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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 <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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4
Documentation/kernel-parameters.txt
View File

@ -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)

23
arch/x86/kernel/cpu/common.c
View File

@ -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);