vfio: Fully lock struct vfio_group::container

This is necessary to avoid various user triggerable races, for instance
racing SET_CONTAINER/UNSET_CONTAINER:

                                  ioctl(VFIO_GROUP_SET_CONTAINER)
ioctl(VFIO_GROUP_UNSET_CONTAINER)
 vfio_group_unset_container
    int users = atomic_cmpxchg(&group->container_users, 1, 0);
    // users == 1 container_users == 0
    __vfio_group_unset_container(group);
      container = group->container;
                                    vfio_group_set_container()
	                              if (!atomic_read(&group->container_users))
				        down_write(&container->group_lock);
				        group->container = container;
				        up_write(&container->group_lock);

      down_write(&container->group_lock);
      group->container = NULL;
      up_write(&container->group_lock);
      vfio_container_put(container);
      /* woops we lost/leaked the new container  */

This can then go on to NULL pointer deref since container == 0 and
container_users == 1.

Wrap all touches of container, except those on a performance path with a
known open device, with the group_rwsem.

The only user of vfio_group_add_container_user() holds the user count for
a simple operation, change it to just hold the group_lock over the
operation and delete vfio_group_add_container_user(). Containers now only
gain a user when a device FD is opened.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/r/4-v2-d035a1842d81+1bf-vfio_group_locking_jgg@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 21db0e8..81330c8 100644 (file)
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -918,6 +918,8 @@ static void __vfio_group_unset_container(struct vfio_group *group)
        struct vfio_container *container = group->container;
        struct vfio_iommu_driver *driver;
 
+       lockdep_assert_held_write(&group->group_rwsem);
+
        down_write(&container->group_lock);
 
        driver = container->iommu_driver;
@@ -953,6 +955,8 @@ static int vfio_group_unset_container(struct vfio_group *group)
 {
        int users = atomic_cmpxchg(&group->container_users, 1, 0);
 
+       lockdep_assert_held_write(&group->group_rwsem);
+
        if (!users)
                return -EINVAL;
        if (users != 1)
@@ -971,8 +975,10 @@ static int vfio_group_unset_container(struct vfio_group *group)
  */
 static void vfio_group_try_dissolve_container(struct vfio_group *group)
 {
+       down_write(&group->group_rwsem);
        if (0 == atomic_dec_if_positive(&group->container_users))
                __vfio_group_unset_container(group);
+       up_write(&group->group_rwsem);
 }
 
 static int vfio_group_set_container(struct vfio_group *group, int container_fd)
@@ -982,6 +988,8 @@ static int vfio_group_set_container(struct vfio_group *group, int container_fd)
        struct vfio_iommu_driver *driver;
        int ret = 0;
 
+       lockdep_assert_held_write(&group->group_rwsem);
+
        if (atomic_read(&group->container_users))
                return -EINVAL;
 
@@ -1039,23 +1047,6 @@ unlock_out:
        return ret;
 }
 
-static int vfio_group_add_container_user(struct vfio_group *group)
-{
-       if (!atomic_inc_not_zero(&group->container_users))
-               return -EINVAL;
-
-       if (group->type == VFIO_NO_IOMMU) {
-               atomic_dec(&group->container_users);
-               return -EPERM;
-       }
-       if (!group->container->iommu_driver) {
-               atomic_dec(&group->container_users);
-               return -EINVAL;
-       }
-
-       return 0;
-}
-
 static const struct file_operations vfio_device_fops;
 
 /* true if the vfio_device has open_device() called but not close_device() */
@@ -1068,6 +1059,8 @@ static int vfio_device_assign_container(struct vfio_device *device)
 {
        struct vfio_group *group = device->group;
 
+       lockdep_assert_held_write(&group->group_rwsem);
+
        if (0 == atomic_read(&group->container_users) ||
            !group->container->iommu_driver)
                return -EINVAL;
@@ -1084,7 +1077,9 @@ static struct file *vfio_device_open(struct vfio_device *device)
        struct file *filep;
        int ret;
 
+       down_write(&device->group->group_rwsem);
        ret = vfio_device_assign_container(device);
+       up_write(&device->group->group_rwsem);
        if (ret)
                return ERR_PTR(ret);
 
@@ -1197,11 +1192,13 @@ static long vfio_group_fops_unl_ioctl(struct file *filep,
 
                status.flags = 0;
 
