[PATCH v10 11/12] x86/vmscape: Resolve conflict between attack-vectors and vmscape=force

[Pawan Gupta]

vmscape=force option currently defaults to AUTO mitigation. This lets
attack-vector controls to override the vmscape mitigation. Preventing the
user from being able to force VMSCAPE mitigation.

When vmscape mitigation is forced, allow it be deployed irrespective of
attack vectors. Introduce VMSCAPE_MITIGATION_ON that wins over
attack-vector controls.

Tested-by: Jon Kohler <jon@xxxxxxxxxxx>
Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/bugs.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 1082ed1fb2e6..fbdb137720c4 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -3058,6 +3058,7 @@ static void __init srso_apply_mitigation(void)
 enum vmscape_mitigations {
 	VMSCAPE_MITIGATION_NONE,
 	VMSCAPE_MITIGATION_AUTO,
+	VMSCAPE_MITIGATION_ON,
 	VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER,
 	VMSCAPE_MITIGATION_IBPB_ON_VMEXIT,
 	VMSCAPE_MITIGATION_BHB_CLEAR_EXIT_TO_USER,
@@ -3066,6 +3067,7 @@ enum vmscape_mitigations {
 static const char * const vmscape_strings[] = {
 	[VMSCAPE_MITIGATION_NONE]			= "Vulnerable",
 	/* [VMSCAPE_MITIGATION_AUTO] */
+	/* [VMSCAPE_MITIGATION_ON] */
 	[VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER]		= "Mitigation: IBPB before exit to userspace",
 	[VMSCAPE_MITIGATION_IBPB_ON_VMEXIT]		= "Mitigation: IBPB on VMEXIT",
 	[VMSCAPE_MITIGATION_BHB_CLEAR_EXIT_TO_USER]	= "Mitigation: Clear BHB before exit to userspace",
@@ -3085,7 +3087,7 @@ static int __init vmscape_parse_cmdline(char *str)
 		vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER;
 	} else if (!strcmp(str, "force")) {
 		setup_force_cpu_bug(X86_BUG_VMSCAPE);
-		vmscape_mitigation = VMSCAPE_MITIGATION_AUTO;
+		vmscape_mitigation = VMSCAPE_MITIGATION_ON;
 	} else if (!strcmp(str, "auto")) {
 		vmscape_mitigation = VMSCAPE_MITIGATION_AUTO;
 	} else {
@@ -3117,6 +3119,7 @@ static void __init vmscape_select_mitigation(void)
 		break;
 
 	case VMSCAPE_MITIGATION_AUTO:
+	case VMSCAPE_MITIGATION_ON:
 		/*
 		 * CPUs with BHI_CTRL(ADL and newer) can avoid the IBPB and use
 		 * BHB clear sequence. These CPUs are only vulnerable to the BHI
@@ -3244,6 +3247,7 @@ void cpu_bugs_smt_update(void)
 	switch (vmscape_mitigation) {
 	case VMSCAPE_MITIGATION_NONE:
 	case VMSCAPE_MITIGATION_AUTO:
+	case VMSCAPE_MITIGATION_ON:
 		break;
 	case VMSCAPE_MITIGATION_IBPB_ON_VMEXIT:
 	case VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER:

-- 
2.34.1