Re: [PATCH] drm: Prevent sign extension on hdisplay and vdisplay

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Tue, Oct 07, 2025 at 03:36:46PM +0000, Jonathan Cavitt wrote:
> Some functions in drm multiply hdisplay and vdisplay with a third
> factor, which can result in a sign extension according to static
> analysis due to an implicit s32 promotion.  Use a cast to u32 to
> prevent this.
> 
> Suggested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Signed-off-by: Krzystof Karas <krzysztof.karas@intel.com>
> Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
> Cc: Matthew Auld <matthew.auld@intel.com>
> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Andi Shyti <andi.shyti@intel.com>
> ---
>  drivers/gpu/drm/drm_gem_vram_helper.c | 2 +-
>  drivers/gpu/drm/drm_mipi_dbi.c        | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
> index 90760d0ca071..0bec6f66682b 100644
> --- a/drivers/gpu/drm/drm_gem_vram_helper.c
> +++ b/drivers/gpu/drm/drm_gem_vram_helper.c
> @@ -967,7 +967,7 @@ drm_vram_helper_mode_valid_internal(struct drm_device *dev,
>  
>  	max_fbpages = (vmm->vram_size / 2) >> PAGE_SHIFT;
>  
> -	fbsize = mode->hdisplay * mode->vdisplay * max_bpp;
> +	fbsize = (u32)mode->hdisplay * mode->vdisplay * max_bpp;
>  	fbpages = DIV_ROUND_UP(fbsize, PAGE_SIZE);
>  
>  	if (fbpages > max_fbpages)
> diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
> index e33c78fc8fbd..b488c91c20a5 100644
> --- a/drivers/gpu/drm/drm_mipi_dbi.c
> +++ b/drivers/gpu/drm/drm_mipi_dbi.c
> @@ -691,7 +691,7 @@ int mipi_dbi_dev_init(struct mipi_dbi_dev *dbidev,
>  		      const struct drm_simple_display_pipe_funcs *funcs,
>  		      const struct drm_display_mode *mode, unsigned int rotation)
>  {
> -	size_t bufsize = mode->vdisplay * mode->hdisplay * sizeof(u16);
> +	size_t bufsize = (u32)mode->vdisplay * mode->hdisplay * sizeof(u16);


Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

and pushed to drm-misc-next. No, I didn't considered to push it to -fixes
because it is a theoretical case that doesn't occur with real world pixels size.

>  
>  	dbidev->drm.mode_config.preferred_depth = 16;
>  
> -- 
> 2.43.0
>