Re: RFC: sign the modules at install time

From: Josh Boyer
Date: Thu Oct 18 2012 - 08:11:56 EST

On Thu, Oct 18, 2012 at 03:01:08PM +1030, Rusty Russell wrote:
> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes:
> > On Wed, Oct 17, 2012 at 3:19 PM, David Howells <dhowells@xxxxxxxxxx> 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:
> >
> > - 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.

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