[PATCH] ARM: crypto: work around gcc-15 warning

[Ard Biesheuvel]

On Tue, 10 Jun 2025 at 11:33, Arnd Bergmann <arnd at kernel.org> wrote:
>
> From: Arnd Bergmann <arnd at arndb.de>
>
> I get a very rare -Wstringop-overread warning with gcc-15 for one function
> in aesbs_ctr_encrypt():
>
> arch/arm/crypto/aes-neonbs-glue.c: In function 'ctr_encrypt':
> arch/arm/crypto/aes-neonbs-glue.c:212:1446: error: '__builtin_memcpy' offset [17, 2147483647] is out of the bounds [0, 16] of object 'buf' with type 'u8[16]' {aka 'unsigned char[16]'} [-Werror=array-bounds=]
>   212 |                         src = dst = memcpy(buf + sizeof(buf) - bytes,
> arch/arm/crypto/aes-neonbs-glue.c: In function 'ctr_encrypt':
> arch/arm/crypto/aes-neonbs-glue.c:218:17: error: 'aesbs_ctr_encrypt' reading 1 byte from a region of size 0 [-Werror=stringop-overread]
>   218 |                 aesbs_ctr_encrypt(dst, src, ctx->rk, ctx->rounds, bytes, walk.iv);
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> arch/arm/crypto/aes-neonbs-glue.c:218:17: note: referencing argument 2 of type 'const u8[0]' {aka 'const unsigned char[]'}
> arch/arm/crypto/aes-neonbs-glue.c:218:17: note: referencing argument 3 of type 'const u8[0]' {aka 'const unsigned char[]'}
> arch/arm/crypto/aes-neonbs-glue.c:218:17: note: referencing argument 6 of type 'u8[0]' {aka 'unsigned char[]'}
> arch/arm/crypto/aes-neonbs-glue.c:36:17: note: in a call to function 'aesbs_ctr_encrypt'
>    36 | asmlinkage void aesbs_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[],
>
> This could happen in theory if walk.nbytes is larger than INT_MAX and gets
> converted to a negative local variable.
>
> Keep the type unsigned like the orignal nbytes to be sure there is no
> integer overflow.
>
> Fixes: c8bf850e991a ("crypto: arm/aes-neonbs-ctr - deal with non-multiples of AES block size")
> Signed-off-by: Arnd Bergmann <arnd at arndb.de>

Acked-by: Ard Biesheuvel <ardb at kernel.org>

> ---
>  arch/arm/crypto/aes-neonbs-glue.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/crypto/aes-neonbs-glue.c b/arch/arm/crypto/aes-neonbs-glue.c
> index c60104dc1585..df5afe601e4a 100644
> --- a/arch/arm/crypto/aes-neonbs-glue.c
> +++ b/arch/arm/crypto/aes-neonbs-glue.c
> @@ -206,7 +206,7 @@ static int ctr_encrypt(struct skcipher_request *req)
>         while (walk.nbytes > 0) {
>                 const u8 *src = walk.src.virt.addr;
>                 u8 *dst = walk.dst.virt.addr;
> -               int bytes = walk.nbytes;
> +               unsigned int bytes = walk.nbytes;
>
>                 if (unlikely(bytes < AES_BLOCK_SIZE))
>                         src = dst = memcpy(buf + sizeof(buf) - bytes,
> --
> 2.39.5
>