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

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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: 78192f511f ("x86/bugs: Add a Transient Scheduler Attacks mitigation")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Michael Zhivich
2025-07-23 09:40:19 -04:00
committed by Greg Kroah-Hartman
parent 2cf0c4130b
commit eaf108b66d
1 changed files with 2 additions and 0 deletions
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arch/x86/kernel/cpu/amd.c
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@@ -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) {