Commit 52b6179a authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

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: default avatarH. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-10-git-send-email-hpa@linux.intel.com
parent 63bcff2a

Documentation/kernel-parameters.txt

+5 −1
Original line number Diff line number Diff line
@@ -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]

arch/x86/kernel/cpu/common.c

+26 −0
Original line number Diff line number Diff line
@@ -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);