Walking the dram->cs array was seen as accesses beyond the first array
item by the compiler. Instead, use the array index directly. This allows
for run-time bounds checking under CONFIG_UBSAN_BOUNDS as well. Seen
with GCC 13 with -fstrict-flex-arrays:

../sound/soc/kirkwood/kirkwood-dma.c: In function
'kirkwood_dma_conf_mbus_windows.constprop':
../sound/soc/kirkwood/kirkwood-dma.c:90:24: warning: array subscript 0 is outside array bounds of 'const struct mbus_dram_window[0]' [-Warray-bounds=]
   90 |                 if ((cs->base & 0xffff0000) < (dma & 0xffff0000)) {
      |                      ~~^~~~~~

Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: alsa-devel@alsa-project.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 sound/soc/kirkwood/kirkwood-dma.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/soc/kirkwood/kirkwood-dma.c b/sound/soc/kirkwood/kirkwood-dma.c
index 700a18561a94..640cebd2983e 100644
--- a/sound/soc/kirkwood/kirkwood-dma.c
+++ b/sound/soc/kirkwood/kirkwood-dma.c
@@ -86,7 +86,7 @@ kirkwood_dma_conf_mbus_windows(void __iomem *base, int win,
 
 	/* try to find matching cs for current dma address */
 	for (i = 0; i < dram->num_cs; i++) {
-		const struct mbus_dram_window *cs = dram->cs + i;
+		const struct mbus_dram_window *cs = &dram->cs[i];
 		if ((cs->base & 0xffff0000) < (dma & 0xffff0000)) {
 			writel(cs->base & 0xffff0000,
 				base + KIRKWOOD_AUDIO_WIN_BASE_REG(win));
-- 
2.34.1

On Fri, 27 Jan 2023 14:41:29 -0800, Kees Cook wrote:
> Walking the dram->cs array was seen as accesses beyond the first array
> item by the compiler. Instead, use the array index directly. This allows
> for run-time bounds checking under CONFIG_UBSAN_BOUNDS as well. Seen
> with GCC 13 with -fstrict-flex-arrays:
> 
> ../sound/soc/kirkwood/kirkwood-dma.c: In function
> 'kirkwood_dma_conf_mbus_windows.constprop':
> ../sound/soc/kirkwood/kirkwood-dma.c:90:24: warning: array subscript 0 is outside array bounds of 'const struct mbus_dram_window[0]' [-Warray-bounds=]
>    90 |                 if ((cs->base & 0xffff0000) < (dma & 0xffff0000)) {
>       |                      ~~^~~~~~
> 
> [...]

Applied to

   broonie/sound.git for-next

Thanks!

[1/1] ASoC: kirkwood: Iterate over array indexes instead of using pointer math
      commit: b3bcedc0402fcdc5c8624c433562d9d1882749d8

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark