drm/amdgpu: Fix one use-after-free of VM

VM might already be freed when amdgpu_vm_tlb_seq_cb() is called.
We see the calltrace below.

Fix it by keeping the last flush fence around and wait for it to signal

BUG kmalloc-4k (Not tainted): Poison overwritten

0xffff9c88630414e8-0xffff9c88630414e8 @offset=5352. First byte 0x6c
instead of 0x6b Allocated in amdgpu_driver_open_kms+0x9d/0x360 [amdgpu]
age=44 cpu=0 pid=2343
 __slab_alloc.isra.0+0x4f/0x90
 kmem_cache_alloc_trace+0x6b8/0x7a0
 amdgpu_driver_open_kms+0x9d/0x360 [amdgpu]
 drm_file_alloc+0x222/0x3e0 [drm]
 drm_open+0x11d/0x410 [drm]
Freed in amdgpu_driver_postclose_kms+0x3e9/0x550 [amdgpu] age=22 cpu=1
pid=2485
 kfree+0x4a2/0x580
 amdgpu_driver_postclose_kms+0x3e9/0x550 [amdgpu]
 drm_file_free+0x24e/0x3c0 [drm]
 drm_close_helper.isra.0+0x90/0xb0 [drm]
 drm_release+0x97/0x1a0 [drm]
 __fput+0xb6/0x280
 ____fput+0xe/0x10
 task_work_run+0x64/0xb0

Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c

@@ -932,10 +932,14 @@ int amdgpu_vm_update_range(struct amdgpu_device *adev, struct amdgpu_vm *vm,
 
 	if (flush_tlb || params.table_freed) {
 		tlb_cb->vm = vm;
-		if (!fence || !*fence ||
-		    dma_fence_add_callback(*fence, &tlb_cb->cb,
-					   amdgpu_vm_tlb_seq_cb))
+		if (fence && *fence &&
+		    !dma_fence_add_callback(*fence, &tlb_cb->cb,
+					   amdgpu_vm_tlb_seq_cb)) {
+			dma_fence_put(vm->last_tlb_flush);
+			vm->last_tlb_flush = dma_fence_get(*fence);
+		} else {
 			amdgpu_vm_tlb_seq_cb(NULL, &tlb_cb->cb);
+		}
 		tlb_cb = NULL;
 	}
 
@@ -2094,6 +2098,7 @@ int amdgpu_vm_init(struct amdgpu_device *adev, struct amdgpu_vm *vm)
 		vm->update_funcs = &amdgpu_vm_sdma_funcs;
 	vm->last_update = NULL;
 	vm->last_unlocked = dma_fence_get_stub();
+	vm->last_tlb_flush = dma_fence_get_stub();
 
 	mutex_init(&vm->eviction_lock);
 	vm->evicting = false;
@@ -2132,6 +2137,7 @@ int amdgpu_vm_init(struct amdgpu_device *adev, struct amdgpu_vm *vm)
 	vm->root.bo = NULL;
 
 error_free_delayed:
+	dma_fence_put(vm->last_tlb_flush);
 	dma_fence_put(vm->last_unlocked);
 	drm_sched_entity_destroy(&vm->delayed);
 
@@ -2248,6 +2254,7 @@ void amdgpu_vm_fini(struct amdgpu_device *adev, struct amdgpu_vm *vm)
 	struct amdgpu_bo_va_mapping *mapping, *tmp;
 	bool prt_fini_needed = !!adev->gmc.gmc_funcs->set_prt;
 	struct amdgpu_bo *root;
+	unsigned long flags;
 	int i;
 
 	amdgpu_amdkfd_gpuvm_destroy_cb(adev, vm);
@@ -2257,6 +2264,11 @@ void amdgpu_vm_fini(struct amdgpu_device *adev, struct amdgpu_vm *vm)
 	amdgpu_vm_set_pasid(adev, vm, 0);
 	dma_fence_wait(vm->last_unlocked, false);
 	dma_fence_put(vm->last_unlocked);
+	dma_fence_wait(vm->last_tlb_flush, false);
+	/* Make sure that all fence callbacks have completed */
+	spin_lock_irqsave(vm->last_tlb_flush->lock, flags);
+	spin_unlock_irqrestore(vm->last_tlb_flush->lock, flags);
+	dma_fence_put(vm->last_tlb_flush);
 
 	list_for_each_entry_safe(mapping, tmp, &vm->freed, list) {
 		if (mapping->flags & AMDGPU_PTE_PRT && prt_fini_needed) {

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h

@@ -286,6 +286,7 @@ struct amdgpu_vm {
 
 	/* Last finished delayed update */
 	atomic64_t		tlb_seq;
+	struct dma_fence	*last_tlb_flush;
 
 	/* Last unlocked submission to the scheduler entities */
 	struct dma_fence	*last_unlocked;