[PATCH v2 1/2] arm64: Advertise mitigation of Spectre-v2, or lack thereof

[Marc Zyngier <marc.zyngier@arm.com>]

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 rely on a whitelist
of cores that are known to be non-vulnerable, 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 | 111 +++++++++++++++------------------
 1 file changed, 52 insertions(+), 59 deletions(-)

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index c8ff96158b94..145f8b5d093d 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -138,9 +138,9 @@ static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start,
 	__flush_icache_range((uintptr_t)dst, (uintptr_t)dst + SZ_2K);
 }
 
-static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
-				      const char *hyp_vecs_start,
-				      const char *hyp_vecs_end)
+static void install_bp_hardening_cb(bp_hardening_cb_t fn,
+				    const char *hyp_vecs_start,
+				    const char *hyp_vecs_end)
 {
 	static DEFINE_RAW_SPINLOCK(bp_lock);
 	int cpu, slot = -1;
@@ -176,31 +176,14 @@ static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
 #define __smccc_workaround_1_smc_start		NULL
 #define __smccc_workaround_1_smc_end		NULL
 
-static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
-				      const char *hyp_vecs_start,
-				      const char *hyp_vecs_end)
+static void install_bp_hardening_cb(bp_hardening_cb_t fn,
+				    const char *hyp_vecs_start,
+				    const char *hyp_vecs_end)
 {
 	__this_cpu_write(bp_hardening_data.fn, fn);
 }
 #endif	/* CONFIG_KVM_INDIRECT_VECTORS */
 
-static void  install_bp_hardening_cb(const struct arm64_cpu_capabilities *entry,
-				     bp_hardening_cb_t fn,
-				     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);
-}
-
 #include <uapi/linux/psci.h>
 #include <linux/arm-smccc.h>
 #include <linux/psci.h>
@@ -227,20 +210,21 @@ static void qcom_link_stack_sanitization(void)
 		     : "=&r" (tmp));
 }
 
-static void
-enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
+/*
+ * -1: No workaround
+ *  0: No workaround required
+ *  1: Workaround installed
+ */
+static int detect_harden_bp_fw(void)
 {
 	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 (psci_ops.smccc_version == SMCCC_VERSION_1_0) {
 		__hardenbp_enab = false;
-		return;
+		return -1;
 	}
 
 	switch (psci_ops.conduit) {
@@ -249,7 +233,7 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
 				  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
 		if ((int)res.a0 < 0) {
 			__hardenbp_enab = false;
-			return;
+			return -1;
 		}
 		cb = call_hvc_arch_workaround_1;
 		/* This is a guest, no need to patch KVM vectors */
@@ -262,7 +246,7 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
 				  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
 		if ((int)res.a0 < 0) {
 			__hardenbp_enab = false;
-			return;
+			return -1;
 		}
 		cb = call_smc_arch_workaround_1;
 		smccc_start = __smccc_workaround_1_smc_start;
@@ -271,16 +255,22 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
 
 	default:
 		__hardenbp_enab = false;
-		return;
+		return -1;
 	}
 
 	if (((midr & MIDR_CPU_MODEL_MASK) == MIDR_QCOM_FALKOR) ||
 	    ((midr & MIDR_CPU_MODEL_MASK) == MIDR_QCOM_FALKOR_V1))
 		cb = qcom_link_stack_sanitization;
 
-	install_bp_hardening_cb(entry, cb, smccc_start, smccc_end);
+	install_bp_hardening_cb(cb, smccc_start, smccc_end);
 
-	return;
+	return 1;
+}
+#else
+static int detect_harden_bp_fw(void)
+{
+	/* Sorry, can't do a thing */
+	return -1;
 }
 #endif	/* CONFIG_HARDEN_BRANCH_PREDICTOR */
 
@@ -544,7 +534,15 @@ cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused)
 
 #if defined(CONFIG_HARDEN_BRANCH_PREDICTOR) || \
 	defined(CONFIG_GENERIC_CPU_VULNERABILITIES)
-
+/*
+ * List of CPUs that do not need any Spectre-v2 mitigation at all.
+ */
+static const struct midr_range spectre_v2_safe_list[] = {
+	MIDR_ALL_VERSIONS(MIDR_CORTEX_A35),
+	MIDR_ALL_VERSIONS(MIDR_CORTEX_A53),
+	MIDR_ALL_VERSIONS(MIDR_CORTEX_A55),
+	{ /* sentinel */ }
+};
 
 static bool __spectrev2_safe = true;
 
@@ -555,37 +553,34 @@ static bool __spectrev2_safe = true;
 static bool __maybe_unused
 check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
 {
-	bool is_vul;
+	int need_wa;
 
 	WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
 
-	is_vul = is_midr_in_range_list(read_cpuid_id(), entry->midr_range_list);
+	/* If the CPU has CSV2 set, we're safe */
+	if (cpuid_feature_extract_unsigned_field(read_cpuid(ID_AA64PFR0_EL1),
+						 ID_AA64PFR0_CSV2_SHIFT))
+		return false;
 
-	if (is_vul)
-		__spectrev2_safe = false;
+	/* Alternatively, we have a list of unaffected CPUs */
+	if (is_midr_in_range_list(read_cpuid_id(), spectre_v2_safe_list))
+		return false;
+
+	/* Fallback to firmware detection */
+	need_wa = detect_harden_bp_fw();
+	if (!need_wa)
+		return false;
+
+	__spectrev2_safe = false;
+
+	if (need_wa < 0)
+		pr_warn_once("ARM_SMCCC_ARCH_WORKAROUND_1 missing from firmware\n");
 
 	arm64_requested_vuln_attrs |= VULN_SPECTREV2;
 
-	return is_vul;
+	return (need_wa > 0);
 }
 
-/*
- * 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
@@ -764,10 +759,8 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 #ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
 	{
 		.capability = ARM64_HARDEN_BRANCH_PREDICTOR,
-		.cpu_enable = enable_smccc_arch_workaround_1,
 		.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
 		.matches = check_branch_predictor,
-		.midr_range_list = arm64_bp_harden_smccc_cpus,
 	},
 #endif
 #ifdef CONFIG_HARDEN_EL2_VECTORS
-- 
2.20.1