear before idling (halt, mwait) */ +DEFINE_STATIC_KEY_FALSE(mds_idle_clear); +EXPORT_SYMBOL_GPL(mds_idle_clear); void __init check_bugs(void) { -- cgit v1.2.3 From bc1241700acd82ec69fde98c5763ce51086269f8 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 18 Feb 2019 22:04:08 +0100 Subject: x86/speculation/mds: Add mitigation control for MDS Now that the mitigations are in place, add a command line parameter to control the mitigation, a mitigation selector function and a SMT update mechanism. This is the minimal straight forward initial implementation which just provides an always on/off mode. The command line parameter is: mds=[full|off] This is consistent with the existing mitigations for other speculative hardware vulnerabilities. The idle invocation is dynamically updated according to the SMT state of the system similar to the dynamic update of the STIBP mitigation. The idle mitigation is limited to CPUs which are only affected by MSBDS and not any other variant, because the other variants cannot be mitigated on SMT enabled systems. Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Reviewed-by: Jon Masters Tested-by: Jon Masters --- Documentation/admin-guide/kernel-parameters.txt | 22 ++++++++ arch/x86/include/asm/processor.h | 5 ++ arch/x86/kernel/cpu/bugs.c | 70 +++++++++++++++++++++++++ 3 files changed, 97 insertions(+) (limited to 'arch') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 858b6c0b9a15..dddb024eb523 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2356,6 +2356,28 @@ Format: , Specifies range of consoles to be captured by the MDA. + mds= [X86,INTEL] + Control mitigation for the Micro-architectural Data + Sampling (MDS) vulnerability. + + Certain CPUs are vulnerable to an exploit against CPU + internal buffers which can forward information to a + disclosure gadget under certain conditions. + + In vulnerable processors, the speculatively + forwarded data can be used in a cache side channel + attack, to access data to which the attacker does + not have direct access. + + This parameter controls the MDS mitigation. The + options are: + + full - Enable MDS mitigation on vulnerable CPUs + off - Unconditionally disable MDS mitigation + + Not specifying this option is equivalent to + mds=full. + mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory Amount of memory to be used when the kernel is not able to see the whole system memory or for test. diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 33051436c864..1f0295783325 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -992,4 +992,9 @@ enum l1tf_mitigations { extern enum l1tf_mitigations l1tf_mitigation; +enum mds_mitigations { + MDS_MITIGATION_OFF, + MDS_MITIGATION_FULL, +}; + #endif /* _ASM_X86_PROCESSOR_H */ diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 916995167301..c7b29d200d27 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -37,6 +37,7 @@ static void __init spectre_v2_select_mitigation(void); static void __init ssb_select_mitigation(void); static void __init l1tf_select_mitigation(void); +static void __init mds_select_mitigation(void); /* The base value of the SPEC_CTRL MSR that always has to be preserved. */ u64 x86_spec_ctrl_base; @@ -108,6 +109,8 @@ void __init check_bugs(void) l1tf_select_mitigation(); + mds_select_mitigation(); + #ifdef CONFIG_X86_32 /* * Check whether we are able to run this kernel safely on SMP. @@ -213,6 +216,50 @@ static void x86_amd_ssb_disable(void) wrmsrl(MSR_AMD64_LS_CFG, msrval); } +#undef pr_fmt +#define pr_fmt(fmt) "MDS: " fmt + +/* Default mitigation for L1TF-affected CPUs */ +static enum mds_mitigations mds_mitigation __ro_after_init = MDS_MITIGATION_FULL; + +static const char * const mds_strings[] = { + [MDS_MITIGATION_OFF] = "Vulnerable", + [MDS_MITIGATION_FULL] = "Mitigation: Clear CPU buffers" +}; + +static void __init mds_select_mitigation(void) +{ + if (!boot_cpu_has_bug(X86_BUG_MDS)) { + mds_mitigation = MDS_MITIGATION_OFF; + return; + } + + if (mds_mitigation == MDS_MITIGATION_FULL) { + if (boot_cpu_has(X86_FEATURE_MD_CLEAR)) + static_branch_enable(&mds_user_clear); + else + mds_mitigation = MDS_MITIGATION_OFF; + } + pr_info("%s\n", mds_strings[mds_mitigation]); +} + +static int __init mds_cmdline(char *str) +{ + if (!boot_cpu_has_bug(X86_BUG_MDS)) + return 0; + + if (!str) + return -EINVAL; + + if (!strcmp(str, "off")) + mds_mitigation = MDS_MITIGATION_OFF; + else if (!strcmp(str, "full")) + mds_mitigation = MDS_MITIGATION_FULL; + + return 0; +} +early_param("mds", mds_cmdline); + #undef pr_fmt #define pr_fmt(fmt) "Spectre V2 : " fmt @@ -617,6 +664,26 @@ static void update_indir_branch_cond(void) static_branch_disable(&switch_to_cond_stibp); } +/* Update the static key controlling the MDS CPU buffer clear in idle */ +static void update_mds_branch_idle(void) +{ + /* + * Enable the idle clearing if SMT is active on CPUs which are + * affected only by MSBDS and not any other MDS variant. + * + * The other variants cannot be mitigated when SMT is enabled, so + * clearing the buffers on idle just to prevent the Store Buffer + * repartitioning leak would be a window dressing exercise. + */ + if (!boot_cpu_has_bug(X86_BUG_MSBDS_ONLY)) + return; + + if (sched_smt_active()) + static_branch_enable(&mds_idle_clear); + else + static_branch_disable(&mds_idle_clear); +} + void arch_smt_update(void) { /* Enhanced IBRS implies STIBP. No update required. */ @@ -638,6 +705,9 @@ void arch_smt_update(void) break; } + if (mds_mitigation == MDS_MITIGATION_FULL) + update_mds_branch_idle(); + mutex_unlock(&spec_ctrl_mutex); } -- cgit v1.2.3 From 8a4b06d391b0a42a373808979b5028f5c84d9c6a Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 18 Feb 2019 22:51:43 +0100 Subject: x86/speculation/mds: Add sysfs reporting for MDS Add the sysfs reporting file for MDS. It exposes the vulnerability and mitigation state similar to the existing files for the other speculative hardware vulnerabilities. Signed-off-by: Thomas Gleixner Reviewed-by: Greg Kroah-Hartman Reviewed-by: Borislav Petkov Reviewed-by: Jon Masters Tested-by: Jon Masters --- Documentation/ABI/testing/sysfs-devices-system-cpu | 1 + arch/x86/kernel/cpu/bugs.c | 25 ++++++++++++++++++++++ drivers/base/cpu.c | 8 +++++++ include/linux/cpu.h | 2 ++ 4 files changed, 36 insertions(+) (limited to 'arch') diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 9605dbd4b5b5..2db5c3407fd6 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -484,6 +484,7 @@ What: /sys/devices/system/cpu/vulnerabilities /sys/devices/system/cpu/vulnerabilities/spectre_v2 /sys/devices/system/cpu/vulnerabilities/spec_store_bypass /sys/devices/system/cpu/vulnerabilities/l1tf + /sys/devices/system/cpu/vulnerabilities/mds Date: January 2018 Contact: Linux kernel mailing list Description: Information about CPU vulnerabilities diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index c7b29d200d27..7ab16a6ed064 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1172,6 +1172,22 @@ static ssize_t l1tf_show_state(char *buf) } #endif +static ssize_t mds_show_state(char *buf) +{ + if (!hypervisor_is_type(X86_HYPER_NATIVE)) { + return sprintf(buf, "%s; SMT Host state unknown\n", + mds_strings[mds_mitigation]); + } + + if (boot_cpu_has(X86_BUG_MSBDS_ONLY)) { + return sprintf(buf, "%s; SMT %s\n", mds_strings[mds_mitigation], + sched_smt_active() ? "mitigated" : "disabled"); + } + + return sprintf(buf, "%s; SMT %s\n", mds_strings[mds_mitigation], + sched_smt_active() ? "vulnerable" : "disabled"); +} + static char *stibp_state(void) { if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED) @@ -1238,6 +1254,10 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr if (boot_cpu_has(X86_FEATURE_L1TF_PTEINV)) return l1tf_show_state(buf); break; + + case X86_BUG_MDS: + return mds_show_state(buf); + default: break; } @@ -1269,4 +1289,9 @@ ssize_t cpu_show_l1tf(struct device *dev, struct device_attribute *attr, char *b { return cpu_show_common(dev, attr, buf, X86_BUG_L1TF); } + +ssize_t cpu_show_mds(struct device *dev, struct device_attribute *attr, char *buf) +{ + return cpu_show_common(dev, attr, buf, X86_BUG_MDS); +} #endif diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index eb9443d5bae1..2fd6ca1021c2 100644 --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -546,11 +546,18 @@ ssize_t __weak cpu_show_l1tf(struct device *dev, return sprintf(buf, "Not affected\n"); } +ssize_t __weak cpu_show_mds(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sprintf(buf, "Not affected\n"); +} + static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL); static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL); static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL); static DEVICE_ATTR(spec_store_bypass, 0444, cpu_show_spec_store_bypass, NULL); static DEVICE_ATTR(l1tf, 0444, cpu_show_l1tf, NULL); +static DEVICE_ATTR(mds, 0444, cpu_show_mds, NULL); static struct attribute *cpu_root_vulnerabilities_attrs[] = { &dev_attr_meltdown.attr, @@ -558,6 +565,7 @@ static struct attribute *cpu_root_vulnerabilities_attrs[] = { &dev_attr_spectre_v2.attr, &dev_attr_spec_store_bypass.attr, &dev_attr_l1tf.attr, + &dev_attr_mds.attr, NULL }; diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 5041357d0297..3c87ad888ed3 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -57,6 +57,8 @@ extern ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute *attr, char *buf); extern ssize_t cpu_show_l1tf(struct device *dev, struct device_attribute *attr, char *buf); +extern ssize_t cpu_show_mds(struct device *dev, + struct device_attribute *attr, char *buf); extern __printf(4, 5) struct device *cpu_device_create(struct device *parent, void *drvdata, -- cgit v1.2.3 From 22dd8365088b6403630b82423cf906491859b65e Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 20 Feb 2019 09:40:40 +0100 Subject: x86/speculation/mds: Add