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Message-ID: <CAGXu5j+99nc9s-ci46s3r_CU5-6O6JeHERcW3mYRtnP71871rw@mail.gmail.com>
Date: Tue, 12 Jul 2016 18:38:47 -0400
From: Kees Cook <keescook@...omium.org>
To: Russell King - ARM Linux <linux@...linux.org.uk>
Cc: Emese Revfy <re.emese@...il.com>,
"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, 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 6:08 PM, Russell King - ARM Linux
<linux@...linux.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@...il.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
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