linux-kernel - [tip: x86/urgent] x86/microcode/AMD: Handle the case of no BIOS microcode

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <175628661509.1920.11512044580147254115.tip-bot2@tip-bot2>
Date: Wed, 27 Aug 2025 09:23:34 -0000
From: "tip-bot2 for Borislav Petkov (AMD)" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: vit.vavra.kh@...il.com, "Borislav Petkov (AMD)" <bp@...en8.de>,
  <stable@...nel.org>, x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: x86/urgent] x86/microcode/AMD: Handle the case of no BIOS microcode

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

Commit-ID:     fcf8239ad6a5de54fa7ce18e464c6b5951b982cb
Gitweb:        https://git.kernel.org/tip/fcf8239ad6a5de54fa7ce18e464c6b5951b982cb
Author:        Borislav Petkov (AMD) <bp@...en8.de>
AuthorDate:    Wed, 20 Aug 2025 11:58:57 +02:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Wed, 27 Aug 2025 10:24:10 +02:00

x86/microcode/AMD: Handle the case of no BIOS microcode

Machines can be shipped without any microcode in the BIOS. Which means,
the microcode patch revision is 0.

Handle that gracefully.

Fixes: 94838d230a6c ("x86/microcode/AMD: Use the family,model,stepping encoded in the patch ID")
Reported-by: Vítek Vávra <vit.vavra.kh@...il.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Cc: <stable@...nel.org>
---
 arch/x86/kernel/cpu/microcode/amd.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 097e393..514f633 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -171,8 +171,28 @@ static int cmp_id(const void *key, const void *elem)
 		return 1;
 }
 
+static u32 cpuid_to_ucode_rev(unsigned int val)
+{
+	union zen_patch_rev p = {};
+	union cpuid_1_eax c;
+
+	c.full = val;
+
+	p.stepping  = c.stepping;
+	p.model     = c.model;
+	p.ext_model = c.ext_model;
+	p.ext_fam   = c.ext_fam;
+
+	return p.ucode_rev;
+}
+
 static bool need_sha_check(u32 cur_rev)
 {
+	if (!cur_rev) {
+		cur_rev = cpuid_to_ucode_rev(bsp_cpuid_1_eax);
+		pr_info_once("No current revision, generating the lowest one: 0x%x\n", cur_rev);
+	}
+
 	switch (cur_rev >> 8) {
 	case 0x80012: return cur_rev <= 0x800126f; break;
 	case 0x80082: return cur_rev <= 0x800820f; break;
@@ -749,8 +769,6 @@ static struct ucode_patch *cache_find_patch(struct ucode_cpu_info *uci, u16 equi
 	n.equiv_cpu = equiv_cpu;
 	n.patch_id  = uci->cpu_sig.rev;
 
-	WARN_ON_ONCE(!n.patch_id);
-
 	list_for_each_entry(p, &microcode_cache, plist)
 		if (patch_cpus_equivalent(p, &n, false))
 			return p;