[PATCH v2] drm/amdgpu: Fix one use-after-free of VM

[Paul Menzel]

Dear Xinhui,


Thank you for rerolling the patch.

Am 14.04.22 um 07:03 schrieb xinhui pan:
> 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

Nit: Please add a dot/period to the end of sentences.

> 
> 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

The v2 annotation is missing.

> Suggested-by: Christian König <christian.koenig at amd.com>
> Signed-off-by: xinhui pan <xinhui.pan at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 17 ++++++++++++++---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h |  1 +
>   2 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> index 645ce28277c2..cd5aa7edd451 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> @@ -932,9 +932,12 @@ 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);

The Linux kernel coding style uses braces for all branches of a 
conditional statement, if one branch uses braces. [1]


Kind regards,

Paul


>   		tlb_cb = NULL;
>   	}
> @@ -2094,6 +2097,7 @@ 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 +2136,7 @@ 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 +2253,7 @@ 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 +2263,11 @@ 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) {
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> index 1a814fbffff8..6b06a214f05f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
> +++ b/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;


[1]: 
https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-braces-and-spaces