RE: [PATCH] drm/kmb: fix array bounds warning

[Chrisanthus, Anitha]

Hi Arnd,
Thanks for your patch.

> -----Original Message-----
> From: Arnd Bergmann <arnd@xxxxxxxxxx>
> Sent: Sunday, November 29, 2020 12:09 PM
> To: Chrisanthus, Anitha <anitha.chrisanthus@xxxxxxxxx>; Dea, Edmund J
> <edmund.j.dea@xxxxxxxxx>; David Airlie <airlied@xxxxxxxx>; Daniel Vetter
> <daniel@xxxxxxxx>; Sam Ravnborg <sam@xxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>; lkp <lkp@xxxxxxxxx>; dri-
> devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: [PATCH] drm/kmb: fix array bounds warning
> 
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> gcc warns about an out-of-bounds access when the using nonzero
> values for 'plane_id' on kmb->plane_status:
> 
> drivers/gpu/drm/kmb/kmb_plane.c: In function 'kmb_plane_atomic_disable':
> drivers/gpu/drm/kmb/kmb_plane.c:128:20: warning: array subscript 3 is
> above array bounds of 'struct layer_status[1]' [-Warray-bounds]
>   128 |   kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL2_ENABLE;
>       |   ~~~~~~~~~~~~~~~~~^~~~~~~~~~
> drivers/gpu/drm/kmb/kmb_plane.c:125:20: warning: array subscript 2 is
> above array bounds of 'struct layer_status[1]' [-Warray-bounds]
>   125 |   kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL1_ENABLE;
>       |   ~~~~~~~~~~~~~~~~~^~~~~~~~~~
> drivers/gpu/drm/kmb/kmb_plane.c:122:20: warning: array subscript 1 is
> above array bounds of 'struct layer_status[1]' [-Warray-bounds]
>   122 |   kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL2_ENABLE;
> 
> Having the array truncated to one entry seems intentional, so add
> a range check before indexing it to make it clearer what is going
> on and shut up the warning.
> 
> I received the warning from the kernel test robot after a private
> patch that turns on Warray-bounds unconditionally.
> 
> Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  drivers/gpu/drm/kmb/kmb_plane.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/kmb/kmb_plane.c
> b/drivers/gpu/drm/kmb/kmb_plane.c
> index 8448d1edb553..be8eea3830c1 100644
> --- a/drivers/gpu/drm/kmb/kmb_plane.c
> +++ b/drivers/gpu/drm/kmb/kmb_plane.c
> @@ -114,6 +114,9 @@ static void kmb_plane_atomic_disable(struct
> drm_plane *plane,
> 
>  	kmb = to_kmb(plane->dev);
> 
> +	if (WARN_ON(plane_id >= KMB_MAX_PLANES))
> +		return;
> +
Looks good.

Reviewed-by: Anitha Chrisanthus <anitha.chrisanthus@xxxxxxxxx>
>  	switch (plane_id) {
>  	case LAYER_0:
>  		kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL1_ENABLE;
> --
> 2.27.0