mitigation mode VMWERV In virtualized environments it can happen that the host has the microcode update which utilizes the VERW instruction to clear CPU buffers, but the hypervisor is not yet updated to expose the X86_FEATURE_MD_CLEAR CPUID bit to guests. Introduce an internal mitigation mode VMWERV which enables the invocation of the CPU buffer clearing even if X86_FEATURE_MD_CLEAR is not set. If the system has no updated microcode this results in a pointless execution of the VERW instruction wasting a few CPU cycles. If the microcode is updated, but not exposed to a guest then the CPU buffers will be cleared. That said: Virtual Machines Will Eventually Receive Vaccine Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Reviewed-by: Jon Masters Tested-by: Jon Masters --- Documentation/x86/mds.rst | 27 +++++++++++++++++++++++++++ arch/x86/include/asm/processor.h | 1 + arch/x86/kernel/cpu/bugs.c | 18 ++++++++++++------ 3 files changed, 40 insertions(+), 6 deletions(-) (limited to 'arch') diff --git a/Documentation/x86/mds.rst b/Documentation/x86/mds.rst index 87ce8ac9f36e..3d6f943f1afb 100644 --- a/Documentation/x86/mds.rst +++ b/Documentation/x86/mds.rst @@ -93,11 +93,38 @@ The kernel provides a function to invoke the buffer clearing: The mitigation is invoked on kernel/userspace, hypervisor/guest and C-state (idle) transitions. +As a special quirk to address virtualization scenarios where the host has +the microcode updated, but the hypervisor does not (yet) expose the +MD_CLEAR CPUID bit to guests, the kernel issues the VERW instruction in the +hope that it might actually clear the buffers. The state is reflected +accordingly. + According to current knowledge additional mitigations inside the kernel itself are not required because the necessary gadgets to expose the leaked data cannot be controlled in a way which allows exploitation from malicious user space or VM guests. +Kernel internal mitigation modes +-------------------------------- + + ======= ============================================================ + off Mitigation is disabled. Either the CPU is not affected or + mds=off is supplied on the kernel command line + + full Mitigation is eanbled. CPU is affected and MD_CLEAR is + advertised in CPUID. + + vmwerv Mitigation is enabled. CPU is affected and MD_CLEAR is not + advertised in CPUID. That is mainly for virtualization + scenarios where the host has the updated microcode but the + hypervisor does not expose MD_CLEAR in CPUID. It's a best + effort approach without guarantee. + ======= ============================================================ + +If the CPU is affected and mds=off is not supplied on the kernel command +line then the kernel selects the appropriate mitigation mode depending on +the availability of the MD_CLEAR CPUID bit. + Mitigation points ----------------- diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 1f0295783325..aca1ef8cc79f 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -995,6 +995,7 @@ extern enum l1tf_mitigations l1tf_mitigation; enum mds_mitigations { MDS_MITIGATION_OFF, MDS_MITIGATION_FULL, + MDS_MITIGATION_VMWERV, }; #endif /* _ASM_X86_PROCESSOR_H */ diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 7ab16a6ed064..95cda38c8785 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -224,7 +224,8 @@ static enum mds_mitigations mds_mitigation __ro_after_init = MDS_MITIGATION_FULL static const char * const mds_strings[] = { [MDS_MITIGATION_OFF] = "Vulnerable", - [MDS_MITIGATION_FULL] = "Mitigation: Clear CPU buffers" + [MDS_MITIGATION_FULL] = "Mitigation: Clear CPU buffers", + [MDS_MITIGATION_VMWERV] = "Vulnerable: Clear CPU buffers attempted, no microcode", }; static void __init mds_select_mitigation(void) @@ -235,10 +236,9 @@ static void __init mds_select_mitigation(void) } if (mds_mitigation == MDS_MITIGATION_FULL) { - if (boot_cpu_has(X86_FEATURE_MD_CLEAR)) - static_branch_enable(&mds_user_clear); - else - mds_mitigation = MDS_MITIGATION_OFF; + if (!boot_cpu_has(X86_FEATURE_MD_CLEAR)) + mds_mitigation = MDS_MITIGATION_VMWERV; + static_branch_enable(&mds_user_clear); } pr_info("%s\n", mds_strings[mds_mitigation]); } @@ -705,8 +705,14 @@ void arch_smt_update(void) break; } - if (mds_mitigation == MDS_MITIGATION_FULL) + switch (mds_mitigation) { + case MDS_MITIGATION_FULL: + case MDS_MITIGATION_VMWERV: update_mds_branch_idle(); + break; + case MDS_MITIGATION_OFF: + break; + } mutex_unlock(&spec_ctrl_mutex); } -- cgit v1.2.3 From 65fd4cb65b2dad97feb8330b6690445910b56d6a Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 19 Feb 2019 11:10:49 +0100 Subject: Documentation: Move L1TF to separate directory Move L!TF to a separate directory so the MDS stuff can be added at the side. Otherwise the all hardware vulnerabilites have their own top level entry. Should have done that right away. Signed-off-by: Thomas Gleixner Reviewed-by: Greg Kroah-Hartman Reviewed-by: Jon Masters --- Documentation/ABI/testing/sysfs-devices-system-cpu | 2 +- Documentation/admin-guide/hw-vuln/index.rst | 12 + Documentation/admin-guide/hw-vuln/l1tf.rst | 614 +++++++++++++++++++++ Documentation/admin-guide/index.rst | 6 +- Documentation/admin-guide/kernel-parameters.txt | 2 +- Documentation/admin-guide/l1tf.rst | 614 --------------------- arch/x86/kernel/cpu/bugs.c | 2 +- arch/x86/kvm/vmx/vmx.c | 4 +- 8 files changed, 633 insertions(+), 623 deletions(-) create mode 100644 Documentation/admin-guide/hw-vuln/index.rst create mode 100644 Documentation/admin-guide/hw-vuln/l1tf.rst delete mode 100644 Documentation/admin-guide/l1tf.rst (limited to 'arch') diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 2db5c3407fd6..744c6d764b0c 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -498,7 +498,7 @@ Description: Information about CPU vulnerabilities "Mitigation: $M" CPU is affected and mitigation $M is in effect Details about the l1tf file can be found in - Documentation/admin-guide/l1tf.rst + Documentation/admin-guide/hw-vuln/l1tf.rst What: /sys/devices/system/cpu/smt /sys/devices/system/cpu/smt/active diff --git a/Documentation/admin-guide/hw-vuln/index.rst b/Documentation/admin-guide/hw-vuln/index.rst new file mode 100644 index 000000000000..8ce2009f1981 --- /dev/null +++ b/Documentation/admin-guide/hw-vuln/index.rst @@ -0,0 +1,12 @@ +======================== +Hardware vulnerabilities +======================== + +This section describes CPU vulnerabilities and provides an overview of the +possible mitigations along with guidance for selecting mitigations if they +are configurable at compile, boot or run time. + +.. toctree:: + :maxdepth: 1 + + l1tf diff --git a/Documentation/admin-guide/hw-vuln/l1tf.rst b/Documentation/admin-guide/hw-vuln/l1tf.rst new file mode 100644 index 000000000000..9af977384168 --- /dev/null +++ b/Documentation/admin-guide/hw-vuln/l1tf.rst @@ -0,0 +1,614 @@ +L1TF - L1 Terminal Fault +======================== + +L1 Terminal Fault is a hardware vulnerability which allows unprivileged +speculative access to data which is available in the Level 1 Data Cache +when the page table entry controlling the virtual address, which is used +for the access, has the Present bit cleared or other reserved bits set. + +Affected processors +------------------- + +This vulnerability affects a wide range of Intel processors. The +vulnerability is not present on: + + - Processors from AMD, Centaur and other non Intel vendors + + - Older processor models, where the CPU family is < 6 + + - A range of Intel ATOM processors (Cedarview, Cloverview, Lincroft, + Penwell, Pineview, Silvermont, Airmont, Merrifield) + + - The Intel XEON PHI family + + - Intel processors which have the ARCH_CAP_RDCL_NO bit set in the + IA32_ARCH_CAPABILITIES MSR. If the bit is set the CPU is not affected + by the Meltdown vulnerability either. These CPUs should become + available by end of 2018. + +Whether a processor is affected or not can be read out from the L1TF +vulnerability file in sysfs. See :ref:`l1tf_sys_info`. + +Related CVEs +------------ + +The following CVE entries are related to the L1TF vulnerability: + + ============= ================= ============================== + CVE-2018-3615 L1 Terminal Fault SGX related aspects + CVE-2018-3620 L1 Terminal Fault OS, SMM related aspects + CVE-2018-3646 L1 Terminal Fault Virtualization related aspects + ============= ================= ============================== + +Problem +------- + +If an instruction accesses a virtual address for which the relevant page +table entry (PTE) has the Present bit cleared or other reserved bits set, +then speculative execution ignores the invalid PTE and loads the referenced +data if it is present in the Level 1 Data Cache, as if the page referenced +by the address bits in the PTE was still present and accessible. + +While this is a purely speculative mechanism and the instruction will raise +a page fault when it is retired eventually, the pure act of loading the +data and making it available to other speculative instructions opens up the +opportunity for side channel attacks to unprivileged malicious code, +similar to the Meltdown attack. + +While Meltdown breaks the user space to kernel space protection, L1TF +allows to attack any physical memory address in the system and the attack +works across all protection domains. It allows an attack of SGX and also +works from inside virtual machines because the speculation bypasses the +extended page table (EPT) protection mechanism. + + +Attack scenarios +---------------- + +1. Malicious user space +^^^^^^^^^^^^^^^^^^^^^^^ + + Operating Systems store arbitrary information in the address bits of a + PTE which is marked non present. This allows a malicious user space + application to attack the physical memory to which these PTEs resolve. + In some cases user-space can maliciously influence the information + encoded in