vfio/pci: Use the struct file as the handle not the vfio_group

VFIO PCI does a security check as part of hot reset to prove that the user
has permission to manipulate all the devices that will be impacted by the
reset.

Use a new API vfio_file_has_dev() to perform this security check against
the struct file directly and remove the vfio_group from VFIO PCI.

Since VFIO PCI was the last user of vfio_group_get_external_user() and
vfio_group_put_external_user() remove it as well.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/8-v3-f7729924a7ea+25e33-vfio_kvm_no_group_jgg@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci_core.c

@@ -556,7 +556,7 @@ static int vfio_pci_fill_devs(struct pci_dev *pdev, void *data)
 
 struct vfio_pci_group_info {
 	int count;
-	struct vfio_group **groups;
+	struct file **files;
 };
 
 static bool vfio_pci_dev_below_slot(struct pci_dev *pdev, struct pci_slot *slot)
@@ -1018,10 +1018,10 @@ long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
 	} else if (cmd == VFIO_DEVICE_PCI_HOT_RESET) {
 		struct vfio_pci_hot_reset hdr;
 		int32_t *group_fds;
-		struct vfio_group **groups;
+		struct file **files;
 		struct vfio_pci_group_info info;
 		bool slot = false;
-		int group_idx, count = 0, ret = 0;
+		int file_idx, count = 0, ret = 0;
 
 		minsz = offsetofend(struct vfio_pci_hot_reset, count);
 
@@ -1054,17 +1054,17 @@ long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
 			return -EINVAL;
 
 		group_fds = kcalloc(hdr.count, sizeof(*group_fds), GFP_KERNEL);
-		groups = kcalloc(hdr.count, sizeof(*groups), GFP_KERNEL);
-		if (!group_fds || !groups) {
+		files = kcalloc(hdr.count, sizeof(*files), GFP_KERNEL);
+		if (!group_fds || !files) {
 			kfree(group_fds);
-			kfree(groups);
+			kfree(files);
 			return -ENOMEM;
 		}
 
 		if (copy_from_user(group_fds, (void __user *)(arg + minsz),
 				   hdr.count * sizeof(*group_fds))) {
 			kfree(group_fds);
-			kfree(groups);
+			kfree(files);
 			return -EFAULT;
 		}
 
@@ -1073,22 +1073,22 @@ long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
 		 * user interface and store the group and iommu ID.  This
 		 * ensures the group is held across the reset.
 		 */
-		for (group_idx = 0; group_idx < hdr.count; group_idx++) {
-			struct vfio_group *group;
-			struct fd f = fdget(group_fds[group_idx]);
-			if (!f.file) {
+		for (file_idx = 0; file_idx < hdr.count; file_idx++) {
+			struct file *file = fget(group_fds[file_idx]);
+
+			if (!file) {
 				ret = -EBADF;
 				break;
 			}
 
-			group = vfio_group_get_external_user(f.file);
-			fdput(f);
-			if (IS_ERR(group)) {
-				ret = PTR_ERR(group);
+			/* Ensure the FD is a vfio group FD.*/
+			if (!vfio_file_iommu_group(file)) {
+				fput(file);
+				ret = -EINVAL;
 				break;
 			}
 
-			groups[group_idx] = group;
+			files[file_idx] = file;
 		}
 
 		kfree(group_fds);
@@ -1098,15 +1098,15 @@ long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
 			goto hot_reset_release;
 
 		info.count = hdr.count;
-		info.groups = groups;
+		info.files = files;
 
 		ret = vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, &info);
 
 hot_reset_release:
-		for (group_idx--; group_idx >= 0; group_idx--)
-			vfio_group_put_external_user(groups[group_idx]);
+		for (file_idx--; file_idx >= 0; file_idx--)
+			fput(files[file_idx]);
 
