[v6] Attack vector controls (part 2)

[PATCH v7 19/22] x86/bugs: Add attack vector controls for TSA

Posted by David Kaplan 2 months, 3 weeks ago

Use attack vector controls to determine which TSA mitigation to use.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
 arch/x86/kernel/cpu/bugs.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f41d871f0622..e02b232fcc6e 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1657,28 +1657,38 @@ early_param("tsa", tsa_parse_cmdline);
 
 static void __init tsa_select_mitigation(void)
 {
-	if (cpu_mitigations_off() || !boot_cpu_has_bug(X86_BUG_TSA)) {
+	if (!boot_cpu_has_bug(X86_BUG_TSA)) {
 		tsa_mitigation = TSA_MITIGATION_NONE;
 		return;
 	}
 
+	if (tsa_mitigation == TSA_MITIGATION_AUTO) {
+		if (cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL) ||
+		    cpu_attack_vector_mitigated(CPU_MITIGATE_USER_USER)) {
+			if (cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_HOST) ||
+			    cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_GUEST))
+				tsa_mitigation = TSA_MITIGATION_FULL;
+			else
+				tsa_mitigation = TSA_MITIGATION_USER_KERNEL;
+		} else if (cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_HOST) ||
+			   cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_GUEST)) {
+			tsa_mitigation = TSA_MITIGATION_VM;
+		} else {
+			tsa_mitigation = TSA_MITIGATION_NONE;
+		}
+	}
+
 	if (tsa_mitigation == TSA_MITIGATION_NONE)
 		return;
 
-	if (!boot_cpu_has(X86_FEATURE_VERW_CLEAR)) {
+	if (!boot_cpu_has(X86_FEATURE_VERW_CLEAR))
 		tsa_mitigation = TSA_MITIGATION_UCODE_NEEDED;
-		goto out;
-	}
-
-	if (tsa_mitigation == TSA_MITIGATION_AUTO)
-		tsa_mitigation = TSA_MITIGATION_FULL;
 
 	/*
 	 * No need to set verw_clear_cpu_buf_mitigation_selected - it
 	 * doesn't fit all cases here and it is not needed because this
 	 * is the only VERW-based mitigation on AMD.
 	 */
-out:
 	pr_info("%s\n", tsa_strings[tsa_mitigation]);
 }
 
-- 
2.34.1

[tip: x86/bugs] x86/bugs: Add attack vector controls for TSA

Posted by tip-bot2 for David Kaplan 2 months, 3 weeks ago

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

Commit-ID:     6b21d2f0dc73699e468c877515472c52a5837f8f
Gitweb:        https://git.kernel.org/tip/6b21d2f0dc73699e468c877515472c52a5837f8f
Author:        David Kaplan <david.kaplan@amd.com>
AuthorDate:    Wed, 09 Jul 2025 10:58:44 -05:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Fri, 11 Jul 2025 17:56:41 +02:00

x86/bugs: Add attack vector controls for TSA

Use attack vector controls to determine which TSA mitigation to use.

  [ bp: Simplify the condition in the select function for better
    readability. ]

Signed-off-by: David Kaplan <david.kaplan@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250709155844.3279471-1-david.kaplan@amd.com
---
 arch/x86/kernel/cpu/bugs.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f41d871..b9d0509 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1657,28 +1657,43 @@ early_param("tsa", tsa_parse_cmdline);
 
 static void __init tsa_select_mitigation(void)
 {
-	if (cpu_mitigations_off() || !boot_cpu_has_bug(X86_BUG_TSA)) {
+	if (!boot_cpu_has_bug(X86_BUG_TSA)) {
 		tsa_mitigation = TSA_MITIGATION_NONE;
 		return;
 	}
 
+	if (tsa_mitigation == TSA_MITIGATION_AUTO) {
+		bool vm = false, uk = false;
+
+		tsa_mitigation = TSA_MITIGATION_NONE;
+
+		if (cpu_attack_vector_mitigated(CPU_MITIGATE_USER_KERNEL) ||
+		    cpu_attack_vector_mitigated(CPU_MITIGATE_USER_USER)) {
+			tsa_mitigation = TSA_MITIGATION_USER_KERNEL;
+			uk = true;
+		}
+
+		if (cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_HOST) ||
+		    cpu_attack_vector_mitigated(CPU_MITIGATE_GUEST_GUEST)) {
+			tsa_mitigation = TSA_MITIGATION_VM;
+			vm = true;
+		}
+
+		if (uk && vm)
+			tsa_mitigation = TSA_MITIGATION_FULL;
+	}
+
 	if (tsa_mitigation == TSA_MITIGATION_NONE)
 		return;
 
-	if (!boot_cpu_has(X86_FEATURE_VERW_CLEAR)) {
+	if (!boot_cpu_has(X86_FEATURE_VERW_CLEAR))
 		tsa_mitigation = TSA_MITIGATION_UCODE_NEEDED;
-		goto out;
-	}
-
-	if (tsa_mitigation == TSA_MITIGATION_AUTO)
-		tsa_mitigation = TSA_MITIGATION_FULL;
 
 	/*
 	 * No need to set verw_clear_cpu_buf_mitigation_selected - it
 	 * doesn't fit all cases here and it is not needed because this
 	 * is the only VERW-based mitigation on AMD.
 	 */
-out:
 	pr_info("%s\n", tsa_strings[tsa_mitigation]);
 }