Re: [Ksummit-discuss] [TECH TOPIC] Firmware signing

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Tue, 2015-07-28 at 10:05 -0700, Andy Lutomirski wrote:
> On Tue, Jul 28, 2015 at 9:42 AM, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
> > On Tue, 2015-07-28 at 17:18 +0100, David Howells wrote:
> >> Andy Lutomirski <luto@amacapital.net> wrote:
> >>
> >> > Agreed.  See about.  I don't think the concept of trust should be as
> >> > simple as "we trust" or "we don't trust" -- we should trust certain
> >> > vendors for certain purposes only.
> >>
> >> How do you deal with a big vendor, like Intel, that makes lots of different
> >> bits for lots of different purposes?
> >
> > I don't understand what you think the problem is?  What's not clear
> > about "we have to trust the vendor".  If they choose to use a single key
> > for multiple drivers, it's no more or less a problem than if they choose
> > multiple keys, one for each driver.
> >
> > I think the trust we're investing is in the provenance of the blob, not
> > the blob itself, so the firmware can't be substituted with a malicious
> > version by an outside entity.  If we don't trust the firmware vendor,
> > then all bets are off and the provenance chain is pretty meaningless.
> 
> I think we disagree on the scope of the trust.

We do?

>   I trust the USB widget
> vendor to provide firmware for the USB widget.  I might as well trust
> them to sign the firmware itself and to provide new signed blobs by
> any means (web, email, shoved in a directory, whatever).  I have no
> choice anyway, since they provided the device in the first place and
> they could have burnt anything they wanted into it.

You think I'd trust a USB vendor signature on my enterprise disk
firmware? ... how did I give that impression?

The signature gives provenance, but we still have to verify that the
attested origin is allowed to update the given object.

> This does not mean that their key should be acceptable for kexec
> images, modules, GPU firmware, firmware for different vendors' USB
> sticks, firmware for my hard disk, etc.  In fact I flat out distrust
> them if they ever try to provide such blobs.

Um, I do believe we agree here.

James

> --Andy
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