linux-kernel - RE: [PATCH v5 0/2] Remove false-positive VLAs when using max()

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Date:   Thu, 22 Mar 2018 15:13:10 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kees Cook' <keescook@...omium.org>,
        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>, 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()

From: Kees Cook
> Sent: 22 March 2018 15:01
...
> >   /* Glory to Martin Uecker <Martin.Uecker@....uni-goettingen.de> */
> >   #define __is_constant(a) \
> >         (sizeof(int) == sizeof(*(1 ? ((void*)((a) * 0l)) : (int*)1)))
...
> So, this time it's not a catastrophic failure with gcc 4.4. Instead it
> fails in 11 distinct places:
...
> Seems like it doesn't like void * arguments:
> 
> mm/percpu.c:
>                 void *ptr;
> ...
>                 base = min(ptr, base);

Try adding (unsigned long) before the (a).

	David