KVM: arm/arm64: Add save/restore support for firmware workaround state

KVM implements the firmware interface for mitigating cache speculation
vulnerabilities. Guests may use this interface to ensure mitigation is
active.
If we want to migrate such a guest to a host with a different support
level for those workarounds, migration might need to fail, to ensure that
critical guests don't loose their protection.

Introduce a way for userland to save and restore the workarounds state.
On restoring we do checks that make sure we don't downgrade our
mitigation level.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm/include/asm/kvm_emulate.h

@@ -271,6 +271,16 @@ static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
 	return vcpu_cp15(vcpu, c0_MPIDR) & MPIDR_HWID_BITMASK;
 }
 
+static inline bool kvm_arm_get_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu)
+{
+	return false;
+}
+
+static inline void kvm_arm_set_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu,
+						      bool flag)
+{
+}
+
 static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
 {
 	*vcpu_cpsr(vcpu) |= PSR_E_BIT;

arch/arm/include/uapi/asm/kvm.h

@@ -214,6 +214,18 @@ struct kvm_vcpu_events {
 #define KVM_REG_ARM_FW_REG(r)		(KVM_REG_ARM | KVM_REG_SIZE_U64 | \
 					 KVM_REG_ARM_FW | ((r) & 0xffff))
 #define KVM_REG_ARM_PSCI_VERSION	KVM_REG_ARM_FW_REG(0)
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1	KVM_REG_ARM_FW_REG(1)
+	/* Higher values mean better protection. */
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL		0
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL		1
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_REQUIRED	2
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2	KVM_REG_ARM_FW_REG(2)
+	/* Higher values mean better protection. */
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL		0
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN		1
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL		2
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED	3
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED	(1U << 4)
 
 /* Device Control API: ARM VGIC */
 #define KVM_DEV_ARM_VGIC_GRP_ADDR	0

arch/arm64/include/asm/kvm_emulate.h

@@ -353,6 +353,20 @@ static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
 	return vcpu_read_sys_reg(vcpu, MPIDR_EL1) & MPIDR_HWID_BITMASK;
 }
 
+static inline bool kvm_arm_get_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu)
+{
+	return vcpu->arch.workaround_flags & VCPU_WORKAROUND_2_FLAG;
+}
+
+static inline void kvm_arm_set_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu,
+						      bool flag)
+{
+	if (flag)
+		vcpu->arch.workaround_flags |= VCPU_WORKAROUND_2_FLAG;
+	else
+		vcpu->arch.workaround_flags &= ~VCPU_WORKAROUND_2_FLAG;
+}
+
 static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
 {
 	if (vcpu_mode_is_32bit(vcpu)) {

arch/arm64/include/uapi/asm/kvm.h

@@ -229,6 +229,16 @@ struct kvm_vcpu_events {
 #define KVM_REG_ARM_FW_REG(r)		(KVM_REG_ARM64 | KVM_REG_SIZE_U64 | \
 					 KVM_REG_ARM_FW | ((r) & 0xffff))
 #define KVM_REG_ARM_PSCI_VERSION	KVM_REG_ARM_FW_REG(0)
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1	KVM_REG_ARM_FW_REG(1)
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL		0
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL		1
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_REQUIRED	2
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2	KVM_REG_ARM_FW_REG(2)
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL		0
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN		1
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL		2
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED	3
+#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED     	(1U << 4)
 
 /* SVE registers */
 #define KVM_REG_ARM64_SVE		(0x15 << KVM_REG_ARM_COPROC_SHIFT)

virt/kvm/arm/psci.c

@@ -438,43 +438,104 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 
 int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
 {
-	return 1;		/* PSCI version */
+	return 3;		/* PSCI version and two workaround registers */
 }
 
 int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
 {
-	if (put_user(KVM_REG_ARM_PSCI_VERSION, uindices))
+	if (put_user(KVM_REG_ARM_PSCI_VERSION, uindices++))
+		return -EFAULT;
+
+	if (put_user(KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1, uindices++))
+		return -EFAULT;
+
+	if (put_user(KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2, uindices++))
 		return -EFAULT;
 
