From: "H. Peter Anvin" <h...@linux.intel.com>
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: H. Peter Anvin <h...@linux.intel.com>
---
Documentation/kernel-parameters.txt | 6 +++++-
arch/x86/kernel/cpu/common.c | 26 ++++++++++++++++++++++++++
2 files changed, 31 insertions(+), 1 deletions(-)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index ad7e2e5..49c5c41 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -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]
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index cd43e52..7d35d65 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -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);
--
1.7.6.5
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