Re: [PATCH v5] drm/mediatek: Fix coverity issue with unintentional integer overflow

[CK Hu (胡俊光)]

Hi, Jason:

On Thu, 2023-09-07 at 17:14 +0800, Jason-JH.Lin wrote:
> 1. Instead of multiplying 2 variable of different types. Change to
> assign a value of one variable and then multiply the other variable.
> 
> 2. Add a int variable for multiplier calculation instead of
> calculating
> different types multiplier with dma_addr_t variable directly.

Applied. Thanks.

Regards,
CK

> 
> Fixes: 1a64a7aff8da ("drm/mediatek: Fix cursor plane no update")
> Signed-off-by: Jason-JH.Lin <jason-jh.lin@xxxxxxxxxxxx>
> Reviewed-by: Alexandre Mergnat <amergnat@xxxxxxxxxxxx>
> Reviewed-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@xxxxxxxxxxxxx>
> ---
> Change in v5:
> Add 'coverity issue' in title and code comments.
> ---
>  drivers/gpu/drm/mediatek/mtk_drm_gem.c   |  9 +++++-
>  drivers/gpu/drm/mediatek/mtk_drm_plane.c | 39 ++++++++++++++++++--
> ----
>  2 files changed, 38 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> index 9f364df52478..f6632a0fe509 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> @@ -121,7 +121,14 @@ int mtk_drm_gem_dumb_create(struct drm_file
> *file_priv, struct drm_device *dev,
>  	int ret;
>  
>  	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
> -	args->size = args->pitch * args->height;
> +
> +	/*
> +	 * Multiply 2 variables of different types,
> +	 * for example: args->size = args->spacing * args->height;
> +	 * may cause coverity issue with unintentional overflow.
> +	 */
> +	args->size = args->pitch;
> +	args->size *= args->height;
>  
>  	mtk_gem = mtk_drm_gem_create(dev, args->size, false);
>  	if (IS_ERR(mtk_gem))
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> index db2f70ae060d..5acb03b7c6fe 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> @@ -141,6 +141,7 @@ static void mtk_plane_update_new_state(struct
> drm_plane_state *new_state,
>  	dma_addr_t addr;
>  	dma_addr_t hdr_addr = 0;
>  	unsigned int hdr_pitch = 0;
> +	int offset;
>  
>  	gem = fb->obj[0];
>  	mtk_gem = to_mtk_gem_obj(gem);
> @@ -150,8 +151,15 @@ static void mtk_plane_update_new_state(struct
> drm_plane_state *new_state,
>  	modifier = fb->modifier;
>  
>  	if (modifier == DRM_FORMAT_MOD_LINEAR) {
> -		addr += (new_state->src.x1 >> 16) * fb->format->cpp[0];
> -		addr += (new_state->src.y1 >> 16) * pitch;
> +		/*
> +		 * Using dma_addr_t variable to calculate with
> multiplier of different types,
> +		 * for example: addr += (new_state->src.x1 >> 16) * fb-
> >format->cpp[0];
> +		 * may cause coverity issue with unintentional
> overflow.
> +		 */
> +		offset = (new_state->src.x1 >> 16) * fb->format-
> >cpp[0];
> +		addr += offset;
> +		offset = (new_state->src.y1 >> 16) * pitch;
> +		addr += offset;
>  	} else {
>  		int width_in_blocks = ALIGN(fb->width,
> AFBC_DATA_BLOCK_WIDTH)
>  				      / AFBC_DATA_BLOCK_WIDTH;
> @@ -159,21 +167,34 @@ static void mtk_plane_update_new_state(struct
> drm_plane_state *new_state,
>  				       / AFBC_DATA_BLOCK_HEIGHT;
>  		int x_offset_in_blocks = (new_state->src.x1 >> 16) /
> AFBC_DATA_BLOCK_WIDTH;
>  		int y_offset_in_blocks = (new_state->src.y1 >> 16) /
> AFBC_DATA_BLOCK_HEIGHT;
> -		int hdr_size;
> +		int hdr_size, hdr_offset;
>  
>  		hdr_pitch = width_in_blocks * AFBC_HEADER_BLOCK_SIZE;
>  		pitch = width_in_blocks * AFBC_DATA_BLOCK_WIDTH *
>  			AFBC_DATA_BLOCK_HEIGHT * fb->format->cpp[0];
>  
>  		hdr_size = ALIGN(hdr_pitch * height_in_blocks,
> AFBC_HEADER_ALIGNMENT);
> +		hdr_offset = hdr_pitch * y_offset_in_blocks +
> +			AFBC_HEADER_BLOCK_SIZE * x_offset_in_blocks;
> +
> +		/*
> +		 * Using dma_addr_t variable to calculate with
> multiplier of different types,
> +		 * for example: addr += hdr_pitch * y_offset_in_blocks;
> +		 * may cause coverity issue with unintentional
> overflow.
> +		 */
> +		hdr_addr = addr + hdr_offset;
>  
> -		hdr_addr = addr + hdr_pitch * y_offset_in_blocks +
> -			   AFBC_HEADER_BLOCK_SIZE * x_offset_in_blocks;
>  		/* The data plane is offset by 1 additional block. */
> -		addr = addr + hdr_size +
> -		       pitch * y_offset_in_blocks +
> -		       AFBC_DATA_BLOCK_WIDTH * AFBC_DATA_BLOCK_HEIGHT *
> -		       fb->format->cpp[0] * (x_offset_in_blocks + 1);
> +		offset = pitch * y_offset_in_blocks +
> +			 AFBC_DATA_BLOCK_WIDTH * AFBC_DATA_BLOCK_HEIGHT
> *
> +			 fb->format->cpp[0] * (x_offset_in_blocks + 1);
> +
> +		/*
> +		 * Using dma_addr_t variable to calculate with
> multiplier of different types,
> +		 * for example: addr += pitch * y_offset_in_blocks;
> +		 * may cause coverity issue with unintentional
> overflow.
> +		 */
> +		addr = addr + hdr_size + offset;
>  	}
>  
>  	mtk_plane_state->pending.enable = true;