netdev - Re: [PATCH v5 0/2] Remove false-positive VLAs when using max()

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Message-ID: <CAGXu5jJmAAgaq3VCsUN2yjpHLSc7P-kNrM_4c4cqP=ysFcETXA@mail.gmail.com>
Date:   Sat, 17 Mar 2018 00:27:02 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Florian Weimer <fweimer@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Randy Dunlap <rdunlap@...radead.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        Ian Abbott <abbotti@....co.uk>,
        linux-input <linux-input@...r.kernel.org>,
        linux-btrfs <linux-btrfs@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v5 0/2] Remove false-positive VLAs when using max()

On Fri, Mar 16, 2018 at 12:27 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> Kees - is there some online "gcc-4.4 checker" somewhere? This does
> seem to work with my gcc. I actually tested some of those files you
> pointed at now.

Unfortunately my 4.4 test fails quickly:

./include/linux/jiffies.h: In function ‘jiffies_delta_to_clock_t’:
./include/linux/jiffies.h:444: error: first argument to
‘__builtin_choose_expr’ not a constant

static inline clock_t jiffies_delta_to_clock_t(long delta)
{
        return jiffies_to_clock_t(max(0L, delta));
}

I think this is the same problem of using __builtin_constant_p() in
4.4 that we hit earlier? :(

-Kees

-- 
Kees Cook
Pixel Security