Re: [PATCH] [v2] crypto: serpent - mark __serpent_setkey_sbox noinline

Eric Biggers
2019-06-18T18:05:31Z

On Tue, Jun 18, 2019 at 01:19:42PM +0200, Arnd Bergmann wrote:
> The same bug that gcc hit in the past is apparently now showing
> up with clang, which decides to inline __serpent_setkey_sbox:
>
> crypto/serpent_generic.c:268:5: error: stack frame size of 2112 bytes in function '__serpent_setkey' [-Werror,-Wframe-larger-than=]
>
> Marking it 'noinline' reduces the stack usage from 2112 bytes to
> 192 and 96 bytes, respectively, and seems to generate more
> useful object code.
>
> Fixes: c871c10e4ea7 ("crypto: serpent - improve __serpent_setkey with UBSAN")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> v2: style improvements suggested by Eric Biggers
> ---
> crypto/serpent_generic.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/crypto/serpent_generic.c b/crypto/serpent_generic.c
> index e57757904677..56fa665a4f01 100644
> --- a/crypto/serpent_generic.c
> +++ b/crypto/serpent_generic.c
> @@ -225,7 +225,13 @@
> x4 ^= x2; \
> })
>
> -static void __serpent_setkey_sbox(u32 r0, u32 r1, u32 r2, u32 r3, u32 r4, u32 *k)
> +/*
> + * both gcc and clang have misoptimized this function in the past,
> + * producing horrible object code from spilling temporary variables
> + * on the stack. Forcing this part out of line avoids that.
> + */
> +static noinline void __serpent_setkey_sbox(u32 r0, u32 r1, u32 r2,
> + u32 r3, u32 r4, u32 *k)
> {
> k += 100;
> S3(r3, r4, r0, r1, r2); store_and_load_keys(r1, r2, r4, r3, 28, 24);
> --
> 2.20.0
>

Reviewed-by: Eric Biggers <ebiggers@kernel.org>

- Eric