diff options
| author | Borislav Petkov (AMD) <bp@alien8.de> | 2026-04-07 11:40:03 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-04-17 06:04:42 -0700 |
| commit | e55d98e7756135f32150b9b8f75d580d0d4b2dd3 (patch) | |
| tree | 237ff6781f15dcaf2047a7868a2088b29058312a | |
| parent | 43cfbdda5af60ffc6272a7b8c5c37d1d0a181ca9 (diff) | |
x86/CPU: Fix FPDSS on Zen1
Zen1's hardware divider can leave, under certain circumstances, partial
results from previous operations. Those results can be leaked by
another, attacker thread.
Fix that with a chicken bit.
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | arch/x86/include/asm/msr-index.h | 3 | ||||
| -rw-r--r-- | arch/x86/kernel/cpu/amd.c | 3 |
2 files changed, 6 insertions, 0 deletions
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index 9dc6b610e4e2..a14a0f43e04a 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -674,6 +674,9 @@ #define MSR_AMD64_DC_CFG 0xc0011022 #define MSR_AMD64_TW_CFG 0xc0011023 +#define MSR_AMD64_FP_CFG 0xc0011028 +#define MSR_AMD64_FP_CFG_ZEN1_DENORM_FIX_BIT 9 + #define MSR_AMD64_DE_CFG 0xc0011029 #define MSR_AMD64_DE_CFG_LFENCE_SERIALIZE_BIT 1 #define MSR_AMD64_DE_CFG_LFENCE_SERIALIZE BIT_ULL(MSR_AMD64_DE_CFG_LFENCE_SERIALIZE_BIT) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 33b740c26bef..2d9ae6ab1701 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -944,6 +944,9 @@ static void init_amd_zen1(struct cpuinfo_x86 *c) msr_clear_bit(MSR_K7_HWCR, MSR_K7_HWCR_IRPERF_EN_BIT); clear_cpu_cap(c, X86_FEATURE_IRPERF); } + + pr_notice_once("AMD Zen1 FPDSS bug detected, enabling mitigation.\n"); + msr_set_bit(MSR_AMD64_FP_CFG, MSR_AMD64_FP_CFG_ZEN1_DENORM_FIX_BIT); } static const struct x86_cpu_id amd_zenbleed_microcode[] = { |