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authorFenghua Yu <fenghua.yu@intel.com>2011-05-11 16:51:05 -0700
committerH. Peter Anvin <hpa@linux.intel.com>2011-05-17 21:22:00 -0700
commitde5397ad5b9ad22e2401c4dacdf1bb3b19c05679 (patch)
treee8c612c4f84efe458d8ec3c23f1bfd834f20c0f2
parentdc23c0bccf5eea171c87b3db285d032b9a5f06c4 (diff)
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>
-rw-r--r--Documentation/kernel-parameters.txt4
-rw-r--r--arch/x86/kernel/cpu/common.c23
2 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index cc85a92..56fb8c1 100644
--- a/Documentation/kernel-parameters.txt
+++ b/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)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 173f3a3..cbc70a2 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/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);