Re: Fixing CVE-2017-15361

[Jerry Snitselaar]

On Wed Oct 25 17, Jarkko Sakkinen wrote:
> On Wed, Oct 25, 2017 at 07:17:17AM -0700, Matthew Garrett wrote:
> > On Wed, Oct 25, 2017 at 6:44 AM, Jarkko Sakkinen
> > <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:
> > > I'm implementing a fix for CVE-2017-15361 that simply blacklists
> > > vulnerable FW versions. I think this is the only responsible action from
> > > my side that I can do.
> >
> > I'm not sure this is ideal - do Infineon have any Linux tooling for
> > performing firmware updates, and if so will that continue working if
> > the device is blacklisted? It's also a poor user experience to have
> > systems using TPM-backed disk encryption keys suddenly rendered
> > unbootable, and making it as easy as possible for people to do an
> > upgrade and then re-seal secrets with new keys feels like the correct
> > approach.
>
> I talked today with Alexander Steffen in the KS unconference and we
> concluded that this would be a terrible idea.
>
> Alexander stated the following things about FW updates (Alexander,
> please correct me if I state something incorrectly or if you have
> something to add):
>
> * FW update can be constructed either in a way that the keys in the
>  NVRAM are not cleared or in a way that they are cleared.
> * FW update cannot be directly applied to the TPM but must come as
>  part of the firmware update from the vendor.

If that is the case, can the two of you get Intel to update the fw
for the tpm in the nuc5i5myhe (slb9665) :) ? It has needed an update for a while, due
to issues with context management. My understanding (quite likely I misunderstood)
from a recent discussion with Peter was that it was possible to update the fw.

> I proposed the following as an alternative:
>
> * Print a message to the klog (which log level would be appropriate?).
> * Possibly sleep for few seconds. Is this a good idea?
>
> While writing this email yet another alternative popped into my mind:
> what if we allow only in-kernel use but disallow the use of /dev/tpm0?
> You could still use trusted keys.
>
> Here are all the ideas that I have and I am open for better
> alternatives.
>
> /Jarkko