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Commit de5397ad authored by Fenghua Yu's avatar Fenghua Yu Committed by H. Peter Anvin
Browse files

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: default avatarFenghua Yu <fenghua.yu@intel.com>
LKML-Reference: <1305157865-31727-1-git-send-email-fenghua.yu@intel.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent dc23c0bc

Documentation/kernel-parameters.txt

+4 −0
Original line number Diff line number Diff line
@@ -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)

arch/x86/kernel/cpu/common.c

+23 −0
Original line number Diff line number Diff line
@@ -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);