+               down_read(&group->group_rwsem);
                if (group->container)
                        status.flags |= VFIO_GROUP_FLAGS_CONTAINER_SET |
                                        VFIO_GROUP_FLAGS_VIABLE;
                else if (!iommu_group_dma_owner_claimed(group->iommu_group))
                        status.flags |= VFIO_GROUP_FLAGS_VIABLE;
+               up_read(&group->group_rwsem);
 
                if (copy_to_user((void __user *)arg, &status, minsz))
                        return -EFAULT;
@@ -1219,11 +1216,15 @@ static long vfio_group_fops_unl_ioctl(struct file *filep,
                if (fd < 0)
                        return -EINVAL;
 
+               down_write(&group->group_rwsem);
                ret = vfio_group_set_container(group, fd);
+               up_write(&group->group_rwsem);
                break;
        }
        case VFIO_GROUP_UNSET_CONTAINER:
+               down_write(&group->group_rwsem);
                ret = vfio_group_unset_container(group);
+               up_write(&group->group_rwsem);
                break;
        case VFIO_GROUP_GET_DEVICE_FD:
        {
@@ -1709,15 +1710,19 @@ bool vfio_file_enforced_coherent(struct file *file)
        if (file->f_op != &vfio_group_fops)
                return true;
 
-       /*
-        * Since the coherency state is determined only once a container is
-        * attached the user must do so before they can prove they have
-        * permission.
-        */
-       if (vfio_group_add_container_user(group))
-               return true;
-       ret = vfio_ioctl_check_extension(group->container, VFIO_DMA_CC_IOMMU);
-       vfio_group_try_dissolve_container(group);
+       down_read(&group->group_rwsem);
+       if (group->container) {
+               ret = vfio_ioctl_check_extension(group->container,
+                                                VFIO_DMA_CC_IOMMU);
+       } else {
+               /*
+                * Since the coherency state is determined only once a container
+                * is attached the user must do so before they can prove they
+                * have permission.
+                */
+               ret = true;
+       }
+       up_read(&group->group_rwsem);
        return ret;
 }
 EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
@@ -1910,6 +1915,7 @@ int vfio_pin_pages(struct vfio_device *device, unsigned long *user_pfn,
        if (group->dev_counter > 1)
                return -EINVAL;
 
+       /* group->container cannot change while a vfio device is open */
        container = group->container;
        driver = container->iommu_driver;
        if (likely(driver && driver->ops->pin_pages))
@@ -1945,6 +1951,7 @@ int vfio_unpin_pages(struct vfio_device *device, unsigned long *user_pfn,
        if (npage > VFIO_PIN_PAGES_MAX_ENTRIES)
                return -E2BIG;
 
+       /* group->container cannot change while a vfio device is open */
        container = device->group->container;
        driver = container->iommu_driver;
        if (likely(driver && driver->ops->unpin_pages))
@@ -1984,6 +1991,7 @@ int vfio_dma_rw(struct vfio_device *device, dma_addr_t user_iova, void *data,
        if (!data || len <= 0 || !vfio_assert_device_open(device))
                return -EINVAL;
 
+       /* group->container cannot change while a vfio device is open */
        container = device->group->container;
        driver = container->iommu_driver;
 
@@ -2004,6 +2012,7 @@ static int vfio_register_iommu_notifier(struct vfio_group *group,
        struct vfio_iommu_driver *driver;
        int ret;
 
+       down_read(&group->group_rwsem);
        container = group->container;
        driver = container->iommu_driver;
        if (likely(driver && driver->ops->register_notifier))
@@ -2011,6 +2020,8 @@ static int vfio_register_iommu_notifier(struct vfio_group *group,
                                                     events, nb);
        else
                ret = -ENOTTY;
+       up_read(&group->group_rwsem);
+
        return ret;
 }
 
@@ -2021,6 +2032,7 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group,
        struct vfio_iommu_driver *driver;
        int ret;
 
+       down_read(&group->group_rwsem);
        container = group->container;
        driver = container->iommu_driver;
        if (likely(driver && driver->ops->unregister_notifier))
@@ -2028,6 +2040,8 @@ static int vfio_unregister_iommu_notifier(struct vfio_group *group,
                                                       nb);
        else
                ret = -ENOTTY;
+       up_read(&group->group_rwsem);
+
        return ret;
 }