the address bits of the PTE, thus making attacks more + deterministic and more practical. + + The Linux kernel contains a mitigation for this attack vector, PTE + inversion, which is permanently enabled and has no performance + impact. The kernel ensures that the address bits of PTEs, which are not + marked present, never point to cacheable physical memory space. + + A system with an up to date kernel is protected against attacks from + malicious user space applications. + +2. Malicious guest in a virtual machine +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + + The fact that L1TF breaks all domain protections allows malicious guest + OSes, which can control the PTEs directly, and malicious guest user + space applications, which run on an unprotected guest kernel lacking the + PTE inversion mitigation for L1TF, to attack physical host memory. + + A special aspect of L1TF in the context of virtualization is symmetric + multi threading (SMT). The Intel implementation of SMT is called + HyperThreading. The fact that Hyperthreads on the affected processors + share the L1 Data Cache (L1D) is important for this. As the flaw allows + only to attack data which is present in L1D, a malicious guest running + on one Hyperthread can attack the data which is brought into the L1D by + the context which runs on the sibling Hyperthread of the same physical + core. This context can be host OS, host user space or a different guest. + + If the processor does not support Extended Page Tables, the attack is + only possible, when the hypervisor does not sanitize the content of the + effective (shadow) page tables. + + While solutions exist to mitigate these attack vectors fully, these + mitigations are not enabled by default in the Linux kernel because they + can affect performance significantly. The kernel provides several + mechanisms which can be utilized to address the problem depending on the + deployment scenario. The mitigations, their protection scope and impact + are described in the next sections. + + The default mitigations and the rationale for choosing them are explained + at the end of this document. See :ref:`default_mitigations`. + +.. _l1tf_sys_info: + +L1TF system information +----------------------- + +The Linux kernel provides a sysfs interface to enumerate the current L1TF +status of the system: whether the system is vulnerable, and which +mitigations are active. The relevant sysfs file is: + +/sys/devices/system/cpu/vulnerabilities/l1tf + +The possible values in this file are: + + =========================== =============================== + 'Not affected' The processor is not vulnerable + 'Mitigation: PTE Inversion' The host protection is active + =========================== =============================== + +If KVM/VMX is enabled and the processor is vulnerable then the following +information is appended to the 'Mitigation: PTE Inversion' part: + + - SMT status: + + ===================== ================ + 'VMX: SMT vulnerable' SMT is enabled + 'VMX: SMT disabled' SMT is disabled + ===================== ================ + + - L1D Flush mode: + + ================================ ==================================== + 'L1D vulnerable' L1D flushing is disabled + + 'L1D conditional cache flushes' L1D flush is conditionally enabled + + 'L1D cache flushes' L1D flush is unconditionally enabled + ================================ ==================================== + +The resulting grade of protection is discussed in the following sections. + + +Host mitigation mechanism +------------------------- + +The kernel is unconditionally protected against L1TF attacks from malicious +user space running on the host. + + +Guest mitigation mechanisms +--------------------------- + +.. _l1d_flush: + +1. L1D flush on VMENTER +^^^^^^^^^^^^^^^^^^^^^^^ + + To make sure that a guest cannot attack data which is present in the L1D + the hypervisor flushes the L1D before entering the guest. + + Flushing the L1D evicts not only the data which should not be accessed + by a potentially malicious guest, it also flushes the guest + data. Flushing the L1D has a performance impact as the processor has to + bring the flushed guest data back into the L1D. Depending on the + frequency of VMEXIT/VMENTER and the type of computations in the guest + performance degradation in the range of 1% to 50% has been observed. For + scenarios where guest VMEXIT/VMENTER are rare the performance impact is + minimal. Virtio and mechanisms like posted interrupts are designed to + confine the VMEXITs to a bare minimum, but specific configurations and + application scenarios might still suffer from a high VMEXIT rate. + + The kernel provides two L1D flush modes: + - conditional ('cond') + - unconditional ('always') + + The conditional mode avoids L1D flushing after VMEXITs which execute + only audited code paths before the corresponding VMENTER. These code + paths have been verified that they cannot expose secrets or other + interesting data to an attacker, but they can leak information about the + address space layout of the hypervisor. + + Unconditional mode flushes L1D on all VMENTER invocations and provides + maximum protection. It has a higher overhead than the conditional + mode. The overhead cannot be quantified correctly as it depends on the + workload scenario and the resulting number of VMEXITs. + + The general recommendation is to enable L1D flush on VMENTER. The kernel + defaults to conditional mode on affected processors. + + **Note**, that L1D flush does not prevent the SMT problem because the + sibling thread will also bring back its data into the L1D which makes it + attackable again. + + L1D flush can be controlled by the administrator via the kernel command + line and sysfs control files. See :ref:`mitigation_control_command_line` + and :ref:`mitigation_control_kvm`. + +.. _guest_confinement: + +2. Guest VCPU confinement to dedicated physical cores +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + + To address the SMT problem, it is possible to make a guest or a group of + guests affine to one or more physical cores. The proper mechanism for + that is to utilize exclusive cpusets to ensure that no other guest or + host tasks can run on these cores. + + If only a single guest or related guests run on sibling SMT threads on + the same physical core then they can only attack their own memory and + restricted parts of the host memory. + + Host memory is attackable, when one of the sibling SMT threads runs in + host OS (hypervisor) context and the other in guest context. The amount + of valuable information from the host OS context depends on the context + which the host OS executes, i.e. interrupts, soft interrupts and kernel + threads. The amount of valuable data from these contexts cannot be + declared as non-interesting for an attacker without deep inspection of + the code. + + **Note**, that assigning guests to a fixed set of physical cores affects + the ability of the scheduler to do load balancing and might have + negative effects on CPU utilization depending on the hosting + scenario. Disabling SMT might be a viable alternative for particular + scenarios. + + For further information about confining guests to a single or to a group + of cores consult the cpusets documentation: + + https://www.kernel.org/doc/Documentation/cgroup-v1/cpusets.txt + +.. _interrupt_isolation: + +3. Interrupt affinity +^^^^^^^^^^^^^^^^^^^^^ + + Interrupts can be made affine to logical CPUs. This is not universally + true because there are types of interrupts which are truly per CPU + interrupts, e.g. the local timer interrupt. Aside of that multi queue + devices affine their interrupts to single CPUs or groups of CPUs per + queue without allowing the administrator to control the affinities. + + Moving the interrupts, which can be affinity controlled, away from CPUs + which run untrusted guests, reduces the attack vector space. + + Whether the interrupts with are affine to CPUs, which run untrusted + guests, provide interesting data for an attacker depends on the system + configuration and the scenarios which run on the system. While for some + of the interrupts it can be assumed that they won't expose interesting + information beyond exposing hints about the host OS memory layout, there + is no way to make general assumptions. + + Interrupt affinity can be controlled by the administrator via the + /proc/irq/$NR/smp_affinity[_list] files. Limited documentation is + available at: + + https://www.kernel.org/doc/Documentation/IRQ-affinity.txt + +.. _smt_control: + +4. SMT control +^^^^^^^^^^^^^^ + + To prevent the SMT issues of L1TF it might be necessary to disable SMT + completely. Disabling SMT can have a significant performance impact, but + the impact depends on the hosting scenario and the type of workloads. + The impact of disabling SMT needs also to be weighted against the impact + of other mitigation solutions like confining guests to dedicated cores. + + The kernel provides a sysfs interface to retrieve the status of SMT and + to control it. It also provides a kernel command line interface to + control SMT. + + The kernel command line interface consists of the following options: + + =========== ========================================================== + nosmt Affects the bring up of the secondary CPUs during boot. The + kernel tries to bring all present CPUs online during the + boot process. "nosmt" makes sure that from each physical + core only one - the so called primary (hyper) thread is + activated. Due to a design flaw of Intel processors related + to Machine Check Exceptions the non primary siblings have + to be brought up at least partially and are then shut down + again. "nosmt" can be undone via the sysfs interface. + + nosmt=force Has the same effect as "nosmt" but it does not