drm/panthor: Keep a ref to the VM at the panthor_kernel_bo level

Avoids use-after-free situations when panthor_fw_unplug() is called
and the kernel BO was mapped to the FW VM.
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240502183813.1612017-3-boris.brezillon@collabora.com

drivers/gpu/drm/panthor/panthor_fw.c

@@ -453,7 +453,7 @@ panthor_fw_alloc_queue_iface_mem(struct panthor_device *ptdev,
 
 	ret = panthor_kernel_bo_vmap(mem);
 	if (ret) {
-		panthor_kernel_bo_destroy(panthor_fw_vm(ptdev), mem);
+		panthor_kernel_bo_destroy(mem);
 		return ERR_PTR(ret);
 	}
 
@@ -1134,7 +1134,7 @@ void panthor_fw_unplug(struct panthor_device *ptdev)
 	panthor_fw_stop(ptdev);
 
 	list_for_each_entry(section, &ptdev->fw->sections, node)
-		panthor_kernel_bo_destroy(panthor_fw_vm(ptdev), section->mem);
+		panthor_kernel_bo_destroy(section->mem);
 
 	/* We intentionally don't call panthor_vm_idle() and let
 	 * panthor_mmu_unplug() release the AS we acquired with

drivers/gpu/drm/panthor/panthor_gem.c

@@ -26,18 +26,18 @@ static void panthor_gem_free_object(struct drm_gem_object *obj)
 
 /**
  * panthor_kernel_bo_destroy() - Destroy a kernel buffer object
- * @vm: The VM this BO was mapped to.
  * @bo: Kernel buffer object to destroy. If NULL or an ERR_PTR(), the destruction
  * is skipped.
  */
-void panthor_kernel_bo_destroy(struct panthor_vm *vm,
-			       struct panthor_kernel_bo *bo)
+void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo)
 {
+	struct panthor_vm *vm;
 	int ret;
 
 	if (IS_ERR_OR_NULL(bo))
 		return;
 
+	vm = bo->vm;
 	panthor_kernel_bo_vunmap(bo);
 
 	if (drm_WARN_ON(bo->obj->dev,
@@ -53,6 +53,7 @@ void panthor_kernel_bo_destroy(struct panthor_vm *vm,
 	drm_gem_object_put(bo->obj);
 
 out_free_bo:
+	panthor_vm_put(vm);
 	kfree(bo);
 }
 
@@ -106,6 +107,7 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
 	if (ret)
 		goto err_free_va;
 
+	kbo->vm = panthor_vm_get(vm);
 	bo->exclusive_vm_root_gem = panthor_vm_root_gem(vm);
 	drm_gem_object_get(bo->exclusive_vm_root_gem);
 	bo->base.base.resv = bo->exclusive_vm_root_gem->resv;

drivers/gpu/drm/panthor/panthor_gem.h

@@ -61,6 +61,11 @@ struct panthor_kernel_bo {
 	 */
 	struct drm_gem_object *obj;
 
+	/**
+	 * @vm: VM this private buffer is attached to.
+	 */
+	struct panthor_vm *vm;
+
 	/**
 	 * @va_node: VA space allocated to this GEM.
 	 */
@@ -136,7 +141,6 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
 			 size_t size, u32 bo_flags, u32 vm_map_flags,
 			 u64 gpu_va);
 
-void panthor_kernel_bo_destroy(struct panthor_vm *vm,
-			       struct panthor_kernel_bo *bo);
+void panthor_kernel_bo_destroy(struct panthor_kernel_bo *bo);
 
 #endif /* __PANTHOR_GEM_H__ */

drivers/gpu/drm/panthor/panthor_heap.c

@@ -127,7 +127,7 @@ static void panthor_free_heap_chunk(struct panthor_vm *vm,
 	heap->chunk_count--;
 	mutex_unlock(&heap->lock);
 
-	panthor_kernel_bo_destroy(vm, chunk->bo);
+	panthor_kernel_bo_destroy(chunk->bo);
 	kfree(chunk);
 }
 
@@ -183,7 +183,7 @@ static int panthor_alloc_heap_chunk(struct panthor_device *ptdev,
 	return 0;
 
 err_destroy_bo:
-	panthor_kernel_bo_destroy(vm, chunk->bo);
+	panthor_kernel_bo_destroy(chunk->bo);
 
 err_free_chunk:
 	kfree(chunk);
@@ -395,7 +395,7 @@ int panthor_heap_return_chunk(struct panthor_heap_pool *pool,
 	mutex_unlock(&heap->lock);
 
 	if (removed) {
-		panthor_kernel_bo_destroy(pool->vm, chunk->bo);
+		panthor_kernel_bo_destroy(chunk->bo);
 		kfree(chunk);
 		ret = 0;
 	} else {
@@ -595,7 +595,7 @@ void panthor_heap_pool_destroy(struct panthor_heap_pool *pool)
 		drm_WARN_ON(&pool->ptdev->base, panthor_heap_destroy_locked(pool, i));
 
 	if (!IS_ERR_OR_NULL(pool->gpu_contexts))
-		panthor_kernel_bo_destroy(pool->vm, pool->gpu_contexts);
+		panthor_kernel_bo_destroy(pool->gpu_contexts);
 
 	/* Reflects the fact the pool has been destroyed. */
 	pool->vm = NULL;

drivers/gpu/drm/panthor/panthor_sched.c

@@ -826,8 +826,8 @@ static void group_free_queue(struct panthor_group *group, struct panthor_queue *
 
 	panthor_queue_put_syncwait_obj(queue);
 
-	panthor_kernel_bo_destroy(group->vm, queue->ringbuf);
-	panthor_kernel_bo_destroy(panthor_fw_vm(group->ptdev), queue->iface.mem);
+	panthor_kernel_bo_destroy(queue->ringbuf);
+	panthor_kernel_bo_destroy(queue->iface.mem);
 
 	kfree(queue);
 }
@@ -837,15 +837,14 @@ static void group_release_work(struct work_struct *work)
 	struct panthor_group *group = container_of(work,
 						   struct panthor_group,
 						   release_work);
-	struct panthor_device *ptdev = group->ptdev;
 	u32 i;
 
 	for (i = 0; i < group->queue_count; i++)
 		group_free_queue(group, group->queues[i]);
 
-	panthor_kernel_bo_destroy(panthor_fw_vm(ptdev), group->suspend_buf);
-	panthor_kernel_bo_destroy(panthor_fw_vm(ptdev), group->protm_suspend_buf);
-	panthor_kernel_bo_destroy(group->vm, group->syncobjs);
+	panthor_kernel_bo_destroy(group->suspend_buf);
+	panthor_kernel_bo_destroy(group->protm_suspend_buf);
+	panthor_kernel_bo_destroy(group->syncobjs);
 
 	panthor_vm_put(group->vm);
 	kfree(group);