x86/speculation: Make "seccomp" the default mode for Speculative Store Bypass

[mirror_ubuntu-artful-kernel.git] / arch / x86 / include / asm / nospec-branch.h

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 5fa86929523b7d90195e890db12779c73dc374d0..5ce68e3e5bc94350fd71fdfbafa1e520ec50e26c 100644 (file)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -166,19 +166,33 @@ enum spectre_v2_mitigation {
 };
 
 /*
- * On VMEXIT we must ensure that no RSB predictions learned in the guest
- * can be followed in the host, by overwriting the RSB completely. Both
- * retpoline and IBRS mitigations for Spectre v2 need this; only on future
- * CPUs with IBRS_ATT *might* it be avoided.
+ * The Intel specification for the SPEC_CTRL MSR requires that we
+ * preserve any already set reserved bits at boot time (e.g. for
+ * future additions that this kernel is not currently aware of).
+ * We then set any additional mitigation bits that we want
+ * ourselves and always use this as the base for SPEC_CTRL.
+ * We also use this when handling guest entry/exit as below.
  */
-static inline void vmexit_fill_RSB(void)
+extern void x86_spec_ctrl_set(u64);
+extern u64 x86_spec_ctrl_get_default(void);
+
+/* The Speculative Store Bypass disable variants */
+enum ssb_mitigation {
+       SPEC_STORE_BYPASS_NONE,
+       SPEC_STORE_BYPASS_DISABLE,
+       SPEC_STORE_BYPASS_PRCTL,
+       SPEC_STORE_BYPASS_SECCOMP,
+};
+
+static __always_inline
+void alternative_msr_write(unsigned int msr, u64 val, unsigned int feature)
 {
-#ifdef CONFIG_RETPOLINE
-       alternative_input("",
-                         "call __fill_rsb",
-                         X86_FEATURE_RETPOLINE,
-                         ASM_NO_INPUT_CLOBBER(_ASM_BX, "memory"));
-#endif
+       asm volatile(ALTERNATIVE("", "wrmsr", %c[feature])
+               : : "c" (msr),
+                   "a" (val),
+                   "d" (val >> 32),
+                   [feature] "i" (feature)
+               : "memory");
 }
 
 #endif /* __ASSEMBLY__ */