-		kfree(groups);
+		kfree(files);
 		return ret;
 	} else if (cmd == VFIO_DEVICE_IOEVENTFD) {
 		struct vfio_device_ioeventfd ioeventfd;
@@ -1972,7 +1972,7 @@ static bool vfio_dev_in_groups(struct vfio_pci_core_device *vdev,
 	unsigned int i;
 
 	for (i = 0; i < groups->count; i++)
-		if (groups->groups[i] == vdev->vdev.group)
+		if (vfio_file_has_dev(groups->files[i], &vdev->vdev))
 			return true;
 	return false;
 }

drivers/vfio/vfio.c

@@ -1633,58 +1633,6 @@ static const struct file_operations vfio_device_fops = {
 	.mmap		= vfio_device_fops_mmap,
 };
 
-/*
- * External user API, exported by symbols to be linked dynamically.
- *
- * The protocol includes:
- *  1. do normal VFIO init operation:
- *	- opening a new container;
- *	- attaching group(s) to it;
- *	- setting an IOMMU driver for a container.
- * When IOMMU is set for a container, all groups in it are
- * considered ready to use by an external user.
- *
- * 2. User space passes a group fd to an external user.
- * The external user calls vfio_group_get_external_user()
- * to verify that:
- *	- the group is initialized;
- *	- IOMMU is set for it.
- * If both checks passed, vfio_group_get_external_user()
- * increments the container user counter to prevent
- * the VFIO group from disposal before KVM exits.
- *
- * 3. When the external KVM finishes, it calls
- * vfio_group_put_external_user() to release the VFIO group.
- * This call decrements the container user counter.
- */
-struct vfio_group *vfio_group_get_external_user(struct file *filep)
-{
-	struct vfio_group *group = filep->private_data;
-	int ret;
-
-	if (filep->f_op != &vfio_group_fops)
-		return ERR_PTR(-EINVAL);
-
-	ret = vfio_group_add_container_user(group);
-	if (ret)
-		return ERR_PTR(ret);
-
-	/*
-	 * Since the caller holds the fget on the file group->users must be >= 1
-	 */
-	vfio_group_get(group);
-
-	return group;
-}
-EXPORT_SYMBOL_GPL(vfio_group_get_external_user);
-
-void vfio_group_put_external_user(struct vfio_group *group)
-{
-	vfio_group_try_dissolve_container(group);
-	vfio_group_put(group);
-}
-EXPORT_SYMBOL_GPL(vfio_group_put_external_user);
-
 /**
  * vfio_file_iommu_group - Return the struct iommu_group for the vfio group file
  * @file: VFIO group file
@@ -1752,6 +1700,24 @@ void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
 }
 EXPORT_SYMBOL_GPL(vfio_file_set_kvm);
 
+/**
+ * vfio_file_has_dev - True if the VFIO file is a handle for device
+ * @file: VFIO file to check
+ * @device: Device that must be part of the file
+ *
+ * Returns true if given file has permission to manipulate the given device.
+ */
+bool vfio_file_has_dev(struct file *file, struct vfio_device *device)
+{
+	struct vfio_group *group = file->private_data;
+
+	if (file->f_op != &vfio_group_fops)
+		return false;
+
+	return group == device->group;
+}
+EXPORT_SYMBOL_GPL(vfio_file_has_dev);
+
 /*
  * Sub-module support
  */

include/linux/vfio.h

@@ -138,11 +138,10 @@ int vfio_mig_get_next_state(struct vfio_device *device,
 /*
  * External user API
  */
-extern struct vfio_group *vfio_group_get_external_user(struct file *filep);
-extern void vfio_group_put_external_user(struct vfio_group *group);
 extern struct iommu_group *vfio_file_iommu_group(struct file *file);
 extern bool vfio_file_enforced_coherent(struct file *file);
 extern void vfio_file_set_kvm(struct file *file, struct kvm *kvm);
+extern bool vfio_file_has_dev(struct file *file, struct vfio_device *device);
 
 #define VFIO_PIN_PAGES_MAX_ENTRIES	(PAGE_SIZE/sizeof(unsigned long))