[PATCH] drm/kmb: Avoid warnings on impossible plane_id

[PATCH] drm/kmb: Avoid warnings on impossible plane_id

[Kees Cook]

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@intel.com>
Cc: Edmund Dea <edmund.j.dea@intel.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
Signed-off-by: Kees Cook <keescook@chromium.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

RE: [PATCH] drm/kmb: Avoid warnings on impossible plane_id

[Chrisanthus, Anitha]

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@intel.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@chromium.org>
> Sent: Wednesday, August 25, 2021 11:18 AM
> To: Chrisanthus, Anitha <anitha.chrisanthus@intel.com>
> Cc: Kees Cook <keescook@chromium.org>; Dea, Edmund J
> <edmund.j.dea@intel.com>; David Airlie <airlied@linux.ie>; Daniel Vetter
> <daniel@ffwll.ch>; dri-devel@lists.freedesktop.org; Sam Ravnborg
> <sam@ravnborg.org>; linux-kernel@vger.kernel.org; linux-
> hardening@vger.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@intel.com>
> Cc: Edmund Dea <edmund.j.dea@intel.com>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: dri-devel@lists.freedesktop.org
> Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
> Signed-off-by: Kees Cook <keescook@chromium.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

RE: [PATCH] drm/kmb: Avoid warnings on impossible plane_id

[Chrisanthus, Anitha]

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@chromium.org>
> Cc: Dea, Edmund J <edmund.j.dea@intel.com>; David Airlie <airlied@linux.ie>;
> Daniel Vetter <daniel@ffwll.ch>; dri-devel@lists.freedesktop.org; Sam
> Ravnborg <sam@ravnborg.org>; linux-kernel@vger.kernel.org; linux-
> hardening@vger.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@intel.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@chromium.org>
> > Sent: Wednesday, August 25, 2021 11:18 AM
> > To: Chrisanthus, Anitha <anitha.chrisanthus@intel.com>
> > Cc: Kees Cook <keescook@chromium.org>; Dea, Edmund J
> > <edmund.j.dea@intel.com>; David Airlie <airlied@linux.ie>; Daniel Vetter
> > <daniel@ffwll.ch>; dri-devel@lists.freedesktop.org; Sam Ravnborg
> > <sam@ravnborg.org>; linux-kernel@vger.kernel.org; linux-
> > hardening@vger.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@intel.com>
> > Cc: Edmund Dea <edmund.j.dea@intel.com>
> > Cc: David Airlie <airlied@linux.ie>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Cc: dri-devel@lists.freedesktop.org
> > Fixes: 7f7b96a8a0a1 ("drm/kmb: Add support for KeemBay Display")
> > Signed-off-by: Kees Cook <keescook@chromium.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

Re: [PATCH] drm/kmb: Avoid warnings on impossible plane_id

[Kees Cook]

On Tue, Sep 07, 2021 at 05:32:53PM +0000, Chrisanthus, Anitha wrote:
> 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. 

No worries; thanks for the heads-up!

(sfr, this change should fix the warning[1] uncovered by the KSPP tree now.)

-Kees

[1] https://lore.kernel.org/linux-next/20210830184429.1ee4b4d8@canb.auug.org.au/

-- 
Kees Cook