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x86, cpu: Enable/disable Supervisor Mode Execution Protection

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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 <fenghua.yu@intel.com>
LKML-Reference: <1305157865-31727-1-git-send-email-fenghua.yu@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Fenghua Yu
2011-05-11 16:51:05 -07:00
committed by H. Peter Anvin
parent dc23c0bccf
commit de5397ad5b
2 changed files with 27 additions and 0 deletions
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23
arch/x86/kernel/cpu/common.c
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@@ -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);