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

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Date:   Mon, 25 Apr 2022 11:46:53 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Borislav Petkov <bp@...en8.de>, LKML <linux-kernel@...r.kernel.org>
Cc:     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 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>

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