Trusted Boot in Fedora

Simo Sorce simo at
Mon Jun 27 14:08:44 UTC 2011

On Mon, 2011-06-27 at 15:12 +0200, Miloslav Trmač wrote:
> On Mon, Jun 27, 2011 at 12:11 PM, Andrew Haley <aph at> wrote:
> > On 24/06/11 20:49, Miloslav Trmač wrote:
> >> On Fri, Jun 24, 2011 at 12:49 PM, Andrew Haley <aph at> wrote:
> >>> What I don't understand is why this feature requires a binary blob.
> >>> Surely whatever northbridge code is required can be free software,
> >>> Is this just security through obscurity?
> >>
> >> The purpose of the blob is to "measure" the system state; only the
> >> blob (and hardware reset) is allowed to restart the "measuring"
> >> process in the TPM.  For this to work securely, the blob must be
> >> signed by someone that the TPM itself trusts - otherwise an attacker
> >> could replace the blob by something that lies about the system state.
> <snip>
> > What we're saying, then, is that the TPM doesn't trust the owner of
> > the computer, but its manufacturer.  It's impossible for a user to
> > decide who they trust.
> First, the TPM (nor the CPU) really can't tell the difference between
> the owner of the computer and an author of a virus.  It's all just
> software.
> Second, every owner of a computer has to completely trust the
> manufacturer of the computer anyway - there are way too many ways the
> manufacturer can break the security of the system, e.g. backdoors in
> the CPU or motherboard, or hidden configurations of
> .
> Placing trust in the manufacturer of the hardware puts the user in no
> worse position than they were before.  And the user, of course, still
> has full control over whether to use the TPM or not, and what to use
> it for.

Trusting the manufacturer to not put bugs/backdoors is one thing.
Having to depend on the manufacturer to sign your boot sequence is
entirely different, doesn't scale and is generally not welcome.

If the manufacturer allows you to put in the TPM your own set of keys
then it's different as the user now has the power to do his own kernels
and sign them with his own key and have it verify by the TPM.

If the user trusts Fedora to do that he'd store a Fedora public key in
the TPM, if he doesn't he'll just not use TPM or re-sign kernels on
update on his own with his personal key.


Simo Sorce * Red Hat, Inc * New York

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