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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Florian Weimer <fweimer@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Randy Dunlap <rdunlap@infradead.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Ingo Molnar <mingo@kernel.org>,
	David Laight <David.Laight@aculab.com>,
	Ian Abbott <abbotti@mev.co.uk>,
	linux-input <linux-input@vger.kernel.org>,
	linux-btrfs <linux-btrfs@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH v5 0/2] Remove false-positive VLAs when using max()
Date: Sat, 17 Mar 2018 17:55:24 -0500	[thread overview]
Message-ID: <20180317225524.vy7vpopgiwjcp2sa@treble> (raw)
In-Reply-To: <CAGXu5jJ=ZYpf=30H6hsWn-R-CEVYAgVMHxjmoLUC00QYq0r17g@mail.gmail.com>

On Sat, Mar 17, 2018 at 01:07:32PM -0700, Kees Cook wrote:
> On Sat, Mar 17, 2018 at 11:52 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> > So the above is completely insane, bit there is actually a chance that
> > using that completely crazy "x -> sizeof(char[x])" conversion actually
> > helps, because it really does have a (very odd) evaluation-time
> > change.  sizeof() has to be evaluated as part of the constant
> > expression evaluation, in ways that "__builtin_constant_p()" isn't
> > specified to be done.
> >
> > But it is also definitely me grasping at straws. If that doesn't work
> > for 4.4, there's nothing else I can possibly see.
> 
> No luck! :( gcc 4.4 refuses to play along. And, hilariously, not only
> does it not change the complaint about __builtin_choose_expr(), it
> also thinks that's a VLA now.
> 
> ./include/linux/mm.h: In function ‘get_mm_hiwater_rss’:
> ./include/linux/mm.h:1567: warning: variable length array is used
> ./include/linux/mm.h:1567: error: first argument to
> ‘__builtin_choose_expr’ not a constant
> 
> 6.8 is happy with it (of course).
> 
> I do think the earlier version (without the
> sizeof-hiding-builting_constant_p) provides a template for a
> const_max() that both you and Rasmus would be happy with, though!

I thought we were dropping support for 4.4 (for other reasons).  Isn't
it 4.6 we should be looking at?

-- 
Josh

  reply	other threads:[~2018-03-17 22:55 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-16  4:25 [PATCH v5 0/2] Remove false-positive VLAs when using max() Kees Cook
2018-03-16  4:25 ` [PATCH v5 1/2] kernel.h: Introduce const_max_t() for VLA removal Kees Cook
2018-03-16  4:25 ` [PATCH v5 2/2] Remove false-positive VLAs when using max() Kees Cook
2018-03-19 10:45   ` Andrey Ryabinin
2018-03-16 11:47 ` [PATCH v5 0/2] " Florian Weimer
2018-03-16 17:29   ` Linus Torvalds
2018-03-16 17:32     ` Florian Weimer
2018-03-16 17:44     ` David Laight
2018-03-16 20:25       ` Linus Torvalds
2018-03-16 17:55     ` Al Viro
2018-03-16 18:14       ` Al Viro
2018-03-16 19:27       ` Linus Torvalds
2018-03-16 20:03         ` Miguel Ojeda
2018-03-16 20:14           ` Linus Torvalds
2018-03-16 20:19             ` Linus Torvalds
2018-03-17  0:48             ` Miguel Ojeda
2018-03-17  1:49             ` Miguel Ojeda
2018-03-16 20:12         ` Al Viro
2018-03-16 20:15           ` Linus Torvalds
2018-03-16 20:18             ` Al Viro
2018-03-17  7:27         ` Kees Cook
2018-03-17 18:52           ` Linus Torvalds
2018-03-17 20:07             ` Kees Cook
2018-03-17 22:55               ` Josh Poimboeuf [this message]
2018-03-20 23:23               ` Linus Torvalds
2018-03-20 23:26                 ` Linus Torvalds
2018-03-21  0:05                   ` Al Viro
2018-03-22 15:01                 ` Kees Cook
2018-03-22 15:13                   ` David Laight
2018-03-22 17:04                   ` Linus Torvalds
2018-03-18 21:13             ` Rasmus Villemoes
2018-03-18 21:33               ` Linus Torvalds
2018-03-18 22:59                 ` Rasmus Villemoes
2018-03-18 23:36                   ` Linus Torvalds
2018-03-19  9:43                     ` David Laight
2018-03-19 23:29                       ` Linus Torvalds
2018-03-20  3:10                         ` Arnd Bergmann

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