Re: [Intel-gfx] [PATCH v2] drm/i915: Fix vm use-after-free in vma destruction

[Andrzej Hajda]

On 20.06.2022 14:36, Thomas Hellström wrote:

In vma destruction, the following race may occur:

Thread 1:                         Thread 2:
i915_vma_destroy();

   ...
   list_del_init(vma->vm_link);
   ...
   mutex_unlock(vma->vm->mutex);
                                  __i915_vm_release();
release_references();

And in release_reference() we dereference vma->vm to get to the
vm gt pointer, leading to a use-after free.

However, __i915_vm_release() grabs the vm->mutex so the vm won't be
destroyed before vma->vm->mutex is released, so extract the gt pointer
under the vm->mutex to avoid the vma->vm dereference in
release_references().

v2: Fix a typo in the commit message (Andi Shyti)

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5944
Fixes: e1a7ab4fca ("drm/i915: Remove the vm open count")

Cc: Niranjana Vishwanathapura <niranjana.vishwanathap...@intel.com>
Cc: Matthew Auld <matthew.a...@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellst...@linux.intel.com>
---
  drivers/gpu/drm/i915/i915_vma.c | 12 ++++++++----
  1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 0bffb70b3c5f..04d12f278f57 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -1637,10 +1637,10 @@ static void force_unbind(struct i915_vma *vma)
        GEM_BUG_ON(drm_mm_node_allocated(&vma->node));
  }

-static void release_references(struct i915_vma *vma, bool vm_ddestroy)

+static void release_references(struct i915_vma *vma, struct intel_gt *gt,
+                              bool vm_ddestroy)
  {
        struct drm_i915_gem_object *obj = vma->obj;
-       struct intel_gt *gt = vma->vm->gt;

GEM_BUG_ON(i915_vma_is_active(vma)); @@ -1695,11 +1695,12 @@ void i915_vma_destroy_locked(struct i915_vma *vma) force_unbind(vma);

        list_del_init(&vma->vm_link);
-       release_references(vma, false);
+       release_references(vma, vma->vm->gt, false);
  }

void i915_vma_destroy(struct i915_vma *vma)

  {
+       struct intel_gt *gt;
        bool vm_ddestroy;

mutex_lock(&vma->vm->mutex);

@@ -1707,8 +1708,11 @@ void i915_vma_destroy(struct i915_vma *vma)
        list_del_init(&vma->vm_link);
        vm_ddestroy = vma->vm_ddestroy;
        vma->vm_ddestroy = false;
+
+       /* vma->vm may be freed when releasing vma->vm->mutex. */
+       gt = vma->vm->gt;
        mutex_unlock(&vma->vm->mutex);
-       release_references(vma, vm_ddestroy);
+       release_references(vma, gt, vm_ddestroy);

Reviewed-by: Andrzej Hajda <andrzej.ha...@intel.com>

Regards
Andrzej

  }

void i915_vma_parked(struct intel_gt *gt)