linux-kernel - Re: [PATCH 0/10] Add additional security checks when module loading is restricted

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Message-ID: <CAGXu5jKX0vFSaVT+nqUjR7K-p0dCo3Uw=6y17ShuEDkRoOJA8g@mail.gmail.com>
Date:	Mon, 19 Aug 2013 10:34:35 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Matthew Garrett <matthew.garrett@...ula.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Josh Boyer <jwboyer@...hat.com>
Subject: Re: [PATCH 0/10] Add additional security checks when module loading
 is restricted

On Mon, Aug 19, 2013 at 10:26 AM, Matthew Garrett
<matthew.garrett@...ula.com> wrote:
> We have two in-kernel mechanisms for restricting module loading - disabling
> it entirely, or limiting it to the loading of modules signed with a trusted
> key. These can both be configured in such a way that even root is unable to
> relax the restrictions.
>
> However, right now, there's several other straightforward ways for root to
> modify running kernel code. At the most basic level these allow root to
> reset the configuration such that modules can be loaded again, rendering
> the existing restrictions useless.
>
> This patchset adds additional restrictions to various kernel entry points
> that would otherwise make it straightforward for root to disable enforcement
> of module loading restrictions. It also provides a patch that allows the
> kernel to be configured such that module signing will be automatically
> enabled when the system is booting via UEFI Secure Boot, allowing a stronger
> guarantee of kernel integrity.

I like this approach of attaching it to the module loading logic.
Given the LSM hook for loading modules, I think I'd like to add a hook
for the secure_modules() check so that an LSM can respond "secure" as
well, if it doing module loading mediation (for example, in the case
of Chrome OS's modules-only-from-rootfs). I'll work up a patch...

-Kees

-- 
Kees Cook
Chrome OS Security
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