From d0281a257f370b09c410e466571858b4e12869c9 Mon Sep 17 00:00:00 2001 From: Fenghua Yu Date: Tue, 17 May 2011 18:44:26 -0700 Subject: x86, cpufeature: Add cpufeature flag for SMEP Add support for newly documented SMEP (Supervisor Mode Execution Protection) CPU feature flag. SMEP prevents the CPU in kernel-mode to jump to an executable page that has the user flag set in the PTE. This prevents the kernel from executing user-space code accidentally or maliciously, so it for example prevents kernel exploits from jumping to specially prepared user-mode shell code. [ hpa: added better description by Ingo Molnar ] Signed-off-by: Fenghua Yu LKML-Reference: <1305683069-25394-2-git-send-email-fenghua.yu@intel.com> Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/cpufeature.h | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index 7f2f7b123293..8808cdb96c3f 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -195,6 +195,7 @@ /* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */ #define X86_FEATURE_FSGSBASE (9*32+ 0) /* {RD/WR}{FS/GS}BASE instructions*/ +#define X86_FEATURE_SMEP (9*32+ 7) /* Supervisor Mode Execution Protection */ #define X86_FEATURE_ERMS (9*32+ 9) /* Enhanced REP MOVSB/STOSB */ #if defined(__KERNEL__) && !defined(__ASSEMBLY__) -- cgit v1.2.3 From dc23c0bccf5eea171c87b3db285d032b9a5f06c4 Mon Sep 17 00:00:00 2001 From: Fenghua Yu Date: Tue, 17 May 2011 18:44:27 -0700 Subject: x86, cpu: Add SMEP CPU feature in CR4 Add support for newly documented SMEP (Supervisor Mode Execution Protection) CPU feature in CR4. Signed-off-by: Fenghua Yu LKML-Reference: <1305683069-25394-3-git-send-email-fenghua.yu@intel.com> Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/processor-flags.h | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/include/asm/processor-flags.h b/arch/x86/include/asm/processor-flags.h index a898a2b6e10c..59ab4dffa377 100644 --- a/arch/x86/include/asm/processor-flags.h +++ b/arch/x86/include/asm/processor-flags.h @@ -60,6 +60,7 @@ #define X86_CR4_OSXMMEXCPT 0x00000400 /* enable unmasked SSE exceptions */ #define X86_CR4_VMXE 0x00002000 /* enable VMX virtualization */ #define X86_CR4_OSXSAVE 0x00040000 /* enable xsave and xrestore */ +#define X86_CR4_SMEP 0x00100000 /* enable SMEP support */ /* * x86-64 Task Priority Register, CR8 -- cgit v1.2.3 From de5397ad5b9ad22e2401c4dacdf1bb3b19c05679 Mon Sep 17 00:00:00 2001 From: Fenghua Yu Date: Wed, 11 May 2011 16:51:05 -0700 Subject: x86, cpu: Enable/disable Supervisor Mode Execution Protection Enable/disable newly documented SMEP (Supervisor Mode Execution Protection) CPU feature in kernel. CR4.SMEP (bit 20) is 0 at power-on. If the feature is supported by CPU (X86_FEATURE_SMEP), enable SMEP by setting CR4.SMEP. New kernel option nosmep disables the feature even if the feature is supported by CPU. [ hpa: moved the call to setup_smep() until after the vendor-specific initialization; that ensures that CPUID features are unmasked. We will still run it before we have userspace (never mind uncontrolled userspace). ] Signed-off-by: Fenghua Yu LKML-Reference: <1305157865-31727-1-git-send-email-fenghua.yu@intel.com> Signed-off-by: H. Peter Anvin --- Documentation/kernel-parameters.txt | 4 ++++ arch/x86/kernel/cpu/common.c | 23 +++++++++++++++++++++++ 2 files changed, 27 insertions(+) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index cc85a9278190..56fb8c16e20b 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -1664,6 +1664,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted. noexec=on: enable non-executable mappings (default) noexec=off: disable non-executable mappings + nosmep [X86] + Disable SMEP (Supervisor Mode Execution Protection) + even if it is supported by processor. + noexec32 [X86-64] This affects only 32-bit executables. noexec32=on: enable non-executable mappings (default) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 173f3a3fa1a6..cbc70a27430c 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -254,6 +254,25 @@ static inline void squash_the_stupid_serial_number(struct cpuinfo_x86 *c) } #endif +static int disable_smep __initdata; +static __init int setup_disable_smep(char *arg) +{ + disable_smep = 1; + return 1; +} +__setup("nosmep", setup_disable_smep); + +static __init void setup_smep(struct cpuinfo_x86 *c) +{ + if (cpu_has(c, X86_FEATURE_SMEP)) { + if (unlikely(disable_smep)) { + setup_clear_cpu_cap(X86_FEATURE_SMEP); + clear_in_cr4(X86_CR4_SMEP); + } else + set_in_cr4(X86_CR4_SMEP); + } +} + /* * Some CPU features depend on higher CPUID levels, which may not always * be available due to CPUID level capping or broken virtualization @@ -667,6 +686,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c) c->cpu_index = 0; #endif filter_cpuid_features(c, false); + + setup_smep(c); } void __init early_cpu_init(void) @@ -752,6 +773,8 @@ static void __cpuinit generic_identify(struct cpuinfo_x86 *c) #endif } + setup_smep(c); + get_model_name(c); /* Default name */ detect_nopl(c); -- cgit v1.2.3