allow to + undo the SMT disable via the sysfs interface. + =========== ========================================================== + + The sysfs interface provides two files: + + - /sys/devices/system/cpu/smt/control + - /sys/devices/system/cpu/smt/active + + /sys/devices/system/cpu/smt/control: + + This file allows to read out the SMT control state and provides the + ability to disable or (re)enable SMT. The possible states are: + + ============== =================================================== + on SMT is supported by the CPU and enabled. All + logical CPUs can be onlined and offlined without + restrictions. + + off SMT is supported by the CPU and disabled. Only + the so called primary SMT threads can be onlined + and offlined without restrictions. An attempt to + online a non-primary sibling is rejected + + forceoff Same as 'off' but the state cannot be controlled. + Attempts to write to the control file are rejected. + + notsupported The processor does not support SMT. It's therefore + not affected by the SMT implications of L1TF. + Attempts to write to the control file are rejected. + ============== =================================================== + + The possible states which can be written into this file to control SMT + state are: + + - on + - off + - forceoff + + /sys/devices/system/cpu/smt/active: + + This file reports whether SMT is enabled and active, i.e. if on any + physical core two or more sibling threads are online. + + SMT control is also possible at boot time via the l1tf kernel command + line parameter in combination with L1D flush control. See + :ref:`mitigation_control_command_line`. + +5. Disabling EPT +^^^^^^^^^^^^^^^^ + + Disabling EPT for virtual machines provides full mitigation for L1TF even + with SMT enabled, because the effective page tables for guests are + managed and sanitized by the hypervisor. Though disabling EPT has a + significant performance impact especially when the Meltdown mitigation + KPTI is enabled. + + EPT can be disabled in the hypervisor via the 'kvm-intel.ept' parameter. + +There is ongoing research and development for new mitigation mechanisms to +address the performance impact of disabling SMT or EPT. + +.. _mitigation_control_command_line: + +Mitigation control on the kernel command line +--------------------------------------------- + +The kernel command line allows to control the L1TF mitigations at boot +time with the option "l1tf=". The valid arguments for this option are: + + ============ ============================================================= + full Provides all available mitigations for the L1TF + vulnerability. Disables SMT and enables all mitigations in + the hypervisors, i.e. unconditional L1D flushing + + SMT control and L1D flush control via the sysfs interface + is still possible after boot. Hypervisors will issue a + warning when the first VM is started in a potentially + insecure configuration, i.e. SMT enabled or L1D flush + disabled. + + full,force Same as 'full', but disables SMT and L1D flush runtime + control. Implies the 'nosmt=force' command line option. + (i.e. sysfs control of SMT is disabled.) + + flush Leaves SMT enabled and enables the default hypervisor + mitigation, i.e. conditional L1D flushing + + SMT control and L1D flush control via the sysfs interface + is still possible after boot. Hypervisors will issue a + warning when the first VM is started in a potentially + insecure configuration, i.e. SMT enabled or L1D flush + disabled. + + flush,nosmt Disables SMT and enables the default hypervisor mitigation, + i.e. conditional L1D flushing. + + SMT control and L1D flush control via the sysfs interface + is still possible after boot. Hypervisors will issue a + warning when the first VM is started in a potentially + insecure configuration, i.e. SMT enabled or L1D flush + disabled. + + flush,nowarn Same as 'flush', but hypervisors will not warn when a VM is + started in a potentially insecure configuration. + + off Disables hypervisor mitigations and doesn't emit any + warnings. + It also drops the swap size and available RAM limit restrictions + on both hypervisor and bare metal. + + ============ ============================================================= + +The default is 'flush'. For details about L1D flushing see :ref:`l1d_flush`. + + +.. _mitigation_control_kvm: + +Mitigation control for KVM - module parameter +------------------------------------------------------------- + +The KVM hypervisor mitigation mechanism, flushing the L1D cache when +entering a guest, can be controlled with a module parameter. + +The option/parameter is "kvm-intel.vmentry_l1d_flush=". It takes the +following arguments: + + ============ ============================================================== + always L1D cache flush on every VMENTER. + + cond Flush L1D on VMENTER only when the code between VMEXIT and + VMENTER can leak host memory which is considered + interesting for an attacker. This still can leak host memory + which allows e.g. to determine the hosts address space layout. + + never Disables the mitigation + ============ ============================================================== + +The parameter can be provided on the kernel command line, as a module +parameter when loading the modules and at runtime modified via the sysfs +file: + +/sys/module/kvm_intel/parameters/vmentry_l1d_flush + +The default is 'cond'. If 'l1tf=full,force' is given on the kernel command +line, then 'always' is enforced and the kvm-intel.vmentry_l1d_flush +module parameter is ignored and writes to the sysfs file are rejected. + + +Mitigation selection guide +-------------------------- + +1. No virtualization in use +^^^^^^^^^^^^^^^^^^^^^^^^^^^ + + The system is protected by the kernel unconditionally and no further + action is required. + +2. Virtualization with trusted guests +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + + If the guest comes from a trusted source and the guest OS kernel is + guaranteed to have the L1TF mitigations in place the system is fully + protected against L1TF and no further action is required. + + To avoid the overhead of the default L1D flushing on VMENTER the + administrator can disable the flushing via the kernel command line and + sysfs control files. See :ref:`mitigation_control_command_line` and + :ref:`mitigation_control_kvm`. + + +3. Virtualization with untrusted guests +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +3.1. SMT not supported or disabled +"""""""""""""""""""""""""""""""""" + + If SMT is not supported by the processor or disabled in the BIOS or by + the kernel, it's only required to enforce L1D flushing on VMENTER. + + Conditional L1D flushing is the default behaviour and can be tuned. See + :ref:`mitigation_control_command_line` and :ref:`mitigation_control_kvm`. + +3.2. EPT not supported or disabled +"""""""""""""""""""""""""""""""""" + + If EPT is not supported by the processor or disabled in the hypervisor, + the system is fully protected. SMT can stay enabled and L1D flushing on + VMENTER is not required. + + EPT can be disabled in the hypervisor via the 'kvm-intel.ept' parameter. + +3.3. SMT and EPT supported and active +""""""""""""""""""""""""""""""""""""" + + If SMT and EPT are supported and active then various degrees of + mitigations can be employed: + + - L1D flushing on VMENTER: + + L1D flushing on VMENTER is the minimal protection requirement, but it + is only potent in combination with other mitigation methods. + + Conditional L1D flushing is the default behaviour and can be tuned. See + :ref:`mitigation_control_command_line` and :ref:`mitigation_control_kvm`. + + - Guest confinement: + + Confinement of guests to a single or a group of physical cores which + are not running any other processes, can reduce the attack surface + significantly, but interrupts, soft interrupts and kernel threads can + still expose valuable data to a potential attacker. See + :ref:`guest_confinement`. + + - Interrupt isolation: + + Isolating the guest CPUs from interrupts can reduce the attack surface + further, but still allows a malicious guest to explore a limited amount + of host physical memory. This can at least be used to gain knowledge + about the host address space layout. The interrupts which have a fixed + affinity to the CPUs which run the untrusted guests can depending on + the scenario still trigger soft interrupts and schedule kernel threads + which might expose valuable information. See + :ref:`interrupt_isolation`. + +The above three mitigation methods combined can provide protection to a +certain degree, but the risk of the remaining attack surface has to be +carefully analyzed. For full protection the following methods are +available: + + - Disabling SMT: + + Disabling SMT and enforcing the L1D flushing provides the maximum + amount of protection. This mitigation is not depending on any of the + above mitigation methods. + + SMT control and L1D flushing can be tuned by the command line + parameters 'nosmt', 'l1tf', 'kvm-intel.vmentry_l1d_flush' and at run + time with the matching sysfs control files. See :ref:`smt_control`, + :ref:`mitigation_control_command_line` and + :ref:`mitigation_control_kvm`. + + - Disabling EPT: + + Disabling EPT provides the maximum amount of protection as well. It is + not depending on any of the above mitigation methods. SMT can stay + enabled and L1D flushing is not required, but the performance impact is + significant. + + EPT can be disabled in the hypervisor via the 'kvm-intel.ept' + parameter. + +3.4. Nested virtual machines +"""""""""""""""""""""""""""" + +When nested virtualization is in use, three operating systems are involved: +the bare metal hypervisor, the nested hypervisor and the nested virtual +machine. VMENTER operations from the nested hypervisor into the nested +guest will