KVM: arm/arm64: vgic: Return error on incompatible uaccess GICD_IIDR writes

If userspace attempts to write a GICD_IIDR that does not match the
kernel version, return an error to userspace.  The intention is to allow
implementation changes inside KVM while avoiding silently breaking
migration resulting in guests not running without any clear indication
of what went wrong.
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

virt/kvm/arm/vgic/vgic-mmio-v2.c

@@ -75,6 +75,20 @@ static void vgic_mmio_write_v2_misc(struct kvm_vcpu *vcpu,
 	}
 }
 
+static int vgic_mmio_uaccess_write_v2_misc(struct kvm_vcpu *vcpu,
+					   gpa_t addr, unsigned int len,
+					   unsigned long val)
+{
+	switch (addr & 0x0c) {
+	case GIC_DIST_IIDR:
+		if (val != vgic_mmio_read_v2_misc(vcpu, addr, len))
+			return -EINVAL;
+	}
+
+	vgic_mmio_write_v2_misc(vcpu, addr, len, val);
+	return 0;
+}
+
 static void vgic_mmio_write_sgir(struct kvm_vcpu *source_vcpu,
 				 gpa_t addr, unsigned int len,
 				 unsigned long val)
@@ -367,9 +381,10 @@ static void vgic_mmio_write_apr(struct kvm_vcpu *vcpu,
 }
 
 static const struct vgic_register_region vgic_v2_dist_registers[] = {
-	REGISTER_DESC_WITH_LENGTH(GIC_DIST_CTRL,
-		vgic_mmio_read_v2_misc, vgic_mmio_write_v2_misc, 12,
-		VGIC_ACCESS_32bit),
+	REGISTER_DESC_WITH_LENGTH_UACCESS(GIC_DIST_CTRL,
+		vgic_mmio_read_v2_misc, vgic_mmio_write_v2_misc,
+		NULL, vgic_mmio_uaccess_write_v2_misc,
+		12, VGIC_ACCESS_32bit),
 	REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_IGROUP,
 		vgic_mmio_read_raz, vgic_mmio_write_wi, NULL, NULL, 1,
 		VGIC_ACCESS_32bit),

virt/kvm/arm/vgic/vgic-mmio-v3.c

@@ -113,6 +113,20 @@ static void vgic_mmio_write_v3_misc(struct kvm_vcpu *vcpu,
 	}
 }
 
+static int vgic_mmio_uaccess_write_v3_misc(struct kvm_vcpu *vcpu,
+					   gpa_t addr, unsigned int len,
+					   unsigned long val)
+{
+	switch (addr & 0x0c) {
+	case GICD_IIDR:
+		if (val != vgic_mmio_read_v3_misc(vcpu, addr, len))
+			return -EINVAL;
+	}
+
+	vgic_mmio_write_v3_misc(vcpu, addr, len, val);
+	return 0;
+}
+
 static unsigned long vgic_mmio_read_irouter(struct kvm_vcpu *vcpu,
 					    gpa_t addr, unsigned int len)
 {
@@ -449,9 +463,10 @@ static void vgic_mmio_write_pendbase(struct kvm_vcpu *vcpu,
 	}
 
 static const struct vgic_register_region vgic_v3_dist_registers[] = {
-	REGISTER_DESC_WITH_LENGTH(GICD_CTLR,
-		vgic_mmio_read_v3_misc, vgic_mmio_write_v3_misc, 16,
-		VGIC_ACCESS_32bit),
+	REGISTER_DESC_WITH_LENGTH_UACCESS(GICD_CTLR,
+		vgic_mmio_read_v3_misc, vgic_mmio_write_v3_misc,
+		NULL, vgic_mmio_uaccess_write_v3_misc,
+		16, VGIC_ACCESS_32bit),
 	REGISTER_DESC_WITH_LENGTH(GICD_STATUSR,
 		vgic_mmio_read_rao, vgic_mmio_write_wi, 4,
 		VGIC_ACCESS_32bit),