linux-kernel - Re: [PATCH v2 1/3] Add the initify gcc plugin

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Message-ID: <CAGXu5j+W2hZGkudskkmEn+beEN04qmg16-k7Rna-QRT3vyEW2g@mail.gmail.com>
Date:	Tue, 12 Jul 2016 16:05:45 -0400
From:	Kees Cook <keescook@...omium.org>
To:	Emese Revfy <re.emese@...il.com>
Cc:	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	Michal Marek <mmarek@...e.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	linux-kbuild <linux-kbuild@...r.kernel.org>, minipli@...linux.so,
	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	David Brown <david.brown@...aro.org>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	Arnd Bergmann <arnd@...db.de>, Sam Ravnborg <sam@...nborg.org>,
	Karsten Keil <isdn@...ux-pingi.de>
Subject: Re: [PATCH v2 1/3] Add the initify gcc plugin

On Tue, Jul 12, 2016 at 4:07 PM, Emese Revfy <re.emese@...il.com> wrote:
> On Tue, 12 Jul 2016 15:45:56 -0400
> Kees Cook <keescook@...omium.org> wrote:
>
>> On Mon, Jul 4, 2016 at 7:40 PM, Emese Revfy <re.emese@...il.com> wrote:
>> Thanks for sending this! I'll get it added to my tree for some 0day
>> build testing, and then get it into my -next tree.
>
> I'll send a new patch set soon. I'm working on some fixes and
> I would like to implement the handling of return uses to increase the coverage
> (which decreases because of the bug fixes :) ).
> So please hold off with testing until the next patch.

Okay, cool. I'll just do some simple tests with what I have so I can
feel like I understand its intended use, etc. :)

One change I made was to add this comment in compiler-gcc.h for people
that become curious about __nocapture and go looking for its
definition (please feel free to adjust for accuracy, etc):


/*
 * The initify gcc-plugin attempts to identify const arguments that are only
 * used during init (see __init), so they can be moved to the .init.rodata
 * section. If an argument is passed to a non-init function, it must
 * normally be assumed that such an argument has been captured by that
 * function and may be used in the future when .init has been unmapped from
 * memory. In order to identify functions that are confirmed to not capture
 * their arguments, the __nocapture() attribute is used so that initify can
 * better identify candidate variables.
 */
#ifdef INITIFY_PLUGIN
# define __nocapture(...) __attribute__((nocapture(__VA_ARGS__)))
#endif


-Kees

-- 
Kees Cook
Chrome OS & Brillo Security