linux-kernel - Re: lib/crypto/chacha.c:65:1: warning: the frame size of 1604 bytes is larger than 1024 bytes

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Date:   Thu, 27 Aug 2020 10:55:32 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Ard Biesheuvel <ardb@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        kernel test robot <lkp@...el.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        kbuild-all@...ts.01.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>
Subject: Re: lib/crypto/chacha.c:65:1: warning: the frame size of 1604 bytes
 is larger than 1024 bytes

On Thu, Aug 27, 2020 at 10:34 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> How are you guys testing? I have UBSAN and GCOV on, and don't see
> crazy frames on either i386 or x86-64.

Oh, never mind. I also have COMPILE_TEST on, so it ends up disabling
GCOV_PROFILE_ALL and UBSAN_SANITIZE_ALL.

And yeah, this seems to be a gcc bug. It generates a ton of stack
slots for temporaries. It's -fsanitize=object-size that seems to do
it.

And "-fstack-reuse=all" doesn't seem to make any difference.

So I think

 (a) our stack size check is good to catch this

 (b) gcc and -fsanitize=object-size is basically an unusable combination

and it's not a bug in the kernel.

                Linus