linux-hardening - RE: [PATCH] drm/kmb: Avoid warnings on impossible plane

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Date:   Tue, 7 Sep 2021 17:32:53 +0000
From:   "Chrisanthus, Anitha" <anitha.chrisanthus@...el.com>
To:     Kees Cook <keescook@...omium.org>
CC:     "Dea, Edmund J" <edmund.j.dea@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Sam Ravnborg <sam@...nborg.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: RE: [PATCH] drm/kmb: Avoid warnings on impossible plane_id

Hi Kees,
This patch https://patchwork.kernel.org/project/dri-devel/patch/20210728003126.1425028-13-anitha.chrisanthus@intel.com/ is pushed to drm-misc-fixes. This change should fix the below warnings.

I apologize for all the inconveniences. 

Thanks,
Anitha

> -----Original Message-----
> From: Chrisanthus, Anitha
> Sent: Wednesday, August 25, 2021 1:44 PM
> To: Kees Cook <keescook@...omium.org>
> Cc: Dea, Edmund J <edmund.j.dea@...el.com>; David Airlie <airlied@...ux.ie>;
> Daniel Vetter <daniel@...ll.ch>; dri-devel@...ts.freedesktop.org; Sam
> Ravnborg <sam@...nborg.org>; linux-kernel@...r.kernel.org; linux-
> hardening@...r.kernel.org
> Subject: RE: [PATCH] drm/kmb: Avoid warnings on impossible plane_id
> 
> Hi Kees,
> Thanks for your patch.
> The switch statement is needed for multiple planes which is already approved
> in this patch series.
> https://patchwork.kernel.org/project/dri-
> devel/patch/20210728003126.1425028-13-anitha.chrisanthus@...el.com/
> 
> This patch has dependencies on the previous patches in this series, and we are
> waiting for reviews on those before this can be checked in.
> 
> Thanks,
> Anitha
> 
> > -----Original Message-----
> > From: Kees Cook <keescook@...omium.org>
> > Sent: Wednesday, August 25, 2021 11:18 AM
> > To: Chrisanthus, Anitha <anitha.chrisanthus@...el.com>
> > Cc: Kees Cook <keescook@...omium.org>; Dea, Edmund J
> > <edmund.j.dea@...el.com>; David Airlie <airlied@...ux.ie>; Daniel Vetter
> > <daniel@...ll.ch>; dri-devel@...ts.freedesktop.org; Sam Ravnborg
> > <sam@...nborg.org>; linux-kernel@...r.kernel.org; linux-
> > hardening@...r.kernel.org
> > Subject: [PATCH] drm/kmb: Avoid warnings on impossible plane_id
> >
> > KMB_MAX_PLANES is defined as 1, yet kmb_plane_atomic_disable() had
> code
> > for writing beyond 1. It is gated by a WARN_ON() that would skip it,
> > though, but under some compiler versions, poor Dead Code Elimination
> > wasn't optimizing away the unused switch cases, leading to array bounds
> > warnings when building with -Warray-bounds:
> >
> > drivers/gpu/drm/kmb/kmb_plane.c:135:20: warning: array subscript 3 is
> > above array bounds of 'struct layer_status[1]' [-Warray-bounds]
> > drivers/gpu/drm/kmb/kmb_plane.c:132:20: warning: array subscript 2 is
> > above array bounds of 'struct layer_status[1]' [-Warray-bounds]
> > drivers/gpu/drm/kmb/kmb_plane.c:129:20: warning: array subscript 1 is
> > above array bounds of 'struct layer_status[1]' [-Warray-bounds]
> >
> > Instead, just remove the switch statement entirely and adjust the index
> > type to match the struct "id" member.
> >
> > Cc: Anitha Chrisanthus <anitha.chrisanthus@...el.com>
> > Cc: Edmund Dea <edmund.j.dea@...el.com>
> > Cc: David Airlie <airlied@...ux.ie>
> > Cc: Daniel Vetter <daniel@...ll.ch>
> > Cc: dri-devel@...ts.freedesktop.org
> > Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> >  drivers/gpu/drm/kmb/kmb_plane.c | 18 ++----------------
> >  1 file changed, 2 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/kmb/kmb_plane.c
> > b/drivers/gpu/drm/kmb/kmb_plane.c
> > index ecee6782612d..3d46e756f2fe 100644
> > --- a/drivers/gpu/drm/kmb/kmb_plane.c
> > +++ b/drivers/gpu/drm/kmb/kmb_plane.c
> > @@ -113,7 +113,7 @@ static void kmb_plane_atomic_disable(struct
> > drm_plane *plane,
> >  				     struct drm_atomic_state *state)
> >  {
> >  	struct kmb_plane *kmb_plane = to_kmb_plane(plane);
> > -	int plane_id = kmb_plane->id;
> > +	unsigned char plane_id = kmb_plane->id;
> >  	struct kmb_drm_private *kmb;
> >
> >  	kmb = to_kmb(plane->dev);
> > @@ -121,21 +121,7 @@ static void kmb_plane_atomic_disable(struct
> > drm_plane *plane,
> >  	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;
> > -		break;
> > -	case LAYER_1:
> > -		kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL2_ENABLE;
> > -		break;
> > -	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;
> > -	}
> > -
> > +	kmb->plane_status[plane_id].ctrl = LCD_CTRL_VL1_ENABLE;
> >  	kmb->plane_status[plane_id].disable = true;
> >  }
> >
> > --
> > 2.30.2