drm/msm: Fix use-after-free in msm_gem with carveout

When using gem with vram carveout the page allocation is managed via
drm_mm. The necessary drm_mm_node is allocated in add_vma, but it is
referenced in msm_gem_object as well. It is freed before the drm_mm_node
has been deallocated leading to use-after-free on every single vram
allocation.

Currently put_iova is called before put_pages in both
msm_gem_free_object and msm_gem_purge:

	put_iova -> del_vma -> kfree(vma) // vma holds drm_mm_node
	/* later */
	put_pages -> put_pages_vram -> drm_mm_remove_node(
						msm_obj->vram_node)
				 	// vram_node is a ref to
					// drm_mm_node; in _msm_gem_new

It looks like del_vma does nothing else other than freeing the vma
object and removing it from it's list, so delaying the deletion should
be harmless.

This patch splits put_iova in put_iova_spaces and put_iova_vmas, so the
vma can be freed after the mm_node has been deallocated with the mm.

Note: The breaking commit separated the vma allocation from within
msm_gem_object to outside, so the vram_node reference became outside the
msm_gem_object allocation, and freeing order was therefore overlooked.

Fixes: 4b85f7f ("drm/msm: support for an arbitrary number of address spaces")
Signed-off-by: Iskren Chernev <iskren.chernev@gmail.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>

Author: ichernev

drivers/gpu/drm/msm/msm_gem.c

@@ -358,18 +358,31 @@ static void del_vma(struct msm_gem_vma *vma)
 
 /* Called with msm_obj locked */
 static void
-put_iova(struct drm_gem_object *obj)
+put_iova_spaces(struct drm_gem_object *obj)
 {
 	struct msm_gem_object *msm_obj = to_msm_bo(obj);
-	struct msm_gem_vma *vma, *tmp;
+	struct msm_gem_vma *vma;
 
 	WARN_ON(!msm_gem_is_locked(obj));
 
-	list_for_each_entry_safe(vma, tmp, &msm_obj->vmas, list) {
+	list_for_each_entry(vma, &msm_obj->vmas, list) {
 		if (vma->aspace) {
 			msm_gem_purge_vma(vma->aspace, vma);
 			msm_gem_close_vma(vma->aspace, vma);
 		}
+	}
+}
+
+/* Called with msm_obj locked */
+static void
+put_iova_vmas(struct drm_gem_object *obj)
+{
+	struct msm_gem_object *msm_obj = to_msm_bo(obj);
+	struct msm_gem_vma *vma, *tmp;
+
+	WARN_ON(!msm_gem_is_locked(obj));
+
+	list_for_each_entry_safe(vma, tmp, &msm_obj->vmas, list) {
 		del_vma(vma);
 	}
 }
@@ -697,12 +710,14 @@ void msm_gem_purge(struct drm_gem_object *obj)
 	WARN_ON(!is_purgeable(msm_obj));
 	WARN_ON(obj->import_attach);
 
-	put_iova(obj);
+	put_iova_spaces(obj);
 
 	msm_gem_vunmap(obj);
 
 	put_pages(obj);
 
+	put_iova_vmas(obj);
+
 	msm_obj->madv = __MSM_MADV_PURGED;
 
 	drm_vma_node_unmap(&obj->vma_node, dev->anon_inode->i_mapping);
@@ -964,7 +979,7 @@ void msm_gem_free_object(struct drm_gem_object *obj)
 	/* object should not be on active list: */
 	WARN_ON(is_active(msm_obj));
 
-	put_iova(obj);
+	put_iova_spaces(obj);
 
 	if (obj->import_attach) {
 		WARN_ON(msm_obj->vaddr);
@@ -987,6 +1002,8 @@ void msm_gem_free_object(struct drm_gem_object *obj)
 		msm_gem_unlock(obj);
 	}
 
+	put_iova_vmas(obj);
+
 	drm_gem_object_release(obj);
 
 	kfree(msm_obj);