[PATCH] drm/kmb: fix array bounds warning

[PATCH] drm/kmb: fix array bounds warning

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.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@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.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;
+
 	switch (plane_id) {
 	case LAYER_0:
 		kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL1_ENABLE;
-- 
2.27.0

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

[Chrisanthus, Anitha]

Hi Arnd,
Thanks for your patch.

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

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

[Sam Ravnborg]

Hi Anitha,
On Mon, Nov 30, 2020 at 10:19:13PM +0000, Chrisanthus, Anitha wrote:
> Hi Arnd,
> Thanks for your patch.
> 
> > -----Original Message-----
> > From: Arnd Bergmann <arnd@kernel.org>
> > Sent: Sunday, November 29, 2020 12:09 PM
> > To: Chrisanthus, Anitha <anitha.chrisanthus@intel.com>; Dea, Edmund J
> > <edmund.j.dea@intel.com>; David Airlie <airlied@linux.ie>; Daniel Vetter
> > <daniel@ffwll.ch>; Sam Ravnborg <sam@ravnborg.org>
> > Cc: Arnd Bergmann <arnd@arndb.de>; lkp <lkp@intel.com>; dri-
> > devel@lists.freedesktop.org; linux-kernel@vger.kernel.org
> > Subject: [PATCH] drm/kmb: fix array bounds warning
> > 
> > From: Arnd Bergmann <arnd@arndb.de>
> > 
> > gcc warns about an out-of-bounds access when the using nonzero
> > values for 'plane_id' on kmb->plane_status:
...

> Looks good.
> 
> Reviewed-by: Anitha Chrisanthus <anitha.chrisanthus@intel.com>

You wanted a little time to get comforable with dim, so I picked up this
patch and pushed it to drm-misc-next.

	Sam