[tip: x86/urgent] x86/bugs: Fix GDS mitigation selecting when mitigation is off
From: tip-bot2 for Li RongQing
Date: Tue Aug 19 2025 - 05:14:20 EST
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: d4932a1b148bb6121121e56bad312c4339042d70
Gitweb: https://git.kernel.org/tip/d4932a1b148bb6121121e56bad312c4339042d70
Author: Li RongQing <lirongqing@xxxxxxxxx>
AuthorDate: Tue, 19 Aug 2025 10:33:56 +08:00
Committer: Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Tue, 19 Aug 2025 10:38:04 +02:00
x86/bugs: Fix GDS mitigation selecting when mitigation is off
The current GDS mitigation logic incorrectly returns early when the
attack vector mitigation is turned off, which leads to two problems:
1. CPUs without ARCH_CAP_GDS_CTRL support are incorrectly marked with
GDS_MITIGATION_OFF when they should be marked as
GDS_MITIGATION_UCODE_NEEDED.
2. The mitigation state checks and locking verification that follow are
skipped, which means:
- fail to detect if the mitigation was locked
- miss the warning when trying to disable a locked mitigation
Remove the early return to ensure proper mitigation state handling. This
allows:
- Proper mitigation classification for non-ARCH_CAP_GDS_CTRL CPUs
- Complete mitigation state verification
This also addresses the failed MSR 0x123 write attempt at boot on
non-ARCH_CAP_GDS_CTRL CPUs:
unchecked MSR access error: WRMSR to 0x123 (tried to write 0x0000000000000010) at rIP: ... (update_gds_msr)
Call Trace:
identify_secondary_cpu
start_secondary
common_startup_64
WARNING: CPU: 1 PID: 0 at arch/x86/kernel/cpu/bugs.c:1053 update_gds_msr
[ bp: Massage, zap superfluous braces. ]
Fixes: 8c7261abcb7ad ("x86/bugs: Add attack vector controls for GDS")
Suggested-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/20250819023356.2012-1-lirongqing@xxxxxxxxx
---
arch/x86/kernel/cpu/bugs.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 2186a77..49ef1b8 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1068,10 +1068,8 @@ static void __init gds_select_mitigation(void)
if (gds_mitigation == GDS_MITIGATION_AUTO) {
if (should_mitigate_vuln(X86_BUG_GDS))
gds_mitigation = GDS_MITIGATION_FULL;
- else {
+ else
gds_mitigation = GDS_MITIGATION_OFF;
- return;
- }
}
/* No microcode */