KVM: Remove ability to assign a device without iommu support

This option has no users and it exposes a security hole that we
can allow devices to be assigned without iommu protection.  Make
KVM_DEV_ASSIGN_ENABLE_IOMMU a mandatory option.
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Documentation/virtual/kvm/api.txt

@@ -1151,6 +1151,9 @@ following flags are specified:
 /* Depends on KVM_CAP_IOMMU */
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
 
+The KVM_DEV_ASSIGN_ENABLE_IOMMU flag is a mandatory option to ensure
+isolation of the device.  Usages not specifying this flag are deprecated.
+
 4.49 KVM_DEASSIGN_PCI_DEVICE
 
 Capability: KVM_CAP_DEVICE_DEASSIGNMENT

virt/kvm/assigned-dev.c

@@ -487,6 +487,9 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
 	struct kvm_assigned_dev_kernel *match;
 	struct pci_dev *dev;
 
+	if (!(assigned_dev->flags & KVM_DEV_ASSIGN_ENABLE_IOMMU))
+		return -EINVAL;
+
 	mutex_lock(&kvm->lock);
 	idx = srcu_read_lock(&kvm->srcu);
 
@@ -544,7 +547,6 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
 
 	list_add(&match->list, &kvm->arch.assigned_dev_head);
 
-	if (assigned_dev->flags & KVM_DEV_ASSIGN_ENABLE_IOMMU) {
 	if (!kvm->arch.iommu_domain) {
 		r = kvm_iommu_map_guest(kvm);
 		if (r)
@@ -553,7 +555,6 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
 	r = kvm_assign_device(kvm, match);
 	if (r)
 		goto out_list_del;
-	}
 
 out:
 	srcu_read_unlock(&kvm->srcu, idx);
@@ -593,7 +594,6 @@ static int kvm_vm_ioctl_deassign_device(struct kvm *kvm,
 		goto out;
 	}
 
-	if (match->flags & KVM_DEV_ASSIGN_ENABLE_IOMMU)
 	kvm_deassign_device(kvm, match);
 
 	kvm_free_assigned_device(kvm, match);