Re: + gcc-disable-warray-bounds-for-gcc-9.patch added to mm-hotfixes-unstable branch

[Yury Norov <yury.norov@gmail.com>]

On Thu, May 23, 2024 at 08:00:07PM -0700, Andrew Morton wrote:
> 
> The patch titled
>      Subject: gcc: disable '-Warray-bounds' for gcc-9
> has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
>      gcc-disable-warray-bounds-for-gcc-9.patch

Hi Andrew,

The script said you've applied it to mm-hotfixes, but the patch is
still not in mainline. Are you going to move it in this cycle, or
what are your plans on it?

Thanks,
Yury
 
> This patch will shortly appear at
>      https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/gcc-disable-warray-bounds-for-gcc-9.patch
> 
> This patch will later appear in the mm-hotfixes-unstable branch at
>     git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
> 
> The -mm tree is included into linux-next via the mm-everything
> branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> and is updated there every 2-3 working days
> 
> ------------------------------------------------------
> From: Yury Norov <yury.norov@gmail.com>
> Subject: gcc: disable '-Warray-bounds' for gcc-9
> Date: Wed, 22 May 2024 15:58:30 -0700
> 
> '-Warray-bounds' is already disabled for gcc-10+.  Now that we've merged
> bitmap_{read,write), I see the following error when building the kernel
> with gcc-9.4 (Ubuntu 20.04.4 LTS) for x86_64 allmodconfig:
> 
> drivers/pinctrl/pinctrl-cy8c95x0.c: In function `cy8c95x0_read_regs_mask.isra.0':
> include/linux/bitmap.h:756:18: error: array subscript [1, 288230376151711744] is outside array bounds of `long unsigned int[1]' [-Werror=array-bounds]
>   756 |  value_high = map[index + 1] & BITMAP_LAST_WORD_MASK(start + nbits);
>       |               ~~~^~~~~~~~~~~
> 
> The immediate reason is that the commit b44759705f7d ("bitmap: make
> bitmap_{get,set}_value8() use bitmap_{read,write}()") switched the
> bitmap_get_value8() to an alias of bitmap_read(); the same for 'set'.
> 
> Now; the code that triggers Warray-bounds, calls the function like this:
> 
>   #define MAX_BANK 8
>   #define BANK_SZ 8
>   #define MAX_LINE        (MAX_BANK * BANK_SZ)
>   DECLARE_BITMAP(tval, MAX_LINE); // 64-bit map: unsigned long tval[1]
> 
>   read_val |= bitmap_get_value8(tval, i * BANK_SZ) & ~bits;
> 
> bitmap_read() is implemented such that it may conditionally dereference a
> pointer beyond the boundary like this:
> 
> 	unsigned long offset = start % BITS_PER_LONG;
>         unsigned long space = BITS_PER_LONG - offset;
> 
>         if (space >= nbits)
>                 return (map[index] >> offset) & BITMAP_LAST_WORD_MASK(nbits);
> 
>         value_low = map[index] & BITMAP_FIRST_WORD_MASK(start);
>         value_high = map[index + 1] & BITMAP_LAST_WORD_MASK(start + nbits);
>         return (value_low >> offset) | (value_high << space);
> 
> In case of bitmap_get_value8(), it's impossible to violate the boundary
> because 'space >= nbits' is never the true for byte-aligned 8-bit access. 
> So, this is clearly a false-positive.
> 
> The same type of false-positives break my allmodconfig build in many
> places.  gcc-8, is clear, however.
> 
> Link: https://lkml.kernel.org/r/20240522225830.1201778-1-yury.norov@gmail.com
> Signed-off-by: Yury Norov <yury.norov@gmail.com>
> Cc: Alexander Lobakin <aleksander.lobakin@intel.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Nhat Pham <nphamcs@gmail.com>
> Cc: Petr Mladek <pmladek@suse.com>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Yoann Congal <yoann.congal@smile.fr>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  init/Kconfig |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/init/Kconfig~gcc-disable-warray-bounds-for-gcc-9
> +++ a/init/Kconfig
> @@ -883,7 +883,7 @@ config GCC10_NO_ARRAY_BOUNDS
>  
>  config CC_NO_ARRAY_BOUNDS
>  	bool
> -	default y if CC_IS_GCC && GCC_VERSION >= 100000 && GCC10_NO_ARRAY_BOUNDS
> +	default y if CC_IS_GCC && GCC_VERSION >= 90000 && GCC10_NO_ARRAY_BOUNDS
>  
>  # Currently, disable -Wstringop-overflow for GCC globally.
>  config GCC_NO_STRINGOP_OVERFLOW
> _
> 
> Patches currently in -mm which might be from yury.norov@gmail.com are
> 
> gcc-disable-warray-bounds-for-gcc-9.patch