drm/xe/vm: prevent UAF in rebind_work_func()

We flush the rebind worker during the vm close phase, however in places
like preempt_fence_work_func() we seem to queue the rebind worker
without first checking if the vm has already been closed.  The concern
here is the vm being closed with the worker flushed, but then being
rearmed later, which looks like potential uaf, since there is no actual
refcounting to track the queued worker. We can't take the vm->lock here
in preempt_rebind_work_func() to first check if the vm is closed since
that will deadlock, so instead flush the worker again when the vm
refcount reaches zero.

v2:
 - Grabbing vm->lock in the preempt worker creates a deadlock, so
   checking the closed state is tricky. Instead flush the worker when
   the refcount reaches zero. It should be impossible to queue the
   preempt worker without already holding vm ref.

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1676
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1591
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1364
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1304
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/1249
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <stable@vger.kernel.org> # v6.8+
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240423074721.119633-4-matthew.auld@intel.com
(cherry picked from commit 3d44d67c441a9fe6f81a1d705f7de009a32a5b35)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index 7ae2b0300db65c2315b1bed2b15ee117ee61f59e..4aa3943e6f292263f1bc353009bfddd03c2ca689 100644 (file)
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -1499,6 +1499,9 @@ static void xe_vm_free(struct drm_gpuvm *gpuvm)
        /* xe_vm_close_and_put was not called? */
        xe_assert(xe, !vm->size);
 
+       if (xe_vm_in_preempt_fence_mode(vm))
+               flush_work(&vm->preempt.rebind_work);
+
        mutex_destroy(&vm->snap_mutex);
 
        if (!(vm->flags & XE_VM_FLAG_MIGRATION))