Subject: Re: linux-next: build failure after merge of the kspp tree

From: Kees Cook <[email-masked]>
Date: Mon, 24 Jan 2022 19:22:42 -0800

On Tue, Jan 25, 2022 at 02:02:21PM +1100, Stephen Rothwell wrote:
> Hi all,
> 
> On Tue, 25 Jan 2022 13:55:46 +1100 Stephen Rothwell <[email-masked]> wrote:
> >
> > After merging the kspp tree, today's linux-next build (powerpc
> > allyesconfig) failed like this:
> > 
> > drivers/gpu/drm/kmb/kmb_plane.c: In function 'kmb_plane_atomic_disable':
> > drivers/gpu/drm/kmb/kmb_plane.c:165:34: error: array subscript 3 is above array bounds of 'struct layer_status[2]' [-Werror=array-bounds]
> >   165 |                 kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL2_ENABLE;
> >       |                 ~~~~~~~~~~~~~~~~~^~~~~~~~~~
> > In file included from drivers/gpu/drm/kmb/kmb_plane.c:17:
> > drivers/gpu/drm/kmb/kmb_drv.h:61:41: note: while referencing 'plane_status'
> >    61 |         struct layer_status             plane_status[KMB_MAX_PLANES];
> >       |                                         ^~~~~~~~~~~~
> > drivers/gpu/drm/kmb/kmb_plane.c:162:34: error: array subscript 2 is above array bounds of 'struct layer_status[2]' [-Werror=array-bounds]
> >   162 |                 kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL1_ENABLE;
> >       |                 ~~~~~~~~~~~~~~~~~^~~~~~~~~~
> > In file included from drivers/gpu/drm/kmb/kmb_plane.c:17:
> > drivers/gpu/drm/kmb/kmb_drv.h:61:41: note: while referencing 'plane_status'
> >    61 |         struct layer_status             plane_status[KMB_MAX_PLANES];
> >       |                                         ^~~~~~~~~~~~
> > 
> > Exposed by commit
> > 
> >   4ba545781e20 ("Makefile: Enable -Warray-bounds")
> > 
> > Originally introduced by commmit
> > 
> >   7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
> > 
> > Maybe should have been fixed by
> > 
> >   c026565fe9be ("drm/kmb: Enable alpha blended second plane")

Yeah, that had fixed it at some point. :(

> > 
> > I have applied the following hack for now.
> 
> Actually, this one:
> 
> From: Stephen Rothwell <[email-masked]>
> Date: Tue, 25 Jan 2022 13:45:26 +1100
> Subject: [PATCH] hack for building with -Warray-bounds
> 
> Signed-off-by: Stephen Rothwell <[email-masked]>
> ---
>  drivers/gpu/drm/kmb/kmb_plane.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/kmb/kmb_plane.c b/drivers/gpu/drm/kmb/kmb_plane.c
> index 00404ba4126d..b54197920712 100644
> --- a/drivers/gpu/drm/kmb/kmb_plane.c
> +++ b/drivers/gpu/drm/kmb/kmb_plane.c
> @@ -158,12 +158,14 @@ static void kmb_plane_atomic_disable(struct drm_plane *plane,
>  	case LAYER_1:
>  		kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL2_ENABLE;
>  		break;
> +#if 0
>  	case LAYER_2:
>  		kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL1_ENABLE;
>  		break;
>  	case LAYER_3:
>  		kmb->plane_status[plane_id].ctrl = LCD_CTRL_GL2_ENABLE;
>  		break;
> +#endif
>  	}
>  
>  	kmb->plane_status[plane_id].disable = true;

Thanks!

The prior thread about this was here:
https://lore.kernel.org/lkml/[email-masked]/

-Kees

-- 
Kees Cook