From: Michael Zhivich <mzhivich@akamai.com>
Date: Wed, 23 Jul 2025 13:40:19 +0000 (-0400)
Subject: x86/bugs: Fix use of possibly uninit value in amd_check_tsa_microcode()
X-Git-Tag: archive/raspbian/6.1.147-1+rpi1^2~57
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=e6566b359b3a2284199b4958ec62cbc7cdc06f02;p=linux.git

x86/bugs: Fix use of possibly uninit value in amd_check_tsa_microcode()

Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/commit?id=ab2c2b383f0b1a2a37d06219952f59ed0e88fa02

For kernels compiled with CONFIG_INIT_STACK_NONE=y, the value of __reserved
field in zen_patch_rev union on the stack may be garbage.  If so, it will
prevent correct microcode check when consulting p.ucode_rev, resulting in
incorrect mitigation selection.

This is a stable-only fix.

Cc: <stable@vger.kernel.org>
Signed-off-by: Michael Zhivich <mzhivich@akamai.com>
Fixes: d12145e8454f ("x86/bugs: Add a Transient Scheduler Attacks mitigation")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Gbp-Pq: Topic bugfix/x86
Gbp-Pq: Name x86-bugs-Fix-use-of-possibly-uninit-value-in-amd_che.patch
---

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 4785d41558d..2d71c329b34 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -563,6 +563,8 @@ static bool amd_check_tsa_microcode(void)
 	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 (c->x86 == 0x19) {
 		switch (p.ucode_rev >> 8) {