linux-kernel - Re: [PATCH] fbdev: atyfb: fix array overflow

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Date:	Thu, 23 Jun 2016 03:28:25 +0300
From:	Ville Syrjälä <syrjala@....fi>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Tomi Valkeinen <tomi.valkeinen@...com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Luis R. Rodriguez" <mcgrof@...e.com>,
	Borislav Petkov <bp@...e.de>, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fbdev: atyfb: fix array overflow

On Wed, Jun 22, 2016 at 02:37:11PM +0200, Arnd Bergmann wrote:
> When building with CONFIG_UBSAN_SANITIZE_ALL on ARM, I get this
> gcc warning for atyfb:
> 
> drivers/video/fbdev/aty/atyfb_base.c: In function 'aty_bl_update_status':
> drivers/video/fbdev/aty/atyfb_base.c:167:33: warning: array subscript is above array bounds [-Warray-bounds]
> drivers/video/fbdev/aty/atyfb_base.c:152:26: warning: array subscript is above array bounds [-Warray-bounds]
> 
> Apparently the warning is correct and there is indeed an overflow,

Nope. All the LCD register indexes on the Rage LT (the only relevant
chip for this code path) should stay below the table size. At least
I can't see any place where we'd walk past the end.

> which was never caught. I could only reproduce this on ARM and
> have opened a bug against the compiler for the lack of warning.
> 
> This patch makes the array larger, so we cover all possible
> registers in the LCD controller without an overflow.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Link: https://bugs.linaro.org/show_bug.cgi?id=2349
> ---
>  drivers/video/fbdev/aty/atyfb_base.c | 2 +-
>  include/video/mach64.h               | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/aty/atyfb_base.c b/drivers/video/fbdev/aty/atyfb_base.c
> index 001d3d871800..36ffba152eab 100644
> --- a/drivers/video/fbdev/aty/atyfb_base.c
> +++ b/drivers/video/fbdev/aty/atyfb_base.c
> @@ -134,7 +134,7 @@
>  
>  #if defined(CONFIG_PM) || defined(CONFIG_PMAC_BACKLIGHT) || \
>  defined (CONFIG_FB_ATY_GENERIC_LCD) || defined(CONFIG_FB_ATY_BACKLIGHT)
> -static const u32 lt_lcd_regs[] = {
> +static const u32 lt_lcd_regs[LCD_REG_NUM] = {
>  	CNFG_PANEL_LG,
>  	LCD_GEN_CNTL_LG,
>  	DSTN_CONTROL_LG,
> diff --git a/include/video/mach64.h b/include/video/mach64.h
> index 89e91c0cb737..9f74e9e0aeb8 100644
> --- a/include/video/mach64.h
> +++ b/include/video/mach64.h
> @@ -1299,6 +1299,7 @@
>  #define APC_LUT_KL		0x38
>  #define APC_LUT_MN		0x39
>  #define APC_LUT_OP		0x3A
> +#define LCD_REG_NUM		0x3B /* total number */
>  
>  /* Values in LCD_GEN_CTRL */
>  #define CRT_ON                          0x00000001ul
> -- 
> 2.9.0
> 
> --
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-- 
Ville Syrjälä
syrjala@....fi
http://www.sci.fi/~syrjala/