arm64: Rewrite Spectre-v2 mitigation code

The Spectre-v2 mitigation code is pretty unwieldy and hard to maintain.
This is largely due to it being written hastily, without much clue as to
how things would pan out, and also because it ends up mixing policy and
state in such a way that it is very difficult to figure out what's going
on.

Rewrite the Spectre-v2 mitigation so that it clearly separates state from
policy and follows a more structured approach to handling the mitigation.

Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 3 insertions, 233 deletions

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 5eb9a9126dc4..4103391f51b5 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -106,145 +106,6 @@ cpu_enable_trap_ctr_access(const struct arm64_cpu_capabilities *cap)
 		sysreg_clear_set(sctlr_el1, SCTLR_EL1_UCT, 0);
 }
 
-atomic_t arm64_el2_vector_last_slot = ATOMIC_INIT(-1);
-
-#include <asm/mmu_context.h>
-#include <asm/cacheflush.h>
-
-DEFINE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);
-
-#ifdef CONFIG_RANDOMIZE_BASE
-static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start,
-				const char *hyp_vecs_end)
-{
-	void *dst = lm_alias(__bp_harden_hyp_vecs + slot * SZ_2K);
-	int i;
-
-	for (i = 0; i < SZ_2K; i += 0x80)
-		memcpy(dst + i, hyp_vecs_start, hyp_vecs_end - 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)
-{
-	static DEFINE_RAW_SPINLOCK(bp_lock);
-	int cpu, slot = -1;
-	const char *hyp_vecs_start = __smccc_workaround_1_smc;
-	const char *hyp_vecs_end = __smccc_workaround_1_smc +
-				   __SMCCC_WORKAROUND_1_SMC_SZ;
-
-	/*
-	 * detect_harden_bp_fw() passes NULL for the hyp_vecs start/end if
-	 * we're a guest. Skip the hyp-vectors work.
-	 */
-	if (!is_hyp_mode_available()) {
-		__this_cpu_write(bp_hardening_data.fn, fn);
-		return;
-	}
-
-	raw_spin_lock(&bp_lock);
-	for_each_possible_cpu(cpu) {
-		if (per_cpu(bp_hardening_data.fn, cpu) == fn) {
-			slot = per_cpu(bp_hardening_data.hyp_vectors_slot, cpu);
-			break;
-		}
-	}
-
-	if (slot == -1) {
-		slot = atomic_inc_return(&arm64_el2_vector_last_slot);
-		BUG_ON(slot >= BP_HARDEN_EL2_SLOTS);
-		__copy_hyp_vect_bpi(slot, hyp_vecs_start, hyp_vecs_end);
-	}
-
-	__this_cpu_write(bp_hardening_data.hyp_vectors_slot, slot);
-	__this_cpu_write(bp_hardening_data.fn, fn);
-	raw_spin_unlock(&bp_lock);
-}
-#else
-static void install_bp_hardening_cb(bp_hardening_cb_t fn)
-{
-	__this_cpu_write(bp_hardening_data.fn, fn);
-}
-#endif	/* CONFIG_RANDOMIZE_BASE */
-
-#include <linux/arm-smccc.h>
-
-static void __maybe_unused call_smc_arch_workaround_1(void)
-{
-	arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
-}
-
-static void call_hvc_arch_workaround_1(void)
-{
-	arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
-}
-
-static void qcom_link_stack_sanitization(void)
-{
-	u64 tmp;
-
-	asm volatile("mov	%0, x30		\n"
-		     ".rept	16		\n"
-		     "bl	. + 4		\n"
-		     ".endr			\n"
-		     "mov	x30, %0		\n"
-		     : "=&r" (tmp));
-}
-
-static bool __nospectre_v2;
-static int __init parse_nospectre_v2(char *str)
-{
-	__nospectre_v2 = true;
-	return 0;
-}
-early_param("nospectre_v2", parse_nospectre_v2);
-
-/*
- * -1: No workaround
- *  0: No workaround required
- *  1: Workaround installed
- */
-static int detect_harden_bp_fw(void)
-{
-	bp_hardening_cb_t cb;
-	struct arm_smccc_res res;
-	u32 midr = read_cpuid_id();
-
-	arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
-			     ARM_SMCCC_ARCH_WORKAROUND_1, &res);
-
-	switch ((int)res.a0) {
-	case 1:
-		/* Firmware says we're just fine */
-		return 0;
-	case 0:
-		break;
-	default:
-		return -1;
-	}
-
-	switch (arm_smccc_1_1_get_conduit()) {
-	case SMCCC_CONDUIT_HVC:
-		cb = call_hvc_arch_workaround_1;
-		break;
-
-	case SMCCC_CONDUIT_SMC:
-		cb = call_smc_arch_workaround_1;
-		break;
-
-	default:
-		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(cb);
-	return 1;
-}
-
 DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);
 
