linux-kernel - Re: RFC: sign the modules at install time

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Message-ID: <20121018121154.GE2934@hansolo.jdub.homelinux.org>
Date:	Thu, 18 Oct 2012 08:11:54 -0400
From:	Josh Boyer <jwboyer@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	David Miller <davem@...emloft.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	pjones@...hat.com
Subject: Re: RFC: sign the modules at install time

On Thu, Oct 18, 2012 at 03:01:08PM +1030, Rusty Russell wrote:
> Linus Torvalds <torvalds@...ux-foundation.org> writes:
> > On Wed, Oct 17, 2012 at 3:19 PM, David Howells <dhowells@...hat.com> wrote:
> >>
> >> It's probably even better to just get rid of all the automatic module signing
> >> stuff completely and leave the sign-file script for the builder to use
> >> manually.  The module verification code will still be present.
> >
> > That's just disgusting crazy talk.
> >
> > Christ, David, get a grip on yourself. You seem to dismiss the "people
> > want to build their own kernel" people entirely.
> >
> > One of the main sane use-cases for module signing is:
> >
> >  - CONFIG_CHECK_SIGNATURE=y
> >  - randomly generated one-time key
> >  - "make modules_install; make install"
> >  - "make clean" to get rid of the keys.
> >  - reboot.
> >
> > and now you have a custom kernel that has the convenience of modules,
> > yet is basically as safe as a non-modular build. The above makes it
> > much harder for any kind of root-kit module to be loaded, and
> > basically entirely avoids one fundamental security scare of modules.
> 
> If you only want this, we could SHA all the built modules, put that in
> the kernel, and verify the module being loaded matches one of them.
> 
> Sure, it means a bit of trickery to get the module sums into the
> bzImage, but the rest is trivial.

It also excludes out-of-tree drivers.  I wouldn't personally shed a tear
for them, but it eliminates a use-case that people could have if we just
stuck to the signed module approach.

I'd prefer if we just cleaned up what we already have.

josh
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