linux/init
Yury Norov 8e5bd4eadd gcc: disable '-Warray-bounds' for gcc-9
'-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 b44759705f ("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
Fixes: b44759705f ("bitmap: make bitmap_{get,set}_value8() use bitmap_{read,write}()")
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>
2024-06-15 10:43:04 -07:00
..
.gitignore
build-version
calibrate.c
do_mounts_initrd.c initrd: remove the now superfluous sentinel element from ctl_table array 2024-04-25 21:07:05 -07:00
do_mounts_rd.c
do_mounts.c init: replace deprecated strncpy with strscpy_pad 2024-04-30 10:34:29 -07:00
do_mounts.h init: flush async file closing 2024-02-08 18:41:03 +01:00
init_task.c Livepatching changes for 6.10 2024-05-15 13:07:49 -07:00
initramfs.c Merge 6.9-rc5 into driver-core-next 2024-04-23 13:27:43 +02:00
Kconfig gcc: disable '-Warray-bounds' for gcc-9 2024-06-15 10:43:04 -07:00
main.c Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
Makefile Makefile: remove redundant tool coverage variables 2024-05-14 23:35:48 +09:00
noinitramfs.c
version-timestamp.c
version.c init/version.c: Replace strlcpy with strscpy 2023-09-22 09:50:56 -07:00