Merge branch 'x86-smep-for-linus' of...

Merge branch 'x86-smep-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'x86-smep-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86, cpu: Enable/disable Supervisor Mode Execution Protection
  x86, cpu: Add SMEP CPU feature in CR4
  x86, cpufeature: Add cpufeature flag for SMEP

Documentation/kernel-parameters.txt

@@ -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/include/asm/cpufeature.h

@@ -195,6 +195,7 @@
 
 /* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
 #define X86_FEATURE_FSGSBASE	(9*32+ 0) /* {RD/WR}{FS/GS}BASE instructions*/
+#define X86_FEATURE_SMEP	(9*32+ 7) /* Supervisor Mode Execution Protection */
 #define X86_FEATURE_ERMS	(9*32+ 9) /* Enhanced REP MOVSB/STOSB */
 
 #if defined(__KERNEL__) && !defined(__ASSEMBLY__)

arch/x86/include/asm/processor-flags.h

@@ -60,6 +60,7 @@
 #define X86_CR4_OSXMMEXCPT 0x00000400 /* enable unmasked SSE exceptions */
 #define X86_CR4_VMXE	0x00002000 /* enable VMX virtualization */
 #define X86_CR4_OSXSAVE 0x00040000 /* enable xsave and xrestore */
+#define X86_CR4_SMEP	0x00100000 /* enable SMEP support */
 
 /*
  * x86-64 Task Priority Register, CR8

arch/x86/kernel/cpu/common.c

@@ -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);