always be processed by the bare metal hypervisor. If KVM is the +bare metal hypervisor it will: + + - Flush the L1D cache on every switch from the nested hypervisor to the + nested virtual machine, so that the nested hypervisor's secrets are not + exposed to the nested virtual machine; + + - Flush the L1D cache on every switch from the nested virtual machine to + the nested hypervisor; this is a complex operation, and flushing the L1D + cache avoids that the bare metal hypervisor's secrets are exposed to the + nested virtual machine; + + - Instruct the nested hypervisor to not perform any L1D cache flush. This + is an optimization to avoid double L1D flushing. + + +.. _default_mitigations: + +Default mitigations +------------------- + + The kernel default mitigations for vulnerable processors are: + + - PTE inversion to protect against malicious user space. This is done + unconditionally and cannot be controlled. The swap storage is limited + to ~16TB. + + - L1D conditional flushing on VMENTER when EPT is enabled for + a guest. + + The kernel does not by default enforce the disabling of SMT, which leaves + SMT systems vulnerable when running untrusted guests with EPT enabled. + + The rationale for this choice is: + + - Force disabling SMT can break existing setups, especially with + unattended updates. + + - If regular users run untrusted guests on their machine, then L1TF is + just an add on to other malware which might be embedded in an untrusted + guest, e.g. spam-bots or attacks on the local network. + + There is no technical way to prevent a user from running untrusted code + on their machines blindly. + + - It's technically extremely unlikely and from today's knowledge even + impossible that L1TF can be exploited via the most popular attack + mechanisms like JavaScript because these mechanisms have no way to + control PTEs. If this would be possible and not other mitigation would + be possible, then the default might be different. + + - The administrators of cloud and hosting setups have to carefully + analyze the risk for their scenarios and make the appropriate + mitigation choices, which might even vary across their deployed + machines and also result in other changes of their overall setup. + There is no way for the kernel to provide a sensible default for this + kind of scenarios. diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst index 0a491676685e..42247516962a 100644 --- a/Documentation/admin-guide/index.rst +++ b/Documentation/admin-guide/index.rst @@ -17,14 +17,12 @@ etc. kernel-parameters devices -This section describes CPU vulnerabilities and provides an overview of the -possible mitigations along with guidance for selecting mitigations if they -are configurable at compile, boot or run time. +This section describes CPU vulnerabilities and their mitigations. .. toctree:: :maxdepth: 1 - l1tf + hw-vuln/index Here is a set of documents aimed at users who are trying to track down problems and bugs in particular. diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index dddb024eb523..9afcb240a673 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2114,7 +2114,7 @@ Default is 'flush'. - For details see: Documentation/admin-guide/l1tf.rst + For details see: Documentation/admin-guide/hw-vuln/l1tf.rst l2cr= [PPC] diff --git a/Documentation/admin-guide/l1tf.rst b/Documentation/admin-guide/l1tf.rst deleted file mode 100644 index 9af977384168..000000000000 --- a/Documentation/admin-guide/l1tf.rst +++ /dev/null @@ -1,614 +0,0 @@ -L1TF - L1 Terminal Fault -======================== - -L1 Terminal Fault is a hardware vulnerability which allows unprivileged -speculative access to data which is available in the Level 1 Data Cache -when the page table entry controlling the virtual address, which is used -for the access, has the Present bit cleared or other reserved bits set. - -Affected processors -------------------- - -This vulnerability affects a wide range of Intel processors. The -vulnerability is not present on: - - - Processors from AMD, Centaur and other non Intel vendors - - - Older processor models, where the CPU family is < 6 - - - A range of Intel ATOM processors (Cedarview, Cloverview, Lincroft, - Penwell, Pineview, Silvermont, Airmont, Merrifield) - - - The Intel XEON PHI family - - - Intel processors which have the ARCH_CAP_RDCL_NO bit set in the - IA32_ARCH_CAPABILITIES MSR. If the bit is set the CPU is not affected - by the Meltdown vulnerability either. These CPUs should become - available by end of 2018. - -Whether a processor is affected or not can be read out from the L1TF -vulnerability file in sysfs. See :ref:`l1tf_sys_info`. - -Related CVEs ------------- - -The following CVE entries are related to the L1TF vulnerability: - - ============= ================= ============================== - CVE-2018-3615 L1 Terminal Fault SGX related aspects - CVE-2018-3620 L1 Terminal Fault OS, SMM related aspects - CVE-2018-3646 L1 Terminal Fault Virtualization related aspects - ============= ================= ============================== - -Problem -------- - -If an instruction accesses a virtual address for which the relevant page -table entry (PTE) has the Present bit cleared or other reserved bits set, -then speculative execution ignores the invalid PTE and loads the referenced -data if it is present in the Level 1 Data Cache, as if the page referenced -by the address bits in the PTE was still present and accessible. - -While this is a purely speculative mechanism and the instruction will raise -a page fault when it is retired eventually, the pure act of loading the -data and making it available to other speculative instructions opens up the -opportunity for side channel attacks to unprivileged malicious code, -similar to the Meltdown attack. - -While Meltdown breaks the user space to kernel space protection, L1TF -allows to attack any physical memory address in the system and the attack -works across all protection domains. It allows an attack of SGX and also -works from inside virtual machines because the speculation bypasses the -extended page table (EPT) protection mechanism. - - -Attack scenarios ----------------- - -1. Malicious user space -^^^^^^^^^^^^^^^^^^^^^^^ - - Operating Systems store arbitrary information in the address bits of a - PTE which is marked non present. This allows a malicious user space - application to attack the physical memory to which these PTEs resolve. - In some cases user-space can maliciously influence the information - encoded in the address bits of the PTE, thus making attacks more - deterministic and more practical. - - The Linux kernel contains a mitigation for this attack vector, PTE - inversion, which is permanently enabled and has no performance - impact. The kernel ensures that the address bits of PTEs, which are not - marked present, never point to cacheable physical memory space. - - A system with an up to date kernel is protected against attacks from - malicious user space applications. - -2. Malicious guest in a virtual machine -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - - The fact that L1TF breaks all domain protections allows malicious guest - OSes, which can control the PTEs directly, and malicious guest user - space applications, which run on an unprotected guest kernel lacking the - PTE inversion mitigation for L1TF, to attack physical host memory. - - A special aspect of L1TF in the context of virtualization is symmetric - multi threading (SMT). The Intel implementation of SMT is called - HyperThreading. The fact that Hyperthreads on the affected processors - share the L1 Data Cache (L1D) is important for this. As the flaw allows - only to attack data which is present in L1D, a malicious guest running - on one Hyperthread can attack the data which is brought into the L1D by - the context which runs on the sibling Hyperthread of the same physical - core. This context can be host OS, host user space or a different guest. - - If the processor does not support Extended Page Tables, the attack is - only possible, when the hypervisor does not sanitize the content of the - effective (shadow) page tables. - - While solutions exist to mitigate these attack vectors fully, these - mitigations are not enabled by default in the Linux kernel because they - can affect performance significantly. The kernel provides several - mechanisms which can be utilized to address the problem depending on the - deployment scenario. The mitigations, their protection scope and impact - are described in the next sections. - - The default mitigations and the rationale for choosing them are explained - at the end of this document. See :ref:`default_mitigations`. - -.. _l1tf_sys_info: - -L1TF system information ------------------------ - -The Linux kernel provides a sysfs interface to enumerate the current L1TF -status of the system: whether the system is vulnerable, and which -mitigations are active. The relevant sysfs file is: - -/sys/devices/system/cpu/vulnerabilities/l1tf - -The possible values in this file are: - - =========================== =============================== - 'Not affected' The processor is not vulnerable - 'Mitigation: PTE Inversion' The host protection is active - =========================== =============================== - -If KVM/VMX is enabled and the processor is vulnerable then the following -information is appended to the 'Mitigation: PTE Inversion' part: - - - SMT status: - - ===================== ================ - 'VMX: SMT vulnerable' SMT is enabled - 'VMX: SMT disabled' SMT is disabled - ===================== ================ - - - L1D Flush mode: - - ================================ ==================================== - 'L1D vulnerable' L1D flushing is disabled - - 'L1D conditional cache flushes' L1D flush is conditionally enabled - - 'L1D cache flushes' L1D