Messages in this thread Patch in this message | | | From | "Fenghua Yu" <> | Subject | [PATCH v3 4/4] x86/kernel/cpu/common.c: Disable SMEP by kernel option nosmep | Date | Tue, 17 May 2011 18:44:29 -0700 |
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From: Fenghua Yu <fenghua.yu@intel.com>
SMEP is enabled unconditionally on all CPUs that support it. The nosmep boot option would turn it off shortly afterwards.
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com> --- Documentation/kernel-parameters.txt | 4 ++++ arch/x86/kernel/cpu/common.c | 22 ++++++++++++++++++++++ 2 files changed, 26 insertions(+), 0 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index cc85a92..76c67e5 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 the 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 e2ced00..9dcec58 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -254,6 +254,27 @@ static inline void squash_the_stupid_serial_number(struct cpuinfo_x86 *c) } #endif +static int disable_smep __initdata; + +static __init int setup_nosmep(char *arg) +{ + disable_smep = 1; + return 1; +} +__setup("nosmep", setup_nosmep); + +/* + * If SMEP is supported by the processor, SMEP has been enabled in CR4 earlier. + * But if kernel option "nosmep" is given, we disable SMEP here. + */ +static __init void config_smep(struct cpuinfo_x86 *c) +{ + if (cpu_has(c, X86_FEATURE_SMEP) && disable_smep) { + setup_clear_cpu_cap(X86_FEATURE_SMEP); + clear_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 @@ -737,6 +758,7 @@ static void __cpuinit generic_identify(struct cpuinfo_x86 *c) get_cpu_vendor(c); get_cpu_cap(c); + config_smep(c); if (c->cpuid_level >= 0x00000001) { c->initial_apicid = (cpuid_ebx(1) >> 24) & 0xFF; -- 1.7.2
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