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@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250707183316.1349127-13-david.kaplan@amd.com

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 130db820d49d5233bccd2e40b774097de1c95851..de6eb59fd485a4291a660aa1617e48d1ce704e7f 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1313,7 +1313,7 @@ early_param("retbleed", retbleed_parse_cmdline);
 
 static void __init retbleed_select_mitigation(void)
 {
-       if (!boot_cpu_has_bug(X86_BUG_RETBLEED) || cpu_mitigations_off()) {
+       if (!boot_cpu_has_bug(X86_BUG_RETBLEED)) {
                retbleed_mitigation = RETBLEED_MITIGATION_NONE;
                return;
        }
@@ -1350,6 +1350,11 @@ static void __init retbleed_select_mitigation(void)
        if (retbleed_mitigation != RETBLEED_MITIGATION_AUTO)
                return;
 
+       if (!should_mitigate_vuln(X86_BUG_RETBLEED)) {
+               retbleed_mitigation = RETBLEED_MITIGATION_NONE;
+               return;
+       }
+
        /* Intel mitigation selected in retbleed_update_mitigation() */
        if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
            boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
@@ -1373,7 +1378,7 @@ static void __init retbleed_select_mitigation(void)
 
 static void __init retbleed_update_mitigation(void)
 {
-       if (!boot_cpu_has_bug(X86_BUG_RETBLEED) || cpu_mitigations_off())
+       if (!boot_cpu_has_bug(X86_BUG_RETBLEED))
                return;
 
         /* ITS can also enable stuffing */
@@ -1468,7 +1473,7 @@ static void __init retbleed_apply_mitigation(void)
        }
 
        if (mitigate_smt && !boot_cpu_has(X86_FEATURE_STIBP) &&
-           (retbleed_nosmt || cpu_mitigations_auto_nosmt()))
+           (retbleed_nosmt || smt_mitigations == SMT_MITIGATIONS_ON))
                cpu_smt_disable(false);
 }