linux-kernel - [PATCH] x86/bugs: Add attack vector controls for VMSCAPE

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Message-ID: <20250912152428.2761154-1-david.kaplan@amd.com>
Date: Fri, 12 Sep 2025 10:24:28 -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] x86/bugs: Add attack vector controls for VMSCAPE

Use attack vector controls to select whether VMSCAPE requires mitigation,
similar to other bugs.

Signed-off-by: David Kaplan <david.kaplan@....com>
---
 .../admin-guide/hw-vuln/attack_vector_controls.rst |  1 +
 arch/x86/kernel/cpu/bugs.c                         | 14 ++++++++++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst b/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
index 5964901d66e3..d0bdbd81dcf9 100644
--- a/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
+++ b/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
@@ -218,6 +218,7 @@ SRSO                  X              X            X              X
 SSB                                  X
 TAA                   X              X            X              X            *       (Note 2)
 TSA                   X              X            X              X
+VMSCAPE                                           X
 =============== ============== ============ ============= ============== ============ ========
 
 Notes:
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 36dcfc5105be..e817bbae0159 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -434,6 +434,9 @@ static bool __init should_mitigate_vuln(unsigned int bug)
 	case X86_BUG_SPEC_STORE_BYPASS:
 		return cpu_attack_vector_mitigated(CPU_MITIGATE_USER_USER);
 
+	case X86_BUG_VMSCAPE:
+		return cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_HOST);
+
 	default:
 		WARN(1, "Unknown bug %x\n", bug);
 		return false;
@@ -3304,15 +3307,18 @@ early_param("vmscape", vmscape_parse_cmdline);
 
 static void __init vmscape_select_mitigation(void)
 {
-	if (cpu_mitigations_off() ||
-	    !boot_cpu_has_bug(X86_BUG_VMSCAPE) ||
+	if (!boot_cpu_has_bug(X86_BUG_VMSCAPE) ||
 	    !boot_cpu_has(X86_FEATURE_IBPB)) {
 		vmscape_mitigation = VMSCAPE_MITIGATION_NONE;
 		return;
 	}
 
-	if (vmscape_mitigation == VMSCAPE_MITIGATION_AUTO)
-		vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER;
+	if (vmscape_mitigation == VMSCAPE_MITIGATION_AUTO) {
+		if (should_mitigate_vuln(X86_BUG_VMSCAPE))
+			vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER;
+		else
+			vmscape_mitigation = VMSCAPE_MITIGATION_NONE;
+	}
 }
 
 static void __init vmscape_update_mitigation(void)

base-commit: 41bab90bbfdc55228b8697d960839a4abb5016d4
-- 
2.34.1