[PATCH] arm64: Advertise mitigation of Spectre-v2, or lack thereof

[PATCH] arm64: Advertise mitigation of Spectre-v2, or lack thereof

[Marc Zyngier]

We currently have a list of CPUs affected by Spectre-v2, for which
we check that the firmware implements ARCH_WORKAROUND_1. It turns
out that not all firmwares do implement the required mitigation,
and that we fail to let the user know about it.

Instead, let's slightly revamp our checks, and let the user know
the status of the mitigation in the kernel log.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm64/kernel/cpu_errata.c | 82 +++++++++++++++++-----------------
 1 file changed, 41 insertions(+), 41 deletions(-)

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index a509e35132d2..3a79088cbc22 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -182,15 +182,6 @@ static void  install_bp_hardening_cb(const struct arm64_cpu_capabilities *entry,
 				     const char *hyp_vecs_start,
 				     const char *hyp_vecs_end)
 {
-	u64 pfr0;
-
-	if (!entry->matches(entry, SCOPE_LOCAL_CPU))
-		return;
-
-	pfr0 = read_cpuid(ID_AA64PFR0_EL1);
-	if (cpuid_feature_extract_unsigned_field(pfr0, ID_AA64PFR0_CSV2_SHIFT))
-		return;
-
 	__install_bp_hardening_cb(fn, hyp_vecs_start, hyp_vecs_end);
 }
 
@@ -220,26 +211,51 @@ static void qcom_link_stack_sanitization(void)
 		     : "=&r" (tmp));
 }
 
-static void
-enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
+/*
+ * List of CPUs where we need to issue a psci call to
+ * harden the branch predictor.
+ */
+static const struct midr_range arm64_bp_harden_smccc_cpus[] = {
+	MIDR_ALL_VERSIONS(MIDR_CORTEX_A57),
+	MIDR_ALL_VERSIONS(MIDR_CORTEX_A72),
+	MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
+	MIDR_ALL_VERSIONS(MIDR_CORTEX_A75),
+	MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
+	MIDR_ALL_VERSIONS(MIDR_CAVIUM_THUNDERX2),
+	MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR_V1),
+	MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR),
+	MIDR_ALL_VERSIONS(MIDR_NVIDIA_DENVER),
+	{},
+};
+
+static bool
+has_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry,
+			    int scope)
 {
 	bp_hardening_cb_t cb;
 	void *smccc_start, *smccc_end;
 	struct arm_smccc_res res;
 	u32 midr = read_cpuid_id();
 
-	if (!entry->matches(entry, SCOPE_LOCAL_CPU))
-		return;
+	if (WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible()))
+		return false;
+
+	if (cpuid_feature_extract_unsigned_field(read_cpuid(ID_AA64PFR0_EL1),
+						 ID_AA64PFR0_CSV2_SHIFT))
+		return false;
+	
+	if (!is_midr_in_range_list(midr, arm64_bp_harden_smccc_cpus))
+		return false;
 
 	if (psci_ops.smccc_version == SMCCC_VERSION_1_0)
-		return;
+		goto fail;
 
 	switch (psci_ops.conduit) {
 	case PSCI_CONDUIT_HVC:
 		arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
 				  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
 		if ((int)res.a0 < 0)
-			return;
+			goto fail;
 		cb = call_hvc_arch_workaround_1;
 		/* This is a guest, no need to patch KVM vectors */
 		smccc_start = NULL;
@@ -250,14 +266,14 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
 		arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
 				  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
 		if ((int)res.a0 < 0)
-			return;
+			goto fail;
 		cb = call_smc_arch_workaround_1;
 		smccc_start = __smccc_workaround_1_smc_start;
 		smccc_end = __smccc_workaround_1_smc_end;
 		break;
 
 	default:
-		return;
+		goto fail;
 	}
 
 	if (((midr & MIDR_CPU_MODEL_MASK) == MIDR_QCOM_FALKOR) ||
@@ -266,7 +282,11 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
 
 	install_bp_hardening_cb(entry, cb, smccc_start, smccc_end);
 
-	return;
+	return true;
+
+fail:
+	pr_warn_once("ARM_SMCCC_ARCH_WORKAROUND_1 missing from firmware\n");
+	return false;
 }
 #endif	/* CONFIG_HARDEN_BRANCH_PREDICTOR */
 
@@ -539,27 +559,6 @@ multi_entry_cap_cpu_enable(const struct arm64_cpu_capabilities *entry)
 			caps->cpu_enable(caps);
 }
 
-#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
-
-/*
- * List of CPUs where we need to issue a psci call to
- * harden the branch predictor.
- */
-static const struct midr_range arm64_bp_harden_smccc_cpus[] = {
-	MIDR_ALL_VERSIONS(MIDR_CORTEX_A57),
-	MIDR_ALL_VERSIONS(MIDR_CORTEX_A72),
-	MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
-	MIDR_ALL_VERSIONS(MIDR_CORTEX_A75),
-	MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
-	MIDR_ALL_VERSIONS(MIDR_CAVIUM_THUNDERX2),
-	MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR_V1),
-	MIDR_ALL_VERSIONS(MIDR_QCOM_FALKOR),
-	MIDR_ALL_VERSIONS(MIDR_NVIDIA_DENVER),
-	{},
-};
-
-#endif
-
 #ifdef CONFIG_HARDEN_EL2_VECTORS
 
 static const struct midr_range arm64_harden_el2_vectors[] = {
@@ -712,9 +711,10 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 #endif
 #ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
 	{
+		.desc = "Branch predictor hardening",
 		.capability = ARM64_HARDEN_BRANCH_PREDICTOR,
-		.cpu_enable = enable_smccc_arch_workaround_1,
-		ERRATA_MIDR_RANGE_LIST(arm64_bp_harden_smccc_cpus),
+		.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
+		.matches = has_smccc_arch_workaround_1,
 	},
 #endif
 #ifdef CONFIG_HARDEN_EL2_VECTORS
-- 
2.19.2


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