linux-kernel - Re: [PATCH v1 1/2] Add the initify gcc plugin

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Date:	Wed, 29 Jun 2016 07:50:25 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
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,
	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	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>,
	jlayton@...chiereds.net, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v1 1/2] Add the initify gcc plugin

On Tue, Jun 28, 2016 at 2:05 PM, Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
> On Tue, Jun 28 2016, Emese Revfy <re.emese@...il.com> wrote:
>
>> The kernel already has a mechanism to free up code and data memory that
>> is only used during kernel or module initialization.
>> This plugin will teach the compiler to find more such code and data that
>> can be freed after initialization.
>> It has two passes. The first one tries to find all functions that
>> can be become __init/__exit. The second one moves string constants
>> (local variables and function string arguments marked by
>> the nocapture attribute) only referenced in __init/__exit functions
>> to the __initconst/__exitconst sections.
>> It reduces memory usage. This plugin can be useful for embedded systems.
>
> May I suggest, as a followup patch, a debug option/plugin parameter to
> put the strings in a section which will not be reaped after init, but
> just marked inaccessible, with graceful handling of bad accesses (print
> a big fat warning, make the page(s) readable, continue)?

Is there a clean way to do this that isn't arch-specific?

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security