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x86, smap: Turn on Supervisor Mode Access Prevention 

If Supervisor Mode Access Prevention is available and not disabled by
the user, turn it on.  Also fix the expansion of SMEP (Supervisor Mode
Execution Prevention.)

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-10-git-send-email-hpa@linux.intel.com
This commit is contained in:
H. Peter Anvin 2012-09-21 12:43:13 -07:00
parent 63bcff2a30
commit 52b6179ac8
2 changed files with 31 additions and 1 deletions
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6
Documentation/kernel-parameters.txt
View File

@ -1812,8 +1812,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
noexec=on: enable non-executable mappings (default)
noexec=off: disable non-executable mappings
nosmap [X86]
Disable SMAP (Supervisor Mode Access Prevention)
even if it is supported by processor.
nosmep [X86]
Disable SMEP (Supervisor Mode Execution Protection)
Disable SMEP (Supervisor Mode Execution Prevention)
even if it is supported by processor.
noexec32 [X86-64]

26
arch/x86/kernel/cpu/common.c
View File

@ -278,6 +278,31 @@ static __cpuinit void setup_smep(struct cpuinfo_x86 *c)
}
}
static int disable_smap __cpuinitdata;
static __init int setup_disable_smap(char *arg)
{
disable_smap = 1;
return 1;
}
__setup("nosmap", setup_disable_smap);
static __cpuinit void setup_smap(struct cpuinfo_x86 *c)
{
if (cpu_has(c, X86_FEATURE_SMAP)) {
if (unlikely(disable_smap)) {
setup_clear_cpu_cap(X86_FEATURE_SMAP);
clear_in_cr4(X86_CR4_SMAP);
} else {
set_in_cr4(X86_CR4_SMAP);
/*
* Don't use clac() here since alternatives
* haven't run yet...
*/
asm volatile(__stringify(__ASM_CLAC) ::: "memory");
}
}
}
/*
* Some CPU features depend on higher CPUID levels, which may not always
* be available due to CPUID level capping or broken virtualization
@ -713,6 +738,7 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
filter_cpuid_features(c, false);
setup_smep(c);
setup_smap(c);
if (this_cpu->c_bsp_init)
this_cpu->c_bsp_init(c);