flush is unconditionally enabled - ================================ ==================================== - -The resulting grade of protection is discussed in the following sections. - - -Host mitigation mechanism -------------------------- - -The kernel is unconditionally protected against L1TF attacks from malicious -user space running on the host. - - -Guest mitigation mechanisms ---------------------------- - -.. _l1d_flush: - -1. L1D flush on VMENTER -^^^^^^^^^^^^^^^^^^^^^^^ - - To make sure that a guest cannot attack data which is present in the L1D - the hypervisor flushes the L1D before entering the guest. - - Flushing the L1D evicts not only the data which should not be accessed - by a potentially malicious guest, it also flushes the guest - data. Flushing the L1D has a performance impact as the processor has to - bring the flushed guest data back into the L1D. Depending on the - frequency of VMEXIT/VMENTER and the type of computations in the guest - performance degradation in the range of 1% to 50% has been observed. For - scenarios where guest VMEXIT/VMENTER are rare the performance impact is - minimal. Virtio and mechanisms like posted interrupts are designed to - confine the VMEXITs to a bare minimum, but specific configurations and - application scenarios might still suffer from a high VMEXIT rate. - - The kernel provides two L1D flush modes: - - conditional ('cond') - - unconditional ('always') - - The conditional mode avoids L1D flushing after VMEXITs which execute - only audited code paths before the corresponding VMENTER. These code - paths have been verified that they cannot expose secrets or other - interesting data to an attacker, but they can leak information about the - address space layout of the hypervisor. - - Unconditional mode flushes L1D on all VMENTER invocations and provides - maximum protection. It has a higher overhead than the conditional - mode. The overhead cannot be quantified correctly as it depends on the - workload scenario and the resulting number of VMEXITs. - - The general recommendation is to enable L1D flush on VMENTER. The kernel - defaults to conditional mode on affected processors. - - **Note**, that L1D flush does not prevent the SMT problem because the - sibling thread will also bring back its data into the L1D which makes it - attackable again. - - L1D flush can be controlled by the administrator via the kernel command - line and sysfs control files. See :ref:`mitigation_control_command_line` - and :ref:`mitigation_control_kvm`. - -.. _guest_confinement: - -2. Guest VCPU confinement to dedicated physical cores -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - - To address the SMT problem, it is possible to make a guest or a group of - guests affine to one or more physical cores. The proper mechanism for - that is to utilize exclusive cpusets to ensure that no other guest or - host tasks can run on these cores. - - If only a single guest or related guests run on sibling SMT threads on - the same physical core then they can only attack their own memory and - restricted parts of the host memory. - - Host memory is attackable, when one of the sibling SMT threads runs in - host OS (hypervisor) context and the other in guest context. The amount - of valuable information from the host OS context depends on the context - which the host OS executes, i.e. interrupts, soft interrupts and kernel - threads. The amount of valuable data from these contexts cannot be - declared as non-interesting for an attacker without deep inspection of - the code. - - **Note**, that assigning guests to a fixed set of physical cores affects - the ability of the scheduler to do load balancing and might have - negative effects on CPU utilization depending on the hosting - scenario. Disabling SMT might be a viable alternative for particular - scenarios. - - For further information about confining guests to a single or to a group - of cores consult the cpusets documentation: - - https://www.kernel.org/doc/Documentation/cgroup-v1/cpusets.txt - -.. _interrupt_isolation: - -3. Interrupt affinity -^^^^^^^^^^^^^^^^^^^^^ - - Interrupts can be made affine to logical CPUs. This is not universally - true because there are types of interrupts which are truly per CPU - interrupts, e.g. the local timer interrupt. Aside of that multi queue - devices affine their interrupts to single CPUs or groups of CPUs per - queue without allowing the administrator to control the affinities. - - Moving the interrupts, which can be affinity controlled, away from CPUs - which run untrusted guests, reduces the attack vector space. - - Whether the interrupts with are affine to CPUs, which run untrusted - guests, provide interesting data for an attacker depends on the system - configuration and the scenarios which run on the system. While for some - of the interrupts it can be assumed that they won't expose interesting - information beyond exposing hints about the host OS memory layout, there - is no way to make general assumptions. - - Interrupt affinity can be controlled by the administrator via the - /proc/irq/$NR/smp_affinity[_list] files. Limited documentation is - available at: - - https://www.kernel.org/doc/Documentation/IRQ-affinity.txt - -.. _smt_control: - -4. SMT control -^^^^^^^^^^^^^^ - - To prevent the SMT issues of L1TF it might be necessary to disable SMT - completely. Disabling SMT can have a significant performance impact, but - the impact depends on the hosting scenario and the type of workloads. - The impact of disabling SMT needs also to be weighted against the impact - of other mitigation solutions like confining guests to dedicated cores. - - The kernel provides a sysfs interface to retrieve the status of SMT and - to control it. It also provides a kernel command line interface to - control SMT. - - The kernel command line interface consists of the following options: - - =========== ========================================================== - nosmt Affects the bring up of the secondary CPUs during boot. The - kernel tries to bring all present CPUs online during the - boot process. "nosmt" makes sure that from each physical - core only one - the so called primary (hyper) thread is - activated. Due to a design flaw of Intel processors related - to Machine Check Exceptions the non primary siblings have - to be brought up at least partially and are then shut down - again. "nosmt" can be undone via the sysfs interface. - - nosmt=force Has the same effect as "nosmt" but it does not allow to - undo the SMT disable via the sysfs interface. - =========== ========================================================== - - The sysfs interface provides two files: - - - /sys/devices/system/cpu/smt/control - - /sys/devices/system/cpu/smt/active - - /sys/devices/system/cpu/smt/control: - - This file allows to read out the SMT control state and provides the - ability to disable or (re)enable SMT. The possible states are: - - ============== =================================================== - on SMT is supported by the CPU and enabled. All - logical CPUs can be onlined and offlined without - restrictions. - - off SMT is supported by the CPU and disabled. Only - the so called primary SMT threads can be onlined - and offlined without restrictions. An attempt to - online a non-primary sibling is rejected - - forceoff Same as 'off' but the state cannot be controlled. - Attempts to write to the control file are rejected. - - notsupported The processor does not support SMT. It's therefore - not affected by the SMT implications of L1TF. - Attempts to write to the control file are rejected. - ============== =================================================== - - The possible states which can be written into this file to control SMT - state are: - - - on - - off - - forceoff - - /sys/devices/system/cpu/smt/active: - - This file reports whether SMT is enabled and active, i.e. if on any - physical core two or more sibling threads are online. - - SMT control is also possible at boot time via the l1tf kernel command - line parameter in combination with L1D flush control. See - :ref:`mitigation_control_command_line`. - -5. Disabling EPT -^^^^^^^^^^^^^^^^ - - Disabling EPT for virtual machines provides full mitigation for L1TF even - with SMT enabled, because the effective page tables for guests are - managed and sanitized by the hypervisor. Though disabling EPT has a - significant performance impact especially when the Meltdown mitigation - KPTI is enabled. - - EPT can be disabled in the hypervisor via the 'kvm-intel.ept' parameter. - -There is ongoing research and development for new mitigation mechanisms to -address the performance impact of disabling SMT or EPT. - -.. _mitigation_control_command_line: - -Mitigation control on the kernel command line ---------------------------------------------- - -The kernel command line allows to control the L1TF mitigations at boot -time with the option "l1tf=". The valid arguments for this option are: - - ============ ============================================================= - full Provides all available mitigations for the L1TF - vulnerability. Disables SMT and enables all mitigations in - the hypervisors, i.e. unconditional L1D flushing - - SMT control and L1D flush control via the sysfs interface - is still possible after boot. Hypervisors will issue a - warning when the first VM is started in a potentially - insecure configuration, i.e. SMT enabled or L1D flush - disabled. - - full,force Same as 'full', but disables SMT and L1D flush runtime - control. Implies the 'nosmt=force' command line option. - (i.e. sysfs control of SMT is disabled.) - - flush Leaves SMT enabled and enables the default hypervisor - mitigation, i.e. conditional L1D flushing - - SMT control and L1D flush control via the sysfs interface - is still possible