Re: [PATCH] drm/ttm: add a WARN_ON in ttm_set_driver_manager when array bounds (v2)

[Robin Murphy <robin.murphy@arm.com>]

On 2021-09-10 11:09, Guchun Chen wrote:
> Vendor will define their own memory types on top of TTM_PL_PRIV,
> but call ttm_set_driver_manager directly without checking mem_type
> value when setting up memory manager. So add such check to aware
> the case when array bounds.
> 
> v2: lower check level to WARN_ON
> 
> Signed-off-by: Leslie Shi <Yuliang.Shi@amd.com>
> Signed-off-by: Guchun Chen <guchun.chen@amd.com>
> ---
>   include/drm/ttm/ttm_device.h | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/include/drm/ttm/ttm_device.h b/include/drm/ttm/ttm_device.h
> index 07d722950d5b..aa79953c807c 100644
> --- a/include/drm/ttm/ttm_device.h
> +++ b/include/drm/ttm/ttm_device.h
> @@ -291,6 +291,7 @@ ttm_manager_type(struct ttm_device *bdev, int mem_type)
>   static inline void ttm_set_driver_manager(struct ttm_device *bdev, int type,
>   					  struct ttm_resource_manager *manager)
>   {
> +	WARN_ON(type >= TTM_NUM_MEM_TYPES);

Nit: I know nothing about this code, but from the context alone it would 
seem sensible to do

	if (WARN_ON(type >= TTM_NUM_MEM_TYPES))
		return;

to avoid making the subsequent assignment when we *know* it's invalid 
and likely to corrupt memory.

Robin.

>   	bdev->man_drv[type] = manager;
>   }
>   
>