 int ssbd_state __read_mostly = ARM64_SSBD_KERNEL;
@@ -508,83 +369,6 @@ cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused)
 	.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,			\
 	CAP_MIDR_RANGE_LIST(midr_list)
 
-/* Track overall mitigation state. We are only mitigated if all cores are ok */
-static bool __hardenbp_enab = true;
-static bool __spectrev2_safe = true;
-
-int get_spectre_v2_workaround_state(void)
-{
-	if (__spectrev2_safe)
-		return ARM64_BP_HARDEN_NOT_REQUIRED;
-
-	if (!__hardenbp_enab)
-		return ARM64_BP_HARDEN_UNKNOWN;
-
-	return ARM64_BP_HARDEN_WA_NEEDED;
-}
-
-/*
- * 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),
-	MIDR_ALL_VERSIONS(MIDR_BRAHMA_B53),
-	MIDR_ALL_VERSIONS(MIDR_HISI_TSV110),
-	MIDR_ALL_VERSIONS(MIDR_QCOM_KRYO_3XX_SILVER),
-	MIDR_ALL_VERSIONS(MIDR_QCOM_KRYO_4XX_SILVER),
-	{ /* sentinel */ }
-};
-
-/*
- * Track overall bp hardening for all heterogeneous cores in the machine.
- * We are only considered "safe" if all booted cores are known safe.
- */
-static bool __maybe_unused
-check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
-{
-	int need_wa;
-
-	WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
-
-	/* 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;
-
-	/* 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;
-
-	/* forced off */
-	if (__nospectre_v2 || cpu_mitigations_off()) {
-		pr_info_once("spectrev2 mitigation disabled by command line option\n");
-		__hardenbp_enab = false;
-		return false;
-	}
-
-	if (need_wa < 0) {
-		pr_warn_once("ARM_SMCCC_ARCH_WORKAROUND_1 missing from firmware\n");
-		__hardenbp_enab = false;
-	}
-
-	return (need_wa > 0);
-}
-
-static void
-cpu_enable_branch_predictor_hardening(const struct arm64_cpu_capabilities *cap)
-{
-	cap->matches(cap, SCOPE_LOCAL_CPU);
-}
-
 static const __maybe_unused struct midr_range tx2_family_cpus[] = {
 	MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
 	MIDR_ALL_VERSIONS(MIDR_CAVIUM_THUNDERX2),
@@ -876,11 +660,11 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 	},
 #endif
 	{
-		.desc = "Branch predictor hardening",
+		.desc = "Spectre-v2",
 		.capability = ARM64_SPECTRE_V2,
 		.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
-		.matches = check_branch_predictor,
-		.cpu_enable = cpu_enable_branch_predictor_hardening,
+		.matches = has_spectre_v2,
+		.cpu_enable = spectre_v2_enable_mitigation,
 	},
 #ifdef CONFIG_RANDOMIZE_BASE
 	{
@@ -949,20 +733,6 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 	}
 };
 
-ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
-		char *buf)
-{
-	switch (get_spectre_v2_workaround_state()) {
-	case ARM64_BP_HARDEN_NOT_REQUIRED:
-		return sprintf(buf, "Not affected\n");
-        case ARM64_BP_HARDEN_WA_NEEDED:
-		return sprintf(buf, "Mitigation: Branch predictor hardening\n");
-        case ARM64_BP_HARDEN_UNKNOWN:
-	default:
-		return sprintf(buf, "Vulnerable\n");
-	}
-}
-
 ssize_t cpu_show_spec_store_bypass(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {