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authorThomas Gleixner <tglx@linutronix.de>2019-03-01 20:21:08 +0100
committerThomas Gleixner <tglx@linutronix.de>2019-03-06 21:52:11 +0100
commite261f209c3666e842fd645a1e31f001c3a26def9 (patch)
treeee6c362e3e906d83f3d14641f67b2bd74fb9449c /arch/x86
parented5194c2732c8084af9fd159c146ea92bf137128 (diff)
downloadlinux-e261f209c3666e842fd645a1e31f001c3a26def9.tar.bz2
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 <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Reviewed-by: Jon Masters <jcm@redhat.com> Tested-by: Jon Masters <jcm@redhat.com>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/include/asm/cpufeatures.h1
-rw-r--r--arch/x86/kernel/cpu/common.c20
2 files changed, 13 insertions, 8 deletions
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;