x86, smap: Turn on Supervisor Mode Access Prevention

[firefly-linux-kernel-4.4.55.git] / arch / x86 / kernel / cpu / common.c

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a5fbc3c5fccc5e60d61d9ec8f1d3f9f60a2a0467..7d35d65941181d4c5db49293ff4f49448451c638 100644 (file)
--- 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);
@@ -1113,7 +1139,8 @@ void syscall_init(void)
 
        /* Flags to clear on syscall */
        wrmsrl(MSR_SYSCALL_MASK,
-              X86_EFLAGS_TF|X86_EFLAGS_DF|X86_EFLAGS_IF|X86_EFLAGS_IOPL);
+              X86_EFLAGS_TF|X86_EFLAGS_DF|X86_EFLAGS_IF|
+              X86_EFLAGS_IOPL|X86_EFLAGS_AC);
 }
 
 unsigned long kernel_eflags;