linux-kernel - [PATCH v3 7/7] x86/bugs: Report correct retbleed mitigation status

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Message-ID: <20250915134706.3201818-8-david.kaplan@amd.com>
Date: Mon, 15 Sep 2025 08:47:06 -0500
From: David Kaplan <david.kaplan@....com>
To: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Ingo Molnar
	<mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>
CC: <linux-kernel@...r.kernel.org>
Subject: [PATCH v3 7/7] 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@....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 1f3a20f6fac0..45c9605fc5c3 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;
+			}
 		}
 	}
 
-- 
2.34.1