linux-kernel - Re: [PATCH 04/11] drm/r128: Fix undefined behavior due to shift overflowing the constant

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Date:   Thu, 19 May 2022 15:05:08 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        LKML <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Alex Deucher <alexander.deucher@....com>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 04/11] drm/r128: Fix undefined behavior due to shift
 overflowing the constant

On Mon, Apr 25, 2022 at 11:46:53AM -0700, Randy Dunlap wrote:
> 
> 
> On 4/5/22 08:15, Borislav Petkov wrote:
> > From: Borislav Petkov <bp@...e.de>
> > 
> > Fix:
> > 
> >   drivers/gpu/drm/r128/r128_cce.c: In function ‘r128_do_init_cce’:
> >   drivers/gpu/drm/r128/r128_cce.c:417:2: error: case label does not reduce to an integer constant
> >     case R128_PM4_64BM_64VCBM_64INDBM:
> >     ^~~~
> >   drivers/gpu/drm/r128/r128_cce.c:418:2: error: case label does not reduce to an integer constant
> >     case R128_PM4_64PIO_64VCPIO_64INDPIO:
> >     ^~~~
> > 
> > See https://lore.kernel.org/r/YkwQ6%2BtIH8GQpuct@zn.tnic for the gory
> > details as to why it triggers with older gccs only.
> > 
> > Signed-off-by: Borislav Petkov <bp@...e.de>
> > Cc: David Airlie <airlied@...ux.ie>
> > Cc: Daniel Vetter <daniel@...ll.ch>
> > Cc: Alex Deucher <alexander.deucher@....com>
> > Cc: dri-devel@...ts.freedesktop.org
> 
> Reviewed-by: Randy Dunlap <rdunlap@...radead.org>

Pushed to drm-misc-next, thanks for patch&review.
-Daniel

> 
> Thanks.
> 
> > ---
> >  drivers/gpu/drm/r128/r128_drv.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/r128/r128_drv.h b/drivers/gpu/drm/r128/r128_drv.h
> > index 2e1bc01aa5c9..970e192b0d51 100644
> > --- a/drivers/gpu/drm/r128/r128_drv.h
> > +++ b/drivers/gpu/drm/r128/r128_drv.h
> > @@ -300,8 +300,8 @@ extern long r128_compat_ioctl(struct file *filp, unsigned int cmd,
> >  #	define R128_PM4_64PIO_128INDBM		(5  << 28)
> >  #	define R128_PM4_64BM_128INDBM		(6  << 28)
> >  #	define R128_PM4_64PIO_64VCBM_64INDBM	(7  << 28)
> > -#	define R128_PM4_64BM_64VCBM_64INDBM	(8  << 28)
> > -#	define R128_PM4_64PIO_64VCPIO_64INDPIO	(15 << 28)
> > +#	define R128_PM4_64BM_64VCBM_64INDBM	(8U  << 28)
> > +#	define R128_PM4_64PIO_64VCPIO_64INDPIO	(15U << 28)
> >  #	define R128_PM4_BUFFER_CNTL_NOUPDATE	(1  << 27)
> >  
> >  #define R128_PM4_BUFFER_WM_CNTL		0x0708
> 
> -- 
> ~Randy

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch