linux-kernel - Re: [PATCH 00/23] Crypto keys and module signing

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Date:	Mon, 04 Jun 2012 10:46:01 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Josh Boyer <jwboyer@...il.com>
Cc:	David Howells <dhowells@...hat.com>, kyle@...artin.ca,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, keyrings@...ux-nfs.org
Subject: Re: [PATCH 00/23] Crypto keys and module signing

On Thu, 31 May 2012 11:35:23 -0400, Josh Boyer <jwboyer@...il.com> wrote:
> On Sun, May 27, 2012 at 1:41 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> > On Thu, 24 May 2012 15:00:51 +0100, David Howells <dhowells@...hat.com> wrote:
> >> > > Why would you want multiple signatures?  That just complicates things.
> >> >
> >> > The code above stays pretty simple; if the signature fails, you set size
> >> > to i, and loop again.  As I said, if you know exactly how you're going
> >> > to strip the modules, you can avoid storing the stripped module and
> >> > simply append both signatures.
> >>
> >> You still haven't justified it.  One of your arguments about rejecting the ELF
> >> parsing version was that it was too big for no useful extra value that I could
> >> justify.  Supporting multiple signatures adds extra size and complexity for no
> >> obvious value.
> >
> > One loop is a lot easier to justify that the ELF-parsing mess.  And it
> > can be done in a backwards compatible way tomorrow: old kernels will
> > only check the last signature.
> >
> > I had assumed you'd rather maintain a stable strip util which you can
> > use on kernel modules than rework your module builds.  I guess not.
> 
> Could you elaborate on this part a bit?  Do you mean integrate a
> standalone strip utility in the kernel sources and maintain that for
> use during module builds?  Or am I misunderstanding and you meant
> something else?

In the kernel sources, no.  But could RH maintain such a thing?  Surely.

Whether they want to guarantee that their strip is stable on kernel
modules, or create a minimal 'kmod-strip' is up to them.

> I can see how that sounds simple and desirable from one aspect, but
> it seems somewhat odd to me to duplicate the existing (or create from
> scratch) strip utilities.

Mangling a module after it is signed is very odd, and odd things aren't
nice for security features.  That's how we got here; I'm trying to move
the oddness out of the verification path.

Cheers,
Rusty.
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