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: v5.10.241~455
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=eaf108b66d454547560e0964af4db9613f9e7df9;p=thirdparty%2Fkernel%2Fstable.git

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

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: 78192f511f40 ("x86/bugs: Add a Transient Scheduler Attacks mitigation")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index e67d7603449b7..bf07b2c5418a0 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -599,6 +599,8 @@ 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) {