 	return 0;
 }
 
-int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
+#define KVM_REG_FEATURE_LEVEL_WIDTH	4
+#define KVM_REG_FEATURE_LEVEL_MASK	(BIT(KVM_REG_FEATURE_LEVEL_WIDTH) - 1)
+
+/*
+ * Convert the workaround level into an easy-to-compare number, where higher
+ * values mean better protection.
+ */
+static int get_kernel_wa_level(u64 regid)
 {
-	if (reg->id == KVM_REG_ARM_PSCI_VERSION) {
-		void __user *uaddr = (void __user *)(long)reg->addr;
-		u64 val;
-
-		val = kvm_psci_version(vcpu, vcpu->kvm);
-		if (copy_to_user(uaddr, &val, KVM_REG_SIZE(reg->id)))
-			return -EFAULT;
-
-		return 0;
+	switch (regid) {
+	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
+		switch (kvm_arm_harden_branch_predictor()) {
+		case KVM_BP_HARDEN_UNKNOWN:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL;
+		case KVM_BP_HARDEN_WA_NEEDED:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL;
+		case KVM_BP_HARDEN_NOT_REQUIRED:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_REQUIRED;
+		}
+		return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL;
+	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
+		switch (kvm_arm_have_ssbd()) {
+		case KVM_SSBD_FORCE_DISABLE:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
+		case KVM_SSBD_KERNEL:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL;
+		case KVM_SSBD_FORCE_ENABLE:
+		case KVM_SSBD_MITIGATED:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED;
+		case KVM_SSBD_UNKNOWN:
+		default:
+			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN;
+		}
 	}
 
 	return -EINVAL;
 }
 
+int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
+{
+	void __user *uaddr = (void __user *)(long)reg->addr;
+	u64 val;
+
+	switch (reg->id) {
+	case KVM_REG_ARM_PSCI_VERSION:
+		val = kvm_psci_version(vcpu, vcpu->kvm);
+		break;
+	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
+		val = get_kernel_wa_level(reg->id) & KVM_REG_FEATURE_LEVEL_MASK;
+		break;
+	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
+		val = get_kernel_wa_level(reg->id) & KVM_REG_FEATURE_LEVEL_MASK;
+
+		if (val == KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL &&
+		    kvm_arm_get_vcpu_workaround_2_flag(vcpu))
+			val |= KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED;
+		break;
+	default:
+		return -ENOENT;
+	}
+
+	if (copy_to_user(uaddr, &val, KVM_REG_SIZE(reg->id)))
+		return -EFAULT;
+
+	return 0;
+}
+
 int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 {
-	if (reg->id == KVM_REG_ARM_PSCI_VERSION) {
 	void __user *uaddr = (void __user *)(long)reg->addr;
-		bool wants_02;
 	u64 val;
+	int wa_level;
 
 	if (copy_from_user(&val, uaddr, KVM_REG_SIZE(reg->id)))
 		return -EFAULT;
 
+	switch (reg->id) {
+	case KVM_REG_ARM_PSCI_VERSION:
+	{
+		bool wants_02;
+
 		wants_02 = test_bit(KVM_ARM_VCPU_PSCI_0_2, vcpu->arch.features);
 
 		switch (val) {
@@ -490,6 +551,54 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 			vcpu->kvm->arch.psci_version = val;
 			return 0;
 		}
+		break;
+	}
+
+	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
+		if (val & ~KVM_REG_FEATURE_LEVEL_MASK)
+			return -EINVAL;
+
+		if (get_kernel_wa_level(reg->id) < val)
+			return -EINVAL;
+
+		return 0;
+
+	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
+		if (val & ~(KVM_REG_FEATURE_LEVEL_MASK |
+			    KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED))
+			return -EINVAL;
+
+		wa_level = val & KVM_REG_FEATURE_LEVEL_MASK;
+
+		if (get_kernel_wa_level(reg->id) < wa_level)
+			return -EINVAL;
+
+		/* The enabled bit must not be set unless the level is AVAIL. */
+		if (wa_level != KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL &&
+		    wa_level != val)
+			return -EINVAL;
+
+		/* Are we finished or do we need to check the enable bit ? */
+		if (kvm_arm_have_ssbd() != KVM_SSBD_KERNEL)
+			return 0;
+
+		/*
+		 * If this kernel supports the workaround to be switched on
+		 * or off, make sure it matches the requested setting.
+		 */
+		switch (wa_level) {
+		case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL:
+			kvm_arm_set_vcpu_workaround_2_flag(vcpu,
+			    val & KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED);
+			break;
+		case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED:
+			kvm_arm_set_vcpu_workaround_2_flag(vcpu, true);
+			break;
+		}
+
+		return 0;
+	default:
+		return -ENOENT;
 	}
 
 	return -EINVAL;