linux-kernel - Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 25 Nov 2015 10:54:08 -0800
From:	Kees Cook <keescook@...omium.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Mathias Krause <minipli@...glemail.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86-ml <x86@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Michael Ellerman <mpe@...erman.id.au>,
	linux-arch <linux-arch@...r.kernel.org>,
	PaX Team <pageexec@...email.hu>,
	Emese Revfy <re.emese@...il.com>
Subject: Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory

On Wed, Nov 25, 2015 at 9:31 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 11/25/15 01:13, Mathias Krause wrote:
>>
>> While having that annotation makes perfect sense, not only from a
>> security perspective but also from a micro-optimization point of view
>> (much like the already existing __read_mostly annotation), it has its
>> drawbacks. Violating the "r/o after init" rule by writing to such
>> annotated variables from non-init code goes unnoticed as far as it
>> concerns the toolchain. Neither the compiler nor the linker will flag
>> that incorrect use. It'll just trap at runtime and that's bad.
>>
>> I myself had some educating experience seeing my machine triple fault
>> when resuming from a S3 sleep. The root cause was a variable that was
>> annotated __read_only but that was (unnecessarily) modified during CPU
>> bring-up phase. Debugging that kind of problems is sort of a PITA, you
>> could imagine.
>>
>> So, prior extending the usage of the __read_only annotation some
>> toolchain support is needed. Maybe a gcc plugin that'll warn/error on
>> code that writes to such a variable but is not __init itself. The
>> initify and checker plugins from the PaX patch might be worth to look
>> at for that purpose, as they're doing similar things already. Adding
>> such a check to sparse might be worth it, too.
>> A modpost check probably won't work as it's unable to tell if it's a
>> legitimate access (r/o) or a violation (/w access). So the gcc plugin
>> is the way to go, IMHO.
>>
>
> We should not wait for compile-time support, that doesn't make any
> sense.  What would be useful would be a way to override this on the
> command line -- that way, if disabling RO or RO-after-init memory makes
> something work, we have an instant diagnosis.

Seems easiest to have an arg just skip calling mark_rodata_ro(). I can add that.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/