Hi

And apologies for late review.

On Mon, Sep 25, 2017 at 01:19:47PM +0200, Roberto Sassu wrote:

This patch set derives from a larger patch set which modifies the TPM
driver API in order to extend a PCR with multiple digests. It can be
retrieved at the URL:

https://sourceforge.net/p/tpmdd/mailman/message/35905412/

A patch set should be able to live on its own. Please remove this link.

I don't care about that patch set at this point and I'm not going to
give any distant promises.

The TPM driver currently relies on the crypto subsystem to determine the
digest size of supported TPM algorithms. In the future, TPM vendors might
implement new algorithms in their chips, and those algorithms might not
be supported by the crypto subsystem.

Usually, vendors provide patches for the new hardware, and likely
the crypto subsystem will be updated before the new algorithm is
introduced. However, old kernels might be updated later, after patches
are included in the mainline kernel. This would leave the opportunity
for attackers to misuse PCRs, as PCR banks with an unknown algorithm
are not extended.

This patch set provides a long term solution for this issue. If a TPM
algorithm is not known by the crypto subsystem, the TPM driver retrieves
the digest size from the TPM with a PCR read. All the PCR banks are
extended, even if the algorithm is not yet supported by the crypto
subsystem.

This part makes sense to me.

/Jarkko
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