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

From: Kees Cook <keescook@chromium.org>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Emese Revfy <re.emese@gmail.com>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	PaX Team <pageexec@freemail.hu>,
	Brad Spengler <spender@grsecurity.net>,
	Michal Marek <mmarek@suse.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	linux-kbuild <linux-kbuild@vger.kernel.org>,
	minipli@ld-linux.so, Catalin Marinas <catalin.marinas@arm.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	David Brown <david.brown@linaro.org>,
	"benh@kernel.crashing.org" <benh@kernel.crashing.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jeff Layton <jlayton@poochiereds.net>,
	Arnd Bergmann <arnd@arndb.de>, Sam Ravnborg <sam@ravnborg.org>,
	Karsten Keil <isdn@linux-pingi.de>
Subject: Re: [PATCH v2 1/3] Add the initify gcc plugin
Date: Tue, 12 Jul 2016 18:38:47 -0400	[thread overview]
Message-ID: <CAGXu5j+99nc9s-ci46s3r_CU5-6O6JeHERcW3mYRtnP71871rw@mail.gmail.com> (raw)
In-Reply-To: <20160712220853.GU1041@n2100.armlinux.org.uk>

On Tue, Jul 12, 2016 at 6:08 PM, Russell King - ARM Linux
<linux@armlinux.org.uk> wrote:
> On Tue, Jul 12, 2016 at 03:45:56PM -0400, Kees Cook wrote:
>> On Mon, Jul 4, 2016 at 7:40 PM, Emese Revfy <re.emese@gmail.com> wrote:
>> > If a function is called by __init and __exit functions as well then
>> > the plugin moves it to the __exit section. This causes false positive
>> > section mismatch errors/warnings that I don't know how to handle yet.
>>
>> Should the mismatch checker be updated to recognize this case? Without
>> the plugin, I assume these kinds of functions would only ever be
>> marked for __exit? If so, should the plugin strip the __init marking
>> and only add __exit?
>
> That sounds like a problem for architectures that still discard the
> __exit section at link time to reduce the size of the linked kernel
> image - though, obviously, if using the plugin results in a smaller
> kernel image _with_ the exit sections, then there's a net benefit
> size-wise.

Ah right, __exit is dropped for non-modular builds. So, for "both
__init and __exit" it sounds like the behavior depends on the build:

- if modular: remove __init marking (since we need it after init)
- if non-modular: remove __exit marking (since we'll never call exit)

Is this something the build itself (rather than the plugin) could
notice and fix up? Hmmm

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security