linux-kernel - [PATCH v3 29/35] x86/bugs: Add attack vector controls for retbleed

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Message-ID: <20250108202515.385902-30-david.kaplan@amd.com>
Date: Wed, 8 Jan 2025 14:25:09 -0600
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 29/35] x86/bugs: Add attack vector controls for retbleed

Use attack vector controls to determine if retbleed mitigation is
required.

Disable SMT if cross-thread protection is desired and STIBP is not
available.

Signed-off-by: David Kaplan <david.kaplan@....com>
---
 arch/x86/kernel/cpu/bugs.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 41c8a9dad411..430f89a5f66a 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1331,13 +1331,17 @@ static void __init retbleed_select_mitigation(void)
 	}
 
 	if (retbleed_mitigation == RETBLEED_MITIGATION_AUTO) {
-		if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
-		    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
-			if (IS_ENABLED(CONFIG_MITIGATION_UNRET_ENTRY))
-				retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
-			else if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY) &&
-				 boot_cpu_has(X86_FEATURE_IBPB))
-				retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
+		if (should_mitigate_vuln(X86_BUG_RETBLEED)) {
+			if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
+			    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
+				if (IS_ENABLED(CONFIG_MITIGATION_UNRET_ENTRY))
+					retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
+				else if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY) &&
+					 boot_cpu_has(X86_FEATURE_IBPB))
+					retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
+			}
+		} else {
+			retbleed_mitigation = RETBLEED_MITIGATION_NONE;
 		}
 	}
 }
@@ -1438,7 +1442,8 @@ static void __init retbleed_apply_mitigation(void)
 	}
 
 	if (mitigate_smt && !boot_cpu_has(X86_FEATURE_STIBP) &&
-	    (retbleed_nosmt || cpu_mitigations_auto_nosmt()))
+	    (retbleed_nosmt || cpu_mitigations_auto_nosmt() ||
+	     cpu_mitigate_attack_vector(CPU_MITIGATE_CROSS_THREAD)))
 		cpu_smt_disable(false);
 
 }
-- 
2.34.1