Re: [PATCH] drm: i915: display: intel_dmc: Fixes an unsigned subtraction which can never be negative.

[Lucas De Marchi]

On Thu, Dec 09, 2021 at 08:41:24PM -0800, Harshit Mogalapalli wrote:
> smatch warning:
> drivers/gpu/drm/i915/display/intel_dmc.c:601 parse_dmc_fw() warn:
> unsigned 'fw->size - offset' is never less than zero
>
> Firmware size is size_t and offset is u32. So the subtraction is
> unsigned which can never be less than zero.
>
> Fixes: 3d5928a168a9 ("drm/i915/xelpd: Pipe A DMC plugging")
> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>


Reviewed-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>

"s|drm: i915: display: Fixes|drm/i915/display: Fix|" in the subject,
that I will do when applying after we have the CI results.

thanks
Lucas De Marchi

> ---
> drivers/gpu/drm/i915/display/intel_dmc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dmc.c b/drivers/gpu/drm/i915/display/intel_dmc.c
> index 0cab18f972d1..2f477c298b00 100644
> --- a/drivers/gpu/drm/i915/display/intel_dmc.c
> +++ b/drivers/gpu/drm/i915/display/intel_dmc.c
> @@ -598,7 +598,7 @@ static void parse_dmc_fw(struct drm_i915_private *dev_priv,
> 			continue;
>
> 		offset = readcount + dmc->dmc_info[id].dmc_offset * 4;
> -		if (fw->size - offset < 0) {
> +		if (offset > fw->size) {
> 			drm_err(&dev_priv->drm, "Reading beyond the fw_size\n");
> 			continue;
> 		}
> --
> 2.27.0