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vfio: Add missing locking for struct vfio_group::kvm

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Without locking userspace can trigger a UAF by racing
KVM_DEV_VFIO_GROUP_DEL with VFIO_GROUP_GET_DEVICE_FD:

              CPU1                               CPU2
					    ioctl(KVM_DEV_VFIO_GROUP_DEL)
 ioctl(VFIO_GROUP_GET_DEVICE_FD)
    vfio_group_get_device_fd
     open_device()
      intel_vgpu_open_device()
        vfio_register_notifier()
	 vfio_register_group_notifier()
	   blocking_notifier_call_chain(&group->notifier,
               VFIO_GROUP_NOTIFY_SET_KVM, group->kvm);

					      set_kvm()
						group->kvm = NULL
					    close()
					     kfree(kvm)

             intel_vgpu_group_notifier()
                vdev->kvm = data
    [..]
        kvm_get_kvm(vgpu->kvm);
	    // UAF!

Add a simple rwsem in the group to protect the kvm while the notifier is
using it.

Note this doesn't fix the race internal to i915 where userspace can
trigger two VFIO_GROUP_NOTIFY_SET_KVM's before we reach a consumer of
vgpu->kvm and trigger this same UAF, it just makes the notifier
self-consistent.

Fixes: ccd46dbae7 ("vfio: support notifier chain in vfio_group")
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/1-v2-d035a1842d81+1bf-vfio_group_locking_jgg@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
This commit is contained in:
Jason Gunthorpe 2022-05-16 20:41:17 -03:00 committed by Alex Williamson
parent 6b17ca8e5e
commit be8d3adae6
1 changed files with 15 additions and 4 deletions
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19
drivers/vfio/vfio.c
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@ -76,6 +76,7 @@ struct vfio_group {
atomic_t opened;
enum vfio_group_type type;
unsigned int dev_counter;
struct rw_semaphore group_rwsem;
struct kvm *kvm;
struct blocking_notifier_head notifier;
};
@ -360,6 +361,7 @@ static struct vfio_group *vfio_group_alloc(struct iommu_group *iommu_group,
group->cdev.owner = THIS_MODULE;
refcount_set(&group->users, 1);
init_rwsem(&group->group_rwsem);
INIT_LIST_HEAD(&group->device_list);
mutex_init(&group->device_lock);
group->iommu_group = iommu_group;
@ -1694,9 +1696,11 @@ void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
if (file->f_op != &vfio_group_fops)
return;
down_write(&group->group_rwsem);
group->kvm = kvm;
blocking_notifier_call_chain(&group->notifier,
VFIO_GROUP_NOTIFY_SET_KVM, kvm);
up_write(&group->group_rwsem);
}
EXPORT_SYMBOL_GPL(vfio_file_set_kvm);
@ -2004,15 +2008,22 @@ static int vfio_register_group_notifier(struct vfio_group *group,
return -EINVAL;
ret = blocking_notifier_chain_register(&group->notifier, nb);
if (ret)
return ret;
/*
* The attaching of kvm and vfio_group might already happen, so
* here we replay once upon registration.
*/
if (!ret && set_kvm && group->kvm)
blocking_notifier_call_chain(&group->notifier,
VFIO_GROUP_NOTIFY_SET_KVM, group->kvm);
return ret;
if (set_kvm) {
down_read(&group->group_rwsem);
if (group->kvm)
blocking_notifier_call_chain(&group->notifier,
VFIO_GROUP_NOTIFY_SET_KVM,
group->kvm);
up_read(&group->group_rwsem);
}
return 0;
}
int vfio_register_notifier(struct vfio_device *device,