On Thu, Oct 26, 2017 at 12:26:10AM +0200, Peter Huewe wrote:

Am 25. Oktober 2017 20:53:49 MESZ schrieb Jarkko Sakkinen [off-list ref]:

quoted

On Wed, Oct 25, 2017 at 07:17:17AM -0700, Matthew Garrett wrote:

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On Wed, Oct 25, 2017 at 6:44 AM, Jarkko Sakkinen
[off-list ref] wrote:

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I'm implementing a fix for CVE-2017-15361 that simply blacklists
vulnerable FW versions. I think this is the only responsible action

from

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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.

I proposed the following as an alternative:

* Print a message to the klog (which log level would be appropriate?).

Info?
Maybe warn, definitely not err

Since the driver does not fail usually warn would make sense but since
here even allowing to continue to use such TPM is questionable I would
use error here.

People anyway ignore klog too easily so using warn would be a mistake in
my opinion. It's like saying that nothing serious is happening here,
move along.

Do you think so?

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* Possibly sleep for few seconds. Is this a good idea?

Helps how?

Obviously to get it noticed that the system integrity is broken.

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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.

No, same terrible idea since you block the upgrade path.
Upgrade tools work from userspace via the kernel driver. 
So /dev/tpm0 is necessary.

Right! How stupid of me (my previous response to Jerry) :-) Of course you
can have special commands and talk to the TPM to do the upgrade even if
it is part of the platform and not connected to a standard bus.

I got understanding in the yesterdays unconfernce discussion that it
should be part of the firmware upgrade.

How do you do the upgrade through /dev/tpm0?

/Jarkko
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