From: Borislav Petkov (AMD) Date: Tue, 7 Apr 2026 09:40:03 +0000 (+0200) Subject: x86/CPU: Fix FPDSS on Zen1 X-Git-Tag: v6.1.169~1 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=1272cfedf4cd1019ddf583917a99b62f2d3645bb;p=thirdparty%2Fkernel%2Fstable.git x86/CPU: Fix FPDSS on Zen1 commit e55d98e7756135f32150b9b8f75d580d0d4b2dd3 upstream. 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) Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index 749e7fe245e65..5b8268afc0358 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -580,6 +580,9 @@ #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 2d71c329b3475..1ba9fcfde6d20 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -1051,6 +1051,9 @@ static void init_amd_zn(struct cpuinfo_x86 *c) if (c->x86 == 0x19 && !cpu_has(c, X86_FEATURE_BTC_NO)) set_cpu_cap(c, X86_FEATURE_BTC_NO); } + + 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 bool cpu_has_zenbleed_microcode(void)