Re: [PATCH net-next v5 02/20] zinc: introduce minimal cryptography library

From: Jason A. Donenfeld
Date: Tue Sep 25 2018 - 10:29:22 EST

Hey Arnd,

On Tue, Sep 25, 2018 at 9:18 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> I think I misread your earlier sentence and thought you had said the
> exact opposite.
> For confirmation, I've downloaded your git tree and built it with my
> collection of compilers (gcc-4.6 through 8.1) and tried building it
> in various configurations. Nothing alarming stood out, the only
> thing that I think would might warrant some investigation is this one:
> lib/zinc/curve25519/curve25519-hacl64.h: In function 'curve25519_generic':
> lib/zinc/curve25519/curve25519-hacl64.h:785:1: warning: the frame size
> of 1536 bytes is larger than 500 bytes [-Wframe-larger-than=]
> Without KASAN, this takes 832 bytes, which is still more than it should
> use from a look at the source code.
> I first suspected some misoptimization around the get/put_unaligned_le64()
> calls, but playing around with it some more led me to this patch:

Excellent detective work. Thanks for spotting that before I had a time
to respond here. I'll also send that same fix to the HACL* team at
INRIA, so they can add it as a heuristic.