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, 288 insertions, 0 deletions

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index c37bf468e4a4..4f1411b45301 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -17,7 +17,33 @@
  * Authors: Will Deacon <will@kernel.org> and Marc Zyngier <maz@kernel.org>
  */
 
+#include <linux/arm-smccc.h>
+#include <linux/cpu.h>
 #include <linux/device.h>
+#include <linux/prctl.h>
+
+#include <asm/spectre.h>
+#include <asm/traps.h>
+
+/*
+ * We try to ensure that the mitigation state can never change as the result of
+ * onlining a late CPU.
+ */
+static void update_mitigation_state(enum mitigation_state *oldp,
+				    enum mitigation_state new)
+{
+	enum mitigation_state state;
+
+	do {
+		state = READ_ONCE(*oldp);
+		if (new <= state)
+			break;
+
+		/* Userspace almost certainly can't deal with this. */
+		if (WARN_ON(system_capabilities_finalized()))
+			break;
+	} while (cmpxchg_relaxed(oldp, state, new) != state);
+}
 
 /*
  * Spectre v1.
@@ -30,3 +56,265 @@ ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr,
 {
 	return sprintf(buf, "Mitigation: __user pointer sanitization\n");
 }
+
+/*
+ * Spectre v2.
+ *
+ * This one sucks. A CPU is either:
+ *
+ * - Mitigated in hardware and advertised by ID_AA64PFR0_EL1.CSV2.
+ * - Mitigated in hardware and listed in our "safe list".
+ * - Mitigated in software by firmware.
+ * - Mitigated in software by a CPU-specific dance in the kernel.
+ * - Vulnerable.
+ *
+ * It's not unlikely for different CPUs in a big.LITTLE system to fall into
+ * different camps.
+ */
+static enum mitigation_state spectre_v2_state;
+
+static bool __read_mostly __nospectre_v2;
+static int __init parse_spectre_v2_param(char *str)
+{
+	__nospectre_v2 = true;
+	return 0;
+}
+early_param("nospectre_v2", parse_spectre_v2_param);
+
+static bool spectre_v2_mitigations_off(void)
+{
+	bool ret = __nospectre_v2 || cpu_mitigations_off();
+
+	if (ret)
+		pr_info_once("spectre-v2 mitigation disabled by command line option\n");
+
+	return ret;
+}
+
+ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	switch (spectre_v2_state) {
+	case SPECTRE_UNAFFECTED:
+		return sprintf(buf, "Not affected\n");
+	case SPECTRE_MITIGATED:
+		return sprintf(buf, "Mitigation: Branch predictor hardening\n");
+	case SPECTRE_VULNERABLE:
+		fallthrough;
+	default:
+		return sprintf(buf, "Vulnerable\n");
+	}
+}
+
+static enum mitigation_state spectre_v2_get_cpu_hw_mitigation_state(void)
+{
+	u64 pfr0;
+	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 */ }
+	};
+
+	/* If the CPU has CSV2 set, we're safe */
+	pfr0 = read_cpuid(ID_AA64PFR0_EL1);
+	if (cpuid_feature_extract_unsigned_field(pfr0, ID_AA64PFR0_CSV2_SHIFT))
+		return SPECTRE_UNAFFECTED;
+
+	/* Alternatively, we have a list of unaffected CPUs */
+	if (is_midr_in_range_list(read_cpuid_id(), spectre_v2_safe_list))
+		return SPECTRE_UNAFFECTED;
+
+	return SPECTRE_VULNERABLE;
+}
+
+#define SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED	(1)
+
+static enum mitigation_state spectre_v2_get_cpu_fw_mitigation_state(void)
+{
+	int ret;
+	struct arm_smccc_res res;
+
+	arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
+			     ARM_SMCCC_ARCH_WORKAROUND_1, &res);
+
+	ret = res.a0;
+	switch (ret) {
+	case SMCCC_RET_SUCCESS:
+		return SPECTRE_MITIGATED;
+	case SMCCC_ARCH_WORKAROUND_RET_UNAFFECTED:
+		return SPECTRE_UNAFFECTED;
+	default:
+		fallthrough;
+	case SMCCC_RET_NOT_SUPPORTED:
+		return SPECTRE_VULNERABLE;
+	}
+}
+
+bool has_spectre_v2(const struct arm64_cpu_capabilities *entry, int scope)
+{
+	WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
+
+	if (spectre_v2_get_cpu_hw_mitigation_state() == SPECTRE_UNAFFECTED)
+		return false;
+
+	if (spectre_v2_get_cpu_fw_mitigation_state() == SPECTRE_UNAFFECTED)
+		return false;
+
+	return true;
+}
+
+DEFINE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);
+
+enum mitigation_state arm64_get_spectre_v2_state(void)
+{
+	return spectre_v2_state;
+}
+
+#ifdef CONFIG_KVM
+#ifdef CONFIG_RANDOMIZE_BASE
+#include <asm/cacheflush.h>
+#include <asm/kvm_asm.h>
+
+atomic_t arm64_el2_vector_last_slot = ATOMIC_INIT(-1);
+
+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 */
+#endif	/* CONFIG_KVM */
+
+static void 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_sanitisation(void)
+{
+	u64 tmp;
+
+	asm volatile("mov	%0, x30		\n"
+		     ".rept	16		\n"
+		     "bl	. + 4		\n"
+		     ".endr			\n"
+		     "mov	x30, %0		\n"
+		     : "=&r" (tmp));
+}
+
+static enum mitigation_state spectre_v2_enable_fw_mitigation(void)
+{
+	bp_hardening_cb_t cb;
+	enum mitigation_state state;
+
+	state = spectre_v2_get_cpu_fw_mitigation_state();
+	if (state != SPECTRE_MITIGATED)
+		return state;
+
+	if (spectre_v2_mitigations_off())
+		return SPECTRE_VULNERABLE;
+
+	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 SPECTRE_VULNERABLE;
+	}
+
+	install_bp_hardening_cb(cb);
+	return SPECTRE_MITIGATED;
+}
+
+static enum mitigation_state spectre_v2_enable_sw_mitigation(void)
+{
+	u32 midr;
+
+	if (spectre_v2_mitigations_off())
+		return SPECTRE_VULNERABLE;
+
+	midr = read_cpuid_id();
+	if (((midr & MIDR_CPU_MODEL_MASK) != MIDR_QCOM_FALKOR) &&
+	    ((midr & MIDR_CPU_MODEL_MASK) != MIDR_QCOM_FALKOR_V1))
+		return SPECTRE_VULNERABLE;
+
+	install_bp_hardening_cb(qcom_link_stack_sanitisation);
+	return SPECTRE_MITIGATED;
+}
+
+void spectre_v2_enable_mitigation(const struct arm64_cpu_capabilities *__unused)
+{
+	enum mitigation_state state;
+
+	WARN_ON(preemptible());
+
+	state = spectre_v2_get_cpu_hw_mitigation_state();
+	if (state == SPECTRE_VULNERABLE)
+		state = spectre_v2_enable_fw_mitigation();
+	if (state == SPECTRE_VULNERABLE)
+		state = spectre_v2_enable_sw_mitigation();
+
+	update_mitigation_state(&spectre_v2_state, state);
+}