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.vishwanathapura@xxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
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.hajda@xxxxxxxxx>
Regards
Andrzej
}
void i915_vma_parked(struct intel_gt *gt)
