KVM: arm64: vgic-v3: Consolidate userspace access for MMIO registers

For userspace accesses to GICv3 MMIO registers (and related data),
vgic_v3_{get,set}_attr are littered with {get,put}_user() calls,
making it hard to audit and reason about.

Consolidate all userspace accesses in vgic_v3_attr_regs_access(),
making the code far simpler to audit.

Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/vgic/vgic-kvm-device.c

@@ -512,18 +512,18 @@ int vgic_v3_parse_attr(struct kvm_device *dev, struct kvm_device_attr *attr,
  *
  * @dev:      kvm device handle
  * @attr:     kvm device attribute
- * @reg:      address the value is read or written, NULL for sysregs
  * @is_write: true if userspace is writing a register
  */
 static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 				    struct kvm_device_attr *attr,
-				    u64 *reg, bool is_write)
+				    bool is_write)
 {
 	struct vgic_reg_attr reg_attr;
 	gpa_t addr;
 	struct kvm_vcpu *vcpu;
+	bool uaccess;
+	u32 val;
 	int ret;
-	u32 tmp32;
 
 	ret = vgic_v3_parse_attr(dev, attr, &reg_attr);
 	if (ret)
@@ -532,6 +532,21 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 	vcpu = reg_attr.vcpu;
 	addr = reg_attr.addr;
 
+	switch (attr->group) {
+	case KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS:
+		/* Sysregs uaccess is performed by the sysreg handling code */
+		uaccess = false;
+		break;
+	default:
+		uaccess = true;
+	}
+
+	if (uaccess && is_write) {
+		u32 __user *uaddr = (u32 __user *)(unsigned long)attr->addr;
+		if (get_user(val, uaddr))
+			return -EFAULT;
+	}
+
 	mutex_lock(&dev->kvm->lock);
 
 	if (unlikely(!vgic_initialized(dev->kvm))) {
@@ -546,20 +561,10 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 
 	switch (attr->group) {
 	case KVM_DEV_ARM_VGIC_GRP_DIST_REGS:
-		if (is_write)
+		ret = vgic_v3_dist_uaccess(vcpu, is_write, addr, &val);
-			tmp32 = *reg;
-
-		ret = vgic_v3_dist_uaccess(vcpu, is_write, addr, &tmp32);
-		if (!is_write)
-			*reg = tmp32;
 		break;
 	case KVM_DEV_ARM_VGIC_GRP_REDIST_REGS:
-		if (is_write)
+		ret = vgic_v3_redist_uaccess(vcpu, is_write, addr, &val);
-			tmp32 = *reg;
-
-		ret = vgic_v3_redist_uaccess(vcpu, is_write, addr, &tmp32);
-		if (!is_write)
-			*reg = tmp32;
 		break;
 	case KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS:
 		ret = vgic_v3_cpu_sysregs_uaccess(vcpu, attr, is_write);
@@ -570,14 +575,10 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 		info = (attr->attr & KVM_DEV_ARM_VGIC_LINE_LEVEL_INFO_MASK) >>
 			KVM_DEV_ARM_VGIC_LINE_LEVEL_INFO_SHIFT;
 		if (info == VGIC_LEVEL_INFO_LINE_LEVEL) {
-			if (is_write)
-				tmp32 = *reg;
 			intid = attr->attr &
 				KVM_DEV_ARM_VGIC_LINE_LEVEL_INTID_MASK;
 			ret = vgic_v3_line_level_info_uaccess(vcpu, is_write,
-							      intid, &tmp32);
+							      intid, &val);
-			if (!is_write)
-				*reg = tmp32;
 		} else {
 			ret = -EINVAL;
 		}
@@ -591,6 +592,12 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,
 	unlock_all_vcpus(dev->kvm);
 out:
 	mutex_unlock(&dev->kvm->lock);
+
+	if (!ret && uaccess && !is_write) {
+		u32 __user *uaddr = (u32 __user *)(unsigned long)attr->addr;
+		ret = put_user(val, uaddr);
+	}
+
 	return ret;
 }
 
@@ -605,30 +612,12 @@ static int vgic_v3_set_attr(struct kvm_device *dev,
 
 	switch (attr->group) {
 	case KVM_DEV_ARM_VGIC_GRP_DIST_REGS:
-	case KVM_DEV_ARM_VGIC_GRP_REDIST_REGS: {
+	case KVM_DEV_ARM_VGIC_GRP_REDIST_REGS:
-		u32 __user *uaddr = (u32 __user *)(long)attr->addr;
+		return vgic_v3_attr_regs_access(dev, attr, true);
-		u32 tmp32;
-		u64 reg;
-
-		if (get_user(tmp32, uaddr))
-			return -EFAULT;
-
-		reg = tmp32;
-		return vgic_v3_attr_regs_access(dev, attr, &reg, true);
-	}
 	case KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS:
-		return vgic_v3_attr_regs_access(dev, attr, NULL, true);
+		return vgic_v3_attr_regs_access(dev, attr, true);
-	case KVM_DEV_ARM_VGIC_GRP_LEVEL_INFO: {
+	case KVM_DEV_ARM_VGIC_GRP_LEVEL_INFO:
-		u32 __user *uaddr = (u32 __user *)(long)attr->addr;
+		return vgic_v3_attr_regs_access(dev, attr, true);
-		u64 reg;
-		u32 tmp32;
-
-		if (get_user(tmp32, uaddr))
-			return -EFAULT;
-
-		reg = tmp32;
-		return vgic_v3_attr_regs_access(dev, attr, &reg, true);
-	}
 	case KVM_DEV_ARM_VGIC_GRP_CTRL: {
 		int ret;
 
@@ -662,30 +651,12 @@ static int vgic_v3_get_attr(struct kvm_device *dev,
 
 	switch (attr->group) {
 	case KVM_DEV_ARM_VGIC_GRP_DIST_REGS:
-	case KVM_DEV_ARM_VGIC_GRP_REDIST_REGS: {
+	case KVM_DEV_ARM_VGIC_GRP_REDIST_REGS:
-		u32 __user *uaddr = (u32 __user *)(long)attr->addr;
+		return vgic_v3_attr_regs_access(dev, attr, false);
-		u64 reg;
-		u32 tmp32;
-
-		ret = vgic_v3_attr_regs_access(dev, attr, &reg, false);
-		if (ret)
-			return ret;
-		tmp32 = reg;
-		return put_user(tmp32, uaddr);
-	}
 	case KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS:
-		return vgic_v3_attr_regs_access(dev, attr, NULL, false);
+		return vgic_v3_attr_regs_access(dev, attr, false);
-	case KVM_DEV_ARM_VGIC_GRP_LEVEL_INFO: {
+	case KVM_DEV_ARM_VGIC_GRP_LEVEL_INFO:
-		u32 __user *uaddr = (u32 __user *)(long)attr->addr;
+		return vgic_v3_attr_regs_access(dev, attr, false);
-		u64 reg;
-		u32 tmp32;
-
-		ret = vgic_v3_attr_regs_access(dev, attr, &reg, false);
-		if (ret)
-			return ret;
-		tmp32 = reg;
-		return put_user(tmp32, uaddr);
-	}
 	}
 	return -ENXIO;
 }