From: Gregory Price <gourry@gourry.net>
To: x86@kernel.org
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
hpa@zytor.com, peterz@infradead.org, mario.limonciello@amd.com,
riel@surriel.com, yazen.ghannam@amd.com, me@mixaill.net,
kai.huang@intel.com, sandipan.das@amd.com, darwi@linutronix.de,
stable@kernel.org
Subject: [PATCH] x86/amd: Disable RDSEED on AMD Zen5 Turin because of an error.
Date: Thu, 16 Oct 2025 14:21:07 -0400 [thread overview]
Message-ID: <20251016182107.3496116-1-gourry@gourry.net> (raw)
Under unknown architectural conditions, Zen5 chips running rdseed
can produce (val=0,CF=1) as a "random" result over 10% of the time
(when rdseed is successful). CF=1 indicates success, while val=0
is typically only produced when rdseed fails (CF=0).
This suggests there is an architectural issue which causes rdseed
to misclassify a failure as a success under unknown conditions.
This was reproduced reliably by launching 2-threads per available
core, 1-thread per for hamming on RDSEED, and 1-thread per core
collectively eating and hammering on ~90% of memory.
Fix was modeled after a different RDSEED issue in Zen2 Cyan Skillfish.
Link: https://lore.kernel.org/all/20250715130819.461718765@linuxfoundation.org/
Cc: <stable@kernel.org>
Signed-off-by: Gregory Price <gourry@gourry.net>
---
arch/x86/kernel/cpu/amd.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 5398db4dedb4..9c3b2f010f8c 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1037,6 +1037,12 @@ static void init_amd_zen4(struct cpuinfo_x86 *c)
static void init_amd_zen5(struct cpuinfo_x86 *c)
{
+ /* Disable RDSEED on AMD Turin because of an error. */
+ if (c->x86_model == 0x11 && c->x86_stepping == 0x0) {
+ clear_cpu_cap(c, X86_FEATURE_RDSEED);
+ msr_clear_bit(MSR_AMD64_CPUID_FN_7, 18);
+ pr_emerg("RDSEED is not reliable on this platform; disabling.\n");
+ }
}
static void init_amd(struct cpuinfo_x86 *c)
--
2.51.0
next reply other threads:[~2025-10-16 18:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-16 18:21 Gregory Price [this message]
2025-10-16 19:12 ` [PATCH] x86/amd: Disable RDSEED on AMD Zen5 Turin because of an error Gregory Price
2025-10-16 19:39 ` H. Peter Anvin
2025-10-17 11:48 ` Borislav Petkov
2025-10-17 22:10 ` Jason A. Donenfeld
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