x86/CPU/AMD: Make sure EFER[AIBRSE] is set

The AutoIBRS bit gets set only on the BSP as part of determining which
mitigation to enable on AMD. Setting on the APs relies on the
circumstance that the APs get booted through the trampoline and EFER
- the MSR which contains that bit - gets replicated on every AP from the
BSP.

However, this can change in the future and considering the security
implications of this bit not being set on every CPU, make sure it is set
by verifying EFER later in the boot process and on every AP.

Reported-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20230224185257.o3mcmloei5zqu7wa@treble

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 380753b14cab0751310c8bd1e9f1a2970ee39478..dd32dbc7c33ee0eb84ac45875eae7853e9170d70 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -996,6 +996,17 @@ static void init_amd(struct cpuinfo_x86 *c)
                msr_set_bit(MSR_K7_HWCR, MSR_K7_HWCR_IRPERF_EN_BIT);
 
        check_null_seg_clears_base(c);
+
+       /*
+        * Make sure EFER[AIBRSE - Automatic IBRS Enable] is set. The APs are brought up
+        * using the trampoline code and as part of it, MSR_EFER gets prepared there in
+        * order to be replicated onto them. Regardless, set it here again, if not set,
+        * to protect against any future refactoring/code reorganization which might
+        * miss setting this important bit.
+        */
+       if (spectre_v2_in_eibrs_mode(spectre_v2_enabled) &&
+           cpu_has(c, X86_FEATURE_AUTOIBRS))
+               WARN_ON_ONCE(msr_set_bit(MSR_EFER, _EFER_AUTOIBRS));
 }
 
 #ifdef CONFIG_X86_32

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f9d060e71c3eecfc77c7acda99f8e4a4e4b2d27f..182af64387d061294d4883b3b7b752c60aa616fc 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -784,8 +784,7 @@ static int __init nospectre_v1_cmdline(char *str)
 }
 early_param("nospectre_v1", nospectre_v1_cmdline);
 
-static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
-       SPECTRE_V2_NONE;
+enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init = SPECTRE_V2_NONE;
 
 #undef pr_fmt
 #define pr_fmt(fmt)     "RETBleed: " fmt
@@ -1133,13 +1132,6 @@ spectre_v2_parse_user_cmdline(void)
        return SPECTRE_V2_USER_CMD_AUTO;
 }
 
-static inline bool spectre_v2_in_eibrs_mode(enum spectre_v2_mitigation mode)
-{
-       return mode == SPECTRE_V2_EIBRS ||
-              mode == SPECTRE_V2_EIBRS_RETPOLINE ||
-              mode == SPECTRE_V2_EIBRS_LFENCE;
-}
-
 static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode)
 {
        return spectre_v2_in_eibrs_mode(mode) || mode == SPECTRE_V2_IBRS;

diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h
index 57a5349e69548fe8acb6aaaa1da09f38e19eef40..f97b0fe13da805badcb180c4e27a1add8d6ccf1b 100644 (file)
--- a/arch/x86/kernel/cpu/cpu.h
+++ b/arch/x86/kernel/cpu/cpu.h
@@ -83,4 +83,12 @@ unsigned int aperfmperf_get_khz(int cpu);
 extern void x86_spec_ctrl_setup_ap(void);
 extern void update_srbds_msr(void);
 
+extern enum spectre_v2_mitigation spectre_v2_enabled;
+
+static inline bool spectre_v2_in_eibrs_mode(enum spectre_v2_mitigation mode)
+{
+       return mode == SPECTRE_V2_EIBRS ||
+              mode == SPECTRE_V2_EIBRS_RETPOLINE ||
+              mode == SPECTRE_V2_EIBRS_LFENCE;
+}
 #endif /* ARCH_X86_CPU_H */