FAILED: patch "[PATCH] x86/CPU/AMD: Add RDSEED fix for Zen5" failed to apply to 6.12-stable tree

FAILED: patch "[PATCH] x86/CPU/AMD: Add RDSEED fix for Zen5" failed to apply to 6.12-stable tree

[gregkh]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 607b9fb2ce248cc5b633c5949e0153838992c152
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025110202-attendant-curtain-cd04@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 607b9fb2ce248cc5b633c5949e0153838992c152 Mon Sep 17 00:00:00 2001
From: Gregory Price <gourry@gourry.net>
Date: Mon, 20 Oct 2025 11:13:55 +0200
Subject: [PATCH] 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

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index ccaa51ce63f6..bc29be670a2a 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)

Re: FAILED: patch "[PATCH] x86/CPU/AMD: Add RDSEED fix for Zen5" failed to apply to 6.12-stable tree

[Borislav Petkov]

On Sun, Nov 02, 2025 at 11:19:02PM +0900, gregkh@linuxfoundation.org wrote:
> +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),
> +};

Yeah, we don't have that min microcode gunk with the device_id match so we'll
have to do something like we did for TSA. I.e., below.

I'll test it tomorrow to make sure it doesn't do any cat incinerations :-P

---

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 18518a481016..437c1db652e9 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1018,14 +1018,39 @@ 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 bool check_rdseed_microcode(void)
+{
+	struct cpuinfo_x86 *c = &boot_cpu_data;
+	union zen_patch_rev p;
+	u32 min_rev = 0;
+
+	p.ext_fam	= c->x86 - 0xf;
+	p.model		= c->x86_model;
+	p.ext_model	= c->x86_model >> 4;
+	p.stepping	= c->x86_stepping;
+	/* reserved bits are expected to be 0 in test below */
+	p.__reserved	= 0;
+
+	if (cpu_has(c, X86_FEATURE_ZEN5)) {
+		switch (p.ucode_rev >> 8) {
+		case 0xb0021:	min_rev = 0xb00215a; break;
+		case 0xb1010:	min_rev = 0xb101054; break;
+		default:
+			pr_debug("%s: ucode_rev: 0x%x, current revision: 0x%x\n",
+				 __func__, p.ucode_rev, c->microcode);
+			return false;
+		}
+	}
+
+	if (!min_rev)
+		return false;
+
+	return c->microcode >= min_rev;
+}
 
 static void init_amd_zen5(struct cpuinfo_x86 *c)
 {
-	if (!x86_match_min_microcode_rev(zen5_rdseed_microcode)) {
+	if (!check_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");

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: FAILED: patch "[PATCH] x86/CPU/AMD: Add RDSEED fix for Zen5" failed to apply to 6.12-stable tree

[Greg KH]

On Sun, Nov 02, 2025 at 06:31:01PM +0100, Borislav Petkov wrote:
> On Sun, Nov 02, 2025 at 11:19:02PM +0900, gregkh@linuxfoundation.org wrote:
> > +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),
> > +};
> 
> Yeah, we don't have that min microcode gunk with the device_id match so we'll
> have to do something like we did for TSA. I.e., below.
> 
> I'll test it tomorrow to make sure it doesn't do any cat incinerations :-P

No worries.  Don't know if you want this for any other stable kernels
older than that, but it didn't apply there either :)

thanks,

greg k-h

Re: FAILED: patch "[PATCH] x86/CPU/AMD: Add RDSEED fix for Zen5" failed to apply to 6.12-stable tree

[Borislav Petkov]

On Mon, Nov 03, 2025 at 09:21:54AM +0900, Greg KH wrote:
> No worries.  Don't know if you want this for any other stable kernels
> older than that, but it didn't apply there either :)

Yeah, something even older running Zen5...? Meh, I'll say "no need" and
I betcha someone would promptly crawl out of the woodwork, hand'a'raisin'...

:-P

Let's see what actually happens.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

[PATCH 6.12] x86/CPU/AMD: Add RDSEED fix for Zen5

[Borislav Petkov]

From: Gregory Price <gourry@gourry.net>
Subject: [PATCH] x86/CPU/AMD: Add RDSEED fix for Zen5

Commit 607b9fb2ce248cc5b633c5949e0153838992c152 upstream.

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. ]
  [ bp: 6.12 backport: use the alternative microcode version checking. ]

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 | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 4810271302d0..437c1db652e9 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1018,8 +1018,43 @@ static void init_amd_zen4(struct cpuinfo_x86 *c)
 	}
 }
 
+static bool check_rdseed_microcode(void)
+{
+	struct cpuinfo_x86 *c = &boot_cpu_data;
+	union zen_patch_rev p;
+	u32 min_rev = 0;
+
+	p.ext_fam	= c->x86 - 0xf;
+	p.model		= c->x86_model;
+	p.ext_model	= c->x86_model >> 4;
+	p.stepping	= c->x86_stepping;
+	/* reserved bits are expected to be 0 in test below */
+	p.__reserved	= 0;
+
+	if (cpu_has(c, X86_FEATURE_ZEN5)) {
+		switch (p.ucode_rev >> 8) {
+		case 0xb0021:	min_rev = 0xb00215a; break;
+		case 0xb1010:	min_rev = 0xb101054; break;
+		default:
+			pr_debug("%s: ucode_rev: 0x%x, current revision: 0x%x\n",
+				 __func__, p.ucode_rev, c->microcode);
+			return false;
+		}
+	}
+
+	if (!min_rev)
+		return false;
+
+	return c->microcode >= min_rev;
+}
+
 static void init_amd_zen5(struct cpuinfo_x86 *c)
 {
+	if (!check_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)
-- 
2.51.0


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette