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

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Message-ID: <BY5PR11MB4182B94E480EFACBF817DFFF8CF50@BY5PR11MB4182.namprd11.prod.outlook.com>
Date:   Mon, 30 Nov 2020 22:19:13 +0000
From:   "Chrisanthus, Anitha" <anitha.chrisanthus@...el.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        "Dea, Edmund J" <edmund.j.dea@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "Sam Ravnborg" <sam@...nborg.org>
CC:     Arnd Bergmann <arnd@...db.de>, lkp <lkp@...el.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] drm/kmb: fix array bounds warning

Hi Arnd,
Thanks for your patch.

> -----Original Message-----
> From: Arnd Bergmann <arnd@...nel.org>
> Sent: Sunday, November 29, 2020 12:09 PM
> To: Chrisanthus, Anitha <anitha.chrisanthus@...el.com>; Dea, Edmund J
> <edmund.j.dea@...el.com>; David Airlie <airlied@...ux.ie>; Daniel Vetter
> <daniel@...ll.ch>; Sam Ravnborg <sam@...nborg.org>
> Cc: Arnd Bergmann <arnd@...db.de>; lkp <lkp@...el.com>; dri-
> devel@...ts.freedesktop.org; linux-kernel@...r.kernel.org
> Subject: [PATCH] drm/kmb: fix array bounds warning
> 
> From: Arnd Bergmann <arnd@...db.de>
> 
> 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@...el.com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  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@...el.com>
>  	switch (plane_id) {
>  	case LAYER_0:
>  		kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL1_ENABLE;
> --
> 2.27.0