[PATCH u-boot-dm 03/39] regmap: fix a serious pointer casting bug

[Bin Meng]

On Sun, Mar 7, 2021 at 12:26 PM Marek Behún <marek.behun at nic.cz> wrote:
>
> There is a serious bug in regmap_read() and regmap_write() functions
> where an uint pointer is cast to (void *) which is then cast to (u8 *),
> (u16 *), (u32 *) or (u64 *), depending on register width of the map.
>
> For example given a regmap with 16-bit register width the code
>         int val = 0x12340000;
>         regmap_read(map, 0, &val);
> only changes the lower 16 bits of val on little-endian machines.
> The upper 16 bits will remain 0x1234.
>
> Nobody noticed this probably because this bug can be triggered with
> regmap_write() only on big-endian architectures (which are not used by
> many people anymore), and on little endian this bug has consequences
> only if register width is 8 or 16 bits and also the memory place to
> which regmap_read() should store it's result has non-zero upper bits,
> which it seems doesn't happen anywhere in U-Boot normally. CI managed to
> trigger this bug in unit test of dm_test_devm_regmap_field when compiled
> for sandbox_defconfig using LTO.
>
> Fix this simply by taking into account that regmap_raw_read() and
> regmap_raw_write() behave as if the data given to these functions were
> in little-endian format, i.e. use cpu_to_le32() / le32_to_cpu(). In
> regmap_read() also zero out the space so that we don't get invalid
> result if regmap_raw_read() does not fill the whole object.
>
> Signed-off-by: Marek Behún <marek.behun at nic.cz>
> Reviewed-by: Simon Glass <sjg at chromium.org>
> Reviewed-by: Heiko Schocher <hs at denx.de>
> ---
>  drivers/core/regmap.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>

Reviewed-by: Bin Meng <bmeng.cn at gmail.com>

Maybe we can create a test case on QEMU PPC to cover the big endian targets?

Regards,
Bin