after boot. Hypervisors will issue a - warning when the first VM is started in a potentially - insecure configuration, i.e. SMT enabled or L1D flush - disabled. - - flush,nosmt Disables SMT and enables the default hypervisor mitigation, - i.e. conditional L1D flushing. - - SMT control and L1D flush control via the sysfs interface - is still possible after boot. Hypervisors will issue a - warning when the first VM is started in a potentially - insecure configuration, i.e. SMT enabled or L1D flush - disabled. - - flush,nowarn Same as 'flush', but hypervisors will not warn when a VM is - started in a potentially insecure configuration. - - off Disables hypervisor mitigations and doesn't emit any - warnings. - It also drops the swap size and available RAM limit restrictions - on both hypervisor and bare metal. - - ============ ============================================================= - -The default is 'flush'. For details about L1D flushing see :ref:`l1d_flush`. - - -.. _mitigation_control_kvm: - -Mitigation control for KVM - module parameter -------------------------------------------------------------- - -The KVM hypervisor mitigation mechanism, flushing the L1D cache when -entering a guest, can be controlled with a module parameter. - -The option/parameter is "kvm-intel.vmentry_l1d_flush=". It takes the -following arguments: - - ============ ============================================================== - always L1D cache flush on every VMENTER. - - cond Flush L1D on VMENTER only when the code between VMEXIT and - VMENTER can leak host memory which is considered - interesting for an attacker. This still can leak host memory - which allows e.g. to determine the hosts address space layout. - - never Disables the mitigation - ============ ============================================================== - -The parameter can be provided on the kernel command line, as a module -parameter when loading the modules and at runtime modified via the sysfs -file: - -/sys/module/kvm_intel/parameters/vmentry_l1d_flush - -The default is 'cond'. If 'l1tf=full,force' is given on the kernel command -line, then 'always' is enforced and the kvm-intel.vmentry_l1d_flush -module parameter is ignored and writes to the sysfs file are rejected. - - -Mitigation selection guide --------------------------- - -1. No virtualization in use -^^^^^^^^^^^^^^^^^^^^^^^^^^^ - - The system is protected by the kernel unconditionally and no further - action is required. - -2. Virtualization with trusted guests -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - - If the guest comes from a trusted source and the guest OS kernel is - guaranteed to have the L1TF mitigations in place the system is fully - protected against L1TF and no further action is required. - - To avoid the overhead of the default L1D flushing on VMENTER the - administrator can disable the flushing via the kernel command line and - sysfs control files. See :ref:`mitigation_control_command_line` and - :ref:`mitigation_control_kvm`. - - -3. Virtualization with untrusted guests -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -3.1. SMT not supported or disabled -"""""""""""""""""""""""""""""""""" - - If SMT is not supported by the processor or disabled in the BIOS or by - the kernel, it's only required to enforce L1D flushing on VMENTER. - - Conditional L1D flushing is the default behaviour and can be tuned. See - :ref:`mitigation_control_command_line` and :ref:`mitigation_control_kvm`. - -3.2. EPT not supported or disabled -"""""""""""""""""""""""""""""""""" - - If EPT is not supported by the processor or disabled in the hypervisor, - the system is fully protected. SMT can stay enabled and L1D flushing on - VMENTER is not required. - - EPT can be disabled in the hypervisor via the 'kvm-intel.ept' parameter. - -3.3. SMT and EPT supported and active -""""""""""""""""""""""""""""""""""""" - - If SMT and EPT are supported and active then various degrees of - mitigations can be employed: - - - L1D flushing on VMENTER: - - L1D flushing on VMENTER is the minimal protection requirement, but it - is only potent in combination with other mitigation methods. - - Conditional L1D flushing is the default behaviour and can be tuned. See - :ref:`mitigation_control_command_line` and :ref:`mitigation_control_kvm`. - - - Guest confinement: - - Confinement of guests to a single or a group of physical cores which - are not running any other processes, can reduce the attack surface - significantly, but interrupts, soft interrupts and kernel threads can - still expose valuable data to a potential attacker. See - :ref:`guest_confinement`. - - - Interrupt isolation: - - Isolating the guest CPUs from interrupts can reduce the attack surface - further, but still allows a malicious guest to explore a limited amount - of host physical memory. This can at least be used to gain knowledge - about the host address space layout. The interrupts which have a fixed - affinity to the CPUs which run the untrusted guests can depending on - the scenario still trigger soft interrupts and schedule kernel threads - which might expose valuable information. See - :ref:`interrupt_isolation`. - -The above three mitigation methods combined can provide protection to a -certain degree, but the risk of the remaining attack surface has to be -carefully analyzed. For full protection the following methods are -available: - - - Disabling SMT: - - Disabling SMT and enforcing the L1D flushing provides the maximum - amount of protection. This mitigation is not depending on any of the - above mitigation methods. - - SMT control and L1D flushing can be tuned by the command line - parameters 'nosmt', 'l1tf', 'kvm-intel.vmentry_l1d_flush' and at run - time with the matching sysfs control files. See :ref:`smt_control`, - :ref:`mitigation_control_command_line` and - :ref:`mitigation_control_kvm`. - - - Disabling EPT: - - Disabling EPT provides the maximum amount of protection as well. It is - not depending on any of the above mitigation methods. SMT can stay - enabled and L1D flushing is not required, but the performance impact is - significant. - - EPT can be disabled in the hypervisor via the 'kvm-intel.ept' - parameter. - -3.4. Nested virtual machines -"""""""""""""""""""""""""""" - -When nested virtualization is in use, three operating systems are involved: -the bare metal hypervisor, the nested hypervisor and the nested virtual -machine. VMENTER operations from the nested hypervisor into the nested -guest will always be processed by the bare metal hypervisor. If KVM is the -bare metal hypervisor it will: - - - Flush the L1D cache on every switch from the nested hypervisor to the - nested virtual machine, so that the nested hypervisor's secrets are not - exposed to the nested virtual machine; - - - Flush the L1D cache on every switch from the nested virtual machine to - the nested hypervisor; this is a complex operation, and flushing the L1D - cache avoids that the bare metal hypervisor's secrets are exposed to the - nested virtual machine; - - - Instruct the nested hypervisor to not perform any L1D cache flush. This - is an optimization to avoid double L1D flushing. - - -.. _default_mitigations: - -Default mitigations -------------------- - - The kernel default mitigations for vulnerable processors are: - - - PTE inversion to protect against malicious user space. This is done - unconditionally and cannot be controlled. The swap storage is limited - to ~16TB. - - - L1D conditional flushing on VMENTER when EPT is enabled for - a guest. - - The kernel does not by default enforce the disabling of SMT, which leaves - SMT systems vulnerable when running untrusted guests with EPT enabled. - - The rationale for this choice is: - - - Force disabling SMT can break existing setups, especially with - unattended updates. - - - If regular users run untrusted guests on their machine, then L1TF is - just an add on to other malware which might be embedded in an untrusted - guest, e.g. spam-bots or attacks on the local network. - - There is no technical way to prevent a user from running untrusted code - on their machines blindly. - - - It's technically extremely unlikely and from today's knowledge even - impossible that L1TF can be exploited via the most popular attack - mechanisms like JavaScript because these mechanisms have no way to - control PTEs. If this would be possible and not other mitigation would - be possible, then the default might be different. - - - The administrators of cloud and hosting setups have to carefully - analyze the risk for their scenarios and make the appropriate - mitigation choices, which might even vary across their deployed - machines and also result in other changes of their overall setup. - There is no way for the kernel to provide a sensible default for this - kind of scenarios. diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 95cda38c8785..373ae1dcd301 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1107,7 +1107,7 @@ static void __init l1tf_select_mitigation(void) pr_info("You may make it effective by booting the kernel with mem=%llu parameter.\n", half_pa); pr_info("However, doing so will make a part of your RAM unusable.\n"); - pr_info("Reading https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html might help you decide.\n"); + pr_info("Reading https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html might help you decide.\n"); return; } diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 544bd24a9c1e..b0597507bde7 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6801,8 +6801,8 @@ free_partial_vcpu: return ERR_PTR(err); } -#define L1TF_MSG_SMT "L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html for details.\n" -#define L1TF_MSG_L1D "L1TF CPU bug present and virtualization mitigation disabled, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html for details.