[tip: x86/bugs] x86/bugs: Report correct retbleed mitigation status

["tip-bot2 for David Kaplan" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/bugs branch of tip:

Commit-ID:     930f2361fe542a00de9ce6070b1b6edb976f1165
Gitweb:        https://git.kernel.org/tip/930f2361fe542a00de9ce6070b1b6edb976f1165
Author:        David Kaplan <david.kaplan@amd.com>
AuthorDate:    Mon, 15 Sep 2025 08:47:06 -05:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 16 Sep 2025 13:32:18 +02:00

x86/bugs: Report correct retbleed mitigation status

On Intel CPUs, the default retbleed mitigation is IBRS/eIBRS but this
requires that a similar spectre_v2 mitigation is applied.  If the user
selects a different spectre_v2 mitigation (like spectre_v2=retpoline) a
warning is printed but sysfs will still report 'Mitigation: IBRS' or
'Mitigation: Enhanced IBRS'.  This is incorrect because retbleed is not
mitigated, and IBRS is not actually set.

Fix this by choosing RETBLEED_MITIGATION_NONE in this scenario so the
kernel correctly reports the system as vulnerable to retbleed.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250915134706.3201818-1-david.kaplan@amd.com
---
 arch/x86/kernel/cpu/bugs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 66dbb3b..6a526ae 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1462,8 +1462,10 @@ static void __init retbleed_update_mitigation(void)
 			retbleed_mitigation = RETBLEED_MITIGATION_EIBRS;
 			break;
 		default:
-			if (retbleed_mitigation != RETBLEED_MITIGATION_STUFF)
+			if (retbleed_mitigation != RETBLEED_MITIGATION_STUFF) {
 				pr_err(RETBLEED_INTEL_MSG);
+				retbleed_mitigation = RETBLEED_MITIGATION_NONE;
+			}
 		}
 	}