Add AUTO mitigations for mds/taa/mmio/rfds to create consistent
vulnerability handling.  These AUTO mitigations will be turned into the
appropriate default mitigations in the <vuln>_select_mitigation()
functions.  In a later patch, these will be used with the new attack
vector controls to help select appropriate mitigations.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
 arch/x86/include/asm/processor.h |  1 +
 arch/x86/kernel/cpu/bugs.c       | 20 ++++++++++++++++----
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index c0975815980c..ea4b87b44455 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -754,6 +754,7 @@ extern enum l1tf_mitigations l1tf_mitigation;
 
 enum mds_mitigations {
 	MDS_MITIGATION_OFF,
+	MDS_MITIGATION_AUTO,
 	MDS_MITIGATION_FULL,
 	MDS_MITIGATION_VMWERV,
 };
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 3fd7a2ce11b5..34d55f368bff 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -234,7 +234,7 @@ static void x86_amd_ssb_disable(void)
 
 /* Default mitigation for MDS-affected CPUs */
 static enum mds_mitigations mds_mitigation __ro_after_init =
-	IS_ENABLED(CONFIG_MITIGATION_MDS) ? MDS_MITIGATION_FULL : MDS_MITIGATION_OFF;
+	IS_ENABLED(CONFIG_MITIGATION_MDS) ? MDS_MITIGATION_AUTO : MDS_MITIGATION_OFF;
 static bool mds_nosmt __ro_after_init = false;
 
 static const char * const mds_strings[] = {
@@ -245,6 +245,7 @@ static const char * const mds_strings[] = {
 
 enum taa_mitigations {
 	TAA_MITIGATION_OFF,
+	TAA_MITIGATION_AUTO,
 	TAA_MITIGATION_UCODE_NEEDED,
 	TAA_MITIGATION_VERW,
 	TAA_MITIGATION_TSX_DISABLED,
@@ -252,27 +253,29 @@ enum taa_mitigations {
 
 /* Default mitigation for TAA-affected CPUs */
 static enum taa_mitigations taa_mitigation __ro_after_init =
-	IS_ENABLED(CONFIG_MITIGATION_TAA) ? TAA_MITIGATION_VERW : TAA_MITIGATION_OFF;
+	IS_ENABLED(CONFIG_MITIGATION_TAA) ? TAA_MITIGATION_AUTO : TAA_MITIGATION_OFF;
 
 enum mmio_mitigations {
 	MMIO_MITIGATION_OFF,
+	MMIO_MITIGATION_AUTO,
 	MMIO_MITIGATION_UCODE_NEEDED,
 	MMIO_MITIGATION_VERW,
 };
 
 /* Default mitigation for Processor MMIO Stale Data vulnerabilities */
 static enum mmio_mitigations mmio_mitigation __ro_after_init =
-	IS_ENABLED(CONFIG_MITIGATION_MMIO_STALE_DATA) ? MMIO_MITIGATION_VERW : MMIO_MITIGATION_OFF;
+	IS_ENABLED(CONFIG_MITIGATION_MMIO_STALE_DATA) ?	MMIO_MITIGATION_AUTO : MMIO_MITIGATION_OFF;
 
 enum rfds_mitigations {
 	RFDS_MITIGATION_OFF,
+	RFDS_MITIGATION_AUTO,
 	RFDS_MITIGATION_VERW,
 	RFDS_MITIGATION_UCODE_NEEDED,
 };
 
 /* Default mitigation for Register File Data Sampling */
 static enum rfds_mitigations rfds_mitigation __ro_after_init =
-	IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_VERW : RFDS_MITIGATION_OFF;
+	IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_AUTO : RFDS_MITIGATION_OFF;
 
 static void __init mds_select_mitigation(void)
 {
@@ -281,6 +284,9 @@ static void __init mds_select_mitigation(void)
 		return;
 	}
 
+	if (mds_mitigation == MDS_MITIGATION_AUTO)
+		mds_mitigation = MDS_MITIGATION_FULL;
+
 	if (mds_mitigation == MDS_MITIGATION_FULL) {
 		if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
 			mds_mitigation = MDS_MITIGATION_VMWERV;
@@ -510,6 +516,9 @@ static void __init rfds_select_mitigation(void)
 	if (rfds_mitigation == RFDS_MITIGATION_OFF)
 		return;
 
+	if (rfds_mitigation == RFDS_MITIGATION_AUTO)
+		rfds_mitigation = RFDS_MITIGATION_VERW;
+
 	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
 		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
 	else
@@ -1995,6 +2004,7 @@ void cpu_bugs_smt_update(void)
 		update_mds_branch_idle();
 		break;
 	case MDS_MITIGATION_OFF:
+	case MDS_MITIGATION_AUTO:
 		break;
 	}
 
@@ -2006,6 +2016,7 @@ void cpu_bugs_smt_update(void)
 		break;
 	case TAA_MITIGATION_TSX_DISABLED:
 	case TAA_MITIGATION_OFF:
+	case TAA_MITIGATION_AUTO:
 		break;
 	}
 
@@ -2016,6 +2027,7 @@ void cpu_bugs_smt_update(void)
 			pr_warn_once(MMIO_MSG_SMT);
 		break;
 	case MMIO_MITIGATION_OFF:
+	case MMIO_MITIGATION_AUTO:
 		break;
 	}
 
-- 
2.34.1

On Tue, Nov 05, 2024 at 03:54:23PM -0600, David Kaplan wrote:
> @@ -1995,6 +2004,7 @@ void cpu_bugs_smt_update(void)
>  		update_mds_branch_idle();
>  		break;
>  	case MDS_MITIGATION_OFF:
> +	case MDS_MITIGATION_AUTO:

This implies AUTO and OFF are similar, which is counter intuitive.
While mitigation selection code ...

> +	if (mds_mitigation == MDS_MITIGATION_AUTO)
> +		mds_mitigation = MDS_MITIGATION_FULL;
> +

... indicates that AUTO is equivalent to FULL. So, I think AUTO should be
handled the same way as FULL in cpu_bugs_smt_update() as well.

Same for TAA and MMIO below.

>  		break;
>  	}
>  
> @@ -2006,6 +2016,7 @@ void cpu_bugs_smt_update(void) break;
>  	case TAA_MITIGATION_TSX_DISABLED:
>  	case TAA_MITIGATION_OFF:
> +	case TAA_MITIGATION_AUTO:
>  		break;
>  	}
>  
> @@ -2016,6 +2027,7 @@ void cpu_bugs_smt_update(void)
>  			pr_warn_once(MMIO_MSG_SMT);
>  		break;
>  	case MMIO_MITIGATION_OFF:
> +	case MMIO_MITIGATION_AUTO:
>  		break;
>  	}