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.
Cc: stable@vger.kernel.org Signed-off-by: Michael Zhivich mzhivich@akamai.com Fixes: 7a0395f6607a5 ("x86/bugs: Add a Transient Scheduler Attacks mitigation") ---
Changes in v2: - Rework patch per feedback - Add Cc: stable
arch/x86/kernel/cpu/amd.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index efd42ee9d1cc..289ff197b1b3 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -378,6 +378,8 @@ 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 (cpu_has(c, X86_FEATURE_ZEN3) || cpu_has(c, X86_FEATURE_ZEN4)) {