linux-kernel - [tip: x86/urgent] x86/bugs: Fix GDS mitigation selecting when mitigation is off

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <175559470048.1420.1064883565288738803.tip-bot2@tip-bot2>
Date: Tue, 19 Aug 2025 09:11:40 -0000
From: "tip-bot2 for Li RongQing" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Li RongQing <lirongqing@...du.com>, "Borislav Petkov (AMD)" <bp@...en8.de>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/bugs: Fix GDS mitigation selecting when
 mitigation is off

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@...du.com>
AuthorDate:    Tue, 19 Aug 2025 10:33:56 +08:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
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@...ux.intel.com>
Signed-off-by: Li RongQing <lirongqing@...du.com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Link: https://lore.kernel.org/20250819023356.2012-1-lirongqing@baidu.com
---
 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 */