\n" +#define L1TF_MSG_SMT "L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html for details.\n" +#define L1TF_MSG_L1D "L1TF CPU bug present and virtualization mitigation disabled, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html for details.\n" static int vmx_vm_init(struct kvm *kvm) { -- cgit v1.2.3 From d71eb0ce109a124b0fa714832823b9452f2762cf Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Tue, 2 Apr 2019 09:59:33 -0500 Subject: x86/speculation/mds: Add mds=full,nosmt cmdline option Add the mds=full,nosmt cmdline option. This is like mds=full, but with SMT disabled if the CPU is vulnerable. Signed-off-by: Josh Poimboeuf Signed-off-by: Thomas Gleixner Reviewed-by: Tyler Hicks Acked-by: Jiri Kosina --- Documentation/admin-guide/hw-vuln/mds.rst | 3 +++ Documentation/admin-guide/kernel-parameters.txt | 6 ++++-- arch/x86/kernel/cpu/bugs.c | 10 ++++++++++ 3 files changed, 17 insertions(+), 2 deletions(-) (limited to 'arch') diff --git a/Documentation/admin-guide/hw-vuln/mds.rst b/Documentation/admin-guide/hw-vuln/mds.rst index 1de29d28903d..244ab47d1fb3 100644 --- a/Documentation/admin-guide/hw-vuln/mds.rst +++ b/Documentation/admin-guide/hw-vuln/mds.rst @@ -260,6 +260,9 @@ time with the option "mds=". The valid arguments for this option are: It does not automatically disable SMT. + full,nosmt The same as mds=full, with SMT disabled on vulnerable + CPUs. This is the complete mitigation. + off Disables MDS mitigations completely. ============ ============================================================= diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 7325319c2c23..8f04985d3122 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2372,8 +2372,10 @@ This parameter controls the MDS mitigation. The options are: - full - Enable MDS mitigation on vulnerable CPUs - off - Unconditionally disable MDS mitigation + full - Enable MDS mitigation on vulnerable CPUs + full,nosmt - Enable MDS mitigation and disable + SMT on vulnerable CPUs + off - Unconditionally disable MDS mitigation Not specifying this option is equivalent to mds=full. diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 373ae1dcd301..9f252082a83b 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -221,6 +221,7 @@ static void x86_amd_ssb_disable(void) /* Default mitigation for L1TF-affected CPUs */ static enum mds_mitigations mds_mitigation __ro_after_init = MDS_MITIGATION_FULL; +static bool mds_nosmt __ro_after_init = false; static const char * const mds_strings[] = { [MDS_MITIGATION_OFF] = "Vulnerable", @@ -238,8 +239,13 @@ static void __init mds_select_mitigation(void) if (mds_mitigation == MDS_MITIGATION_FULL) { if (!boot_cpu_has(X86_FEATURE_MD_CLEAR)) mds_mitigation = MDS_MITIGATION_VMWERV; + static_branch_enable(&mds_user_clear); + + if (mds_nosmt && !boot_cpu_has(X86_BUG_MSBDS_ONLY)) + cpu_smt_disable(false); } + pr_info("%s\n", mds_strings[mds_mitigation]); } @@ -255,6 +261,10 @@ static int __init mds_cmdline(char *str) mds_mitigation = MDS_MITIGATION_OFF; else if (!strcmp(str, "full")) mds_mitigation = MDS_MITIGATION_FULL; + else if (!strcmp(str, "full,nosmt")) { + mds_mitigation = MDS_MITIGATION_FULL; + mds_nosmt = true; + } return 0; } -- cgit v1.2.3 From 7c3658b20194a5b3209a143f63bc9c643c6a3ae2 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Tue, 2 Apr 2019 10:00:14 -0500 Subject: x86/speculation: Move arch_smt_update() call to after mitigation decisions arch_smt_update() now has a dependency on both Spectre v2 and MDS mitigations. Move its initial call to after all the mitigation decisions have been made. Signed-off-by: Josh Poimboeuf Signed-off-by: Thomas Gleixner Reviewed-by: Tyler Hicks Acked-by: Jiri Kosina --- arch/x86/kernel/cpu/bugs.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 9f252082a83b..3f934ffef8cf 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -111,6 +111,8 @@ void __init check_bugs(void) mds_select_mitigation(); + arch_smt_update(); + #ifdef CONFIG_X86_32 /* * Check whether we are able to run this kernel safely on SMP. @@ -638,9 +640,6 @@ specv2_set_mode: /* Set up IBPB and STIBP depending on the general spectre V2 command */ spectre_v2_user_select_mitigation(cmd); - - /* Enable STIBP if appropriate */ - arch_smt_update(); } static void update_stibp_msr(void * __unused) -- cgit v1.2.3 From 39226ef02bfb43248b7db12a4fdccb39d95318e3 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Tue, 2 Apr 2019 10:00:51 -0500 Subject: x86/speculation/mds: Add SMT warning message MDS is vulnerable with SMT. Make that clear with a one-time printk whenever SMT first gets enabled. Signed-off-by: Josh Poimboeuf Signed-off-by: Thomas Gleixner Reviewed-by: Tyler Hicks Acked-by: Jiri Kosina --- arch/x86/kernel/cpu/bugs.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 3f934ffef8cf..22a14d4b68a2 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -673,6 +673,9 @@ static void update_indir_branch_cond(void) static_branch_disable(&switch_to_cond_stibp); } +#undef pr_fmt +#define pr_fmt(fmt) fmt + /* Update the static key controlling the MDS CPU buffer clear in idle */ static void update_mds_branch_idle(void) { @@ -693,6 +696,8 @@ static void update_mds_branch_idle(void) static_branch_disable(&mds_idle_clear); } +#define MDS_MSG_SMT "MDS CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html for more details.\n" + void arch_smt_update(void) { /* Enhanced IBRS implies STIBP. No update required. */ @@ -717,6 +722,8 @@ void arch_smt_update(void) switch (mds_mitigation) { case MDS_MITIGATION_FULL: case MDS_MITIGATION_VMWERV: + if (sched_smt_active() && !boot_cpu_has(X86_BUG_MSBDS_ONLY)) + pr_warn_once(MDS_MSG_SMT); update_mds_branch_idle(); break; case MDS_MITIGATION_OFF: @@ -1149,6 +1156,7 @@ static int __init l1tf_cmdline(char *str) early_param("l1tf", l1tf_cmdline); #undef pr_fmt +#define pr_fmt(fmt) fmt #ifdef CONFIG_SYSFS -- cgit v1.2.3 From cae5ec342645746d617dd420d206e1588d47768a Mon Sep 17 00:00:00 2001 From: Boris Ostrovsky Date: Fri, 12 Apr 2019 17:50:57 -0400 Subject: x86/speculation/mds: Fix comment s/L1TF/MDS/ Signed-off-by: Boris Ostrovsky Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Thomas Gleixner Reviewed-by: Tyler Hicks Reviewed-by: Josh Poimboeuf --- arch/x86/kernel/cpu/bugs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 22a14d4b68a2..0642505dda69 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -221,7 +221,7 @@ static void x86_amd_ssb_disable(void) #undef pr_fmt #define pr_fmt(fmt) "MDS: " fmt -/* Default mitigation for L1TF-affected CPUs */ +/* Default mitigation for MDS-affected CPUs */ static enum mds_mitigations mds_mitigation __ro_after_init = MDS_MITIGATION_FULL; static bool mds_nosmt __ro_after_init = false; -- cgit v1.2.3 From e2c3c94788b08891dcf3dbe608f9880523ecd71b Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk Date: Fri, 12 Apr 2019 17:50:58 -0400 Subject: x86/speculation/mds: Print SMT vulnerable on MSBDS with mitigations off This code is only for CPUs which are affected by MSBDS, but are *not* affected by the other two MDS issues. For such CPUs, enabling the mds_idle_clear mitigation is enough to mitigate SMT. However if user boots with 'mds=off' and still has SMT enabled, we should not report that SMT is mitigated: $cat /sys//devices/system/cpu/vulnerabilities/mds Vulnerable; SMT mitigated But rather: Vulnerable; SMT vulnerable Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Thomas Gleixner Reviewed-by: Tyler Hicks Reviewed-by: Josh Poimboeuf Link: https://lkml.kernel.org/r/20190412215118.294906495@localhost.localdomain --- arch/x86/kernel/cpu/bugs.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 0642505dda69..6b8a55c7cebc 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1204,7 +1204,8 @@ static ssize_t mds_show_state(char *buf) if (boot_cpu_has(X86_BUG_MSBDS_ONLY)) { return sprintf(buf, "%s; SMT %s\n", mds_strings[mds_mitigation], - sched_smt_active() ? "mitigated" : "disabled"); + (mds_mitigation == MDS_MITIGATION_OFF ? "vulnerable" : + sched_smt_active() ? "mitigated" : "disabled")); } return sprintf(buf, "%s; SMT %s\n", mds_strings[mds_mitigation], -- cgit v1.2.3 From 5c14068f87d04adc73ba3f41c2a303d3c3d1fa12 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Wed, 17 Apr 2019 16:39:02 -0500 Subject: x86/speculation/mds: Add 'mitigations=' support for MDS Add MDS to the new 'mitigations=' cmdline option. Signed-off-by: Josh Poimboeuf Signed-off-by: Thomas Gleixner --- Documentation/admin-guide/kernel-parameters.txt | 2 ++ arch/x86/kernel/cpu/bugs.c | 5 +++-- 2 files changed, 5 insertions(+), 2 deletions(-) (limited to 'arch') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 9aa3543a8723..18cad2b0392a 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2556,6 +2556,7 @@ spectre_v2_user=off [X86] spec_store_bypass_disable=off [X86,PPC] l1tf=off [X86] + mds=off [X86] auto (default) Mitigate all CPU vulnerabilities, but leave SMT @@ -2570,6 +2571,7 @@ if needed. This is for users who always want to be fully mitigated, even if it means losing SMT. Equivalent to: l1tf=flush,nosmt [X86] + mds=full,nosmt [X86] mminit_loglevel= [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 3c5c3c3ba734..667c273a66d7 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -233,7 +233,7 @@ static const char * const mds_strings[] = { static void __init mds_select_mitigation(void) { - if (!boot_cpu_has_bug(X86_BUG_MDS)) { + if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off()) { mds_mitigation = MDS_MITIGATION_OFF; return; } @@ -244,7 +244,8 @@ static void __init mds_select_mitigation(void) static_branch_enable(&mds_user_clear); - if (mds_nosmt && !boot_cpu_has(X86_BUG_MSBDS_ONLY)) + if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) && + (mds_nosmt || cpu_mitigations_auto_nosmt())) cpu_smt_disable(false); } -- cgit v1.2.3