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>

1 files changed, 4 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index cc85a9278190..56fb8c16e20b 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)