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>

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>
Fenghua Yu · H. Peter Anvin
1 parent dc23c0bccf
Showing 2 changed files with 27 additions and 0 deletions Side-by-side Diff
Documentation/kernel-parameters.txt
arch/x86/kernel/cpu/common.c
@@ -1664,6 +1664,10 @@
 			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)
@@ -254,6 +254,25 @@
 }
 #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 @@
 	c->cpu_index = 0;
 #endif
 	filter_cpuid_features(c, false);
+
+	setup_smep(c);
 }
  
 void __init early_cpu_init(void)
@@ -751,6 +772,8 @@
 		c->phys_proc_id = c->initial_apicid;
 #endif
 	}
+
+	setup_smep(c);
  
 	get_model_name(c); /* Default name */
...	...	@@ -1664,6 +1664,10 @@
1664	1664	noexec=on: enable non-executable mappings (default)
1665	1665	noexec=off: disable non-executable mappings
1666	1666
	1667	+ nosmep [X86]
	1668	+ Disable SMEP (Supervisor Mode Execution Protection)
	1669	+ even if it is supported by processor.
	1670	+
1667	1671	noexec32 [X86-64]
1668	1672	This affects only 32-bit executables.
1669	1673	noexec32=on: enable non-executable mappings (default)
...	...	@@ -254,6 +254,25 @@
254	254	}
255	255	#endif
256	256
	257	+static int disable_smep __initdata;
	258	+static __init int setup_disable_smep(char *arg)
	259	+{
	260	+ disable_smep = 1;
	261	+ return 1;
	262	+}
	263	+__setup("nosmep", setup_disable_smep);
	264	+
	265	+static __init void setup_smep(struct cpuinfo_x86 *c)
	266	+{
	267	+ if (cpu_has(c, X86_FEATURE_SMEP)) {
	268	+ if (unlikely(disable_smep)) {
	269	+ setup_clear_cpu_cap(X86_FEATURE_SMEP);
	270	+ clear_in_cr4(X86_CR4_SMEP);
	271	+ } else
	272	+ set_in_cr4(X86_CR4_SMEP);
	273	+ }
	274	+}
	275	+
257	276	/*
258	277	* Some CPU features depend on higher CPUID levels, which may not always
259	278	* be available due to CPUID level capping or broken virtualization
...	...	@@ -667,6 +686,8 @@
667	686	c->cpu_index = 0;
668	687	#endif
669	688	filter_cpuid_features(c, false);
	689	+
	690	+ setup_smep(c);
670	691	}
671	692
672	693	void __init early_cpu_init(void)
...	...	@@ -751,6 +772,8 @@
751	772	c->phys_proc_id = c->initial_apicid;
752	773	#endif
753	774	}
	775	+
	776	+ setup_smep(c);
754	777
755	778	get_model_name(c); /* Default name */
756	779