The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 607b9fb2ce248cc5b633c5949e0153838992c152 Gitweb: https://git.kernel.org/tip/607b9fb2ce248cc5b633c5949e0153838992c152 Author: Gregory Price gourry@gourry.net AuthorDate: Mon, 20 Oct 2025 11:13:55 +02:00 Committer: Borislav Petkov (AMD) bp@alien8.de CommitterDate: Tue, 28 Oct 2025 12:37:49 +01:00

x86/CPU/AMD: Add RDSEED fix for Zen5

There's an issue with RDSEED's 16-bit and 32-bit register output variants on Zen5 which return a random value of 0 "at a rate inconsistent with randomness while incorrectly signaling success (CF=1)". Search the web for AMD-SB-7055 for more detail.

Add a fix glue which checks microcode revisions.

[ bp: Add microcode revisions checking, rewrite. ]

Cc: stable@vger.kernel.org Signed-off-by: Gregory Price gourry@gourry.net Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Link: https://lore.kernel.org/r/20251018024010.4112396-1-gourry@gourry.net --- arch/x86/kernel/cpu/amd.c | 10 ++++++++++ 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index ccaa51c..bc29be6 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -1035,8 +1035,18 @@ static void init_amd_zen4(struct cpuinfo_x86 *c) } }

+static const struct x86_cpu_id zen5_rdseed_microcode[] = { + ZEN_MODEL_STEP_UCODE(0x1a, 0x02, 0x1, 0x0b00215a), + ZEN_MODEL_STEP_UCODE(0x1a, 0x11, 0x0, 0x0b101054), +}; + static void init_amd_zen5(struct cpuinfo_x86 *c) { + if (!x86_match_min_microcode_rev(zen5_rdseed_microcode)) { + clear_cpu_cap(c, X86_FEATURE_RDSEED); + msr_clear_bit(MSR_AMD64_CPUID_FN_7, 18); + pr_emerg_once("RDSEED32 is broken. Disabling the corresponding CPUID bit.\n"); + } }

static void init_amd(struct cpuinfo_x86 *c)