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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Message-ID: <202008271229.C1E65D3565@keescook>
Date:   Thu, 27 Aug 2020 12:32:36 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        kernel test robot <lkp@...el.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        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 12:02:12PM -0700, Linus Torvalds wrote:
> On Thu, Aug 27, 2020 at 11:42 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > Do you mean you checked both gcc and clang and it was only a problem with gcc?
> 
> I didn't check with clang, but Arnd claimed it was fine.
> 
> > (If so, I can tweak the "depends" below...)
> 
> Ugh.
> 
> Instead of making the Makefile even uglier, why don't you just make
> this all be done in the Kconfig.
> 
> Also, I'm not seeing the point of your patch. You didn't actually
> change anything, you just made a new config variable with the same
> semantics as the old one.

Hmm? Yeah it did: it disallowed CONFIG_COMPILE_TEST, which you said was
the missing piece, I thought? (It's hardly the first time COMPILE_TEST
has collided unhappily with *SAN-ish things.)

> All of this should be thrown out, and this code should use the proper
> patterns for configuration entries in the Makefile, ie just
> 
>   ubsan-cflags-$(CONFIG_UBSAN_OBJECT_SIZE) += -fsanitize=object-size

Yeah, that would be a better pattern for sure.

> and the Kconfig file is the thing that should check if that CC option
> exists with
> 
>   config UBSAN_OBJECT_SIZE
>         bool "Check for accesses beyond known object sizes"
>         default UBSAN
>         depends on CLANG  # gcc makes a mess of it
>         depends on $(cc-option,-fsanitize-coverage=trace-pc)

Yup, for sure. I've only recently started poking at the ubsan stuff. I
can clean it up better.

> Doesn't that all look much cleaner?

Yup!

-- 
Kees Cook