diff mbox series

[-v2] x86/CPU/AMD: Make sure EFER[AIBRSE] is set

Message ID 20230310162253.GCZAtZXcpK2JK0cFkZ@fat_crate.local (mailing list archive)
State New, archived
Headers show
Series [-v2] x86/CPU/AMD: Make sure EFER[AIBRSE] is set | expand

Commit Message

Borislav Petkov March 10, 2023, 4:22 p.m. UTC 
v2, with feedback addressed, and rediffed ontop of 6.3-rc1:

---
From: "Borislav Petkov (AMD)" <bp@alien8.de>

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>
Link: https://lore.kernel.org/r/20230224185257.o3mcmloei5zqu7wa@treble
---
 arch/x86/kernel/cpu/amd.c  | 11 +++++++++++
 arch/x86/kernel/cpu/bugs.c | 10 +---------
 arch/x86/kernel/cpu/cpu.h  |  8 ++++++++
 3 files changed, 20 insertions(+), 9 deletions(-)

Comments

Dave Hansen March 13, 2023, 3:42 p.m. UTC | #1 
On 3/10/23 08:22, Borislav Petkov wrote:
> 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>
> Link: https://lore.kernel.org/r/20230224185257.o3mcmloei5zqu7wa@treble

Looks sane, thanks for adding the warning:

Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
diff mbox series

Patch

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 380753b14cab..dd32dbc7c33e 100644
--- 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 f9d060e71c3e..182af64387d0 100644
--- 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 57a5349e6954..f97b0fe13da8 100644
--- 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 */