linux-kernel - RE: [PATCH v3] kernel.h: Skip single-eval logic on literals in min()/max()

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Date:   Wed, 14 Mar 2018 11:35:26 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kees Cook' <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Rasmus Villemoes" <linux@...musvillemoes.dk>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        "Tobin C. Harding" <me@...in.cc>,
        Steven Rostedt <rostedt@...dmis.org>,
        Jonathan Corbet <corbet@....net>, Chris Mason <clm@...com>,
        Josef Bacik <jbacik@...com>, David Sterba <dsterba@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        "Ingo Molnar" <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Borislav Petkov <bp@...e.de>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ian Abbott <abbotti@....co.uk>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Linux Btrfs <linux-btrfs@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: RE: [PATCH v3] kernel.h: Skip single-eval logic on literals in
 min()/max()

From: Kees Cook
> Sent: 13 March 2018 22:15
...
> I'll send a "const_max()" which will refuse to work on
> non-constant-values (so it doesn't get accidentally used on variables
> that could be exposed to double-evaluation), and will work for stack
> array declarations (to avoid the overly-sensitive -Wvla checks).

ISTR the definitions were of the form:
	char foo[max(sizeof (struct bah), sizeof (struct baz))];
This doesn't generate a 'foo' with the required alignment.
It would be much better to use a union.

	David