Re: [PATCH 2/2] crypto: stm32 - Try to fix hash padding

From: Herbert Xu
Date: Sat Oct 07 2017 - 00:20:52 EST

On Tue, Sep 12, 2017 at 11:35:39AM +0200, Arnd Bergmann wrote:
> gcc warns that the length for the extra unaligned data in the hash
> function may be used unaligned. In theory this could happen if
> we pass a zero-length sg_list, or if sg_is_last() was never true:
> In file included from drivers/crypto/stm32/stm32-hash.c:23:
> drivers/crypto/stm32/stm32-hash.c: In function 'stm32_hash_one_request':
> include/uapi/linux/kernel.h:12:49: error: 'ncp' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> #define __KERNEL_DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
> Neither of these can happen in practice, so the warning is harmless.
> However while trying to suppress the warning, I noticed multiple
> problems with that code:
> - On big-endian kernels, we byte-swap the data like we do for
> register accesses, however this is a data stream and almost
> certainly needs to use a single writesl() instead of series
> of writel() to give the correct hash.
> - If the length is not a multiple of four bytes, we skip the
> last word entirely, since we write the truncated length
> using stm32_hash_set_nblw().
> - If we change the code to round the length up rather than
> down, the last bytes contain stale data, so it needs some
> form of padding.
> This tries to address all four problems, by correctly
> initializing the length to zero, using endian-safe copy
> functions, adding zero-padding and passing the padded length.
> I have done no testing on this patch, so please review
> carefully and if possible test with an unaligned length
> and big-endian kernel builds.
> Fixes: 8a1012d3f2ab ("crypto: stm32 - Support for STM32 HASH module")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Patch applied. Thanks.
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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