Re: [PATCH v2, RESEND 0/3] tpm: retrieve digest size of unknown algorithms from TPM

[Jarkko Sakkinen]

On Thu, Sep 27, 2018 at 08:50:14AM +0200, Roberto Sassu wrote:
> On 9/26/2018 8:03 PM, Mimi Zohar wrote:
> > On Wed, 2018-09-26 at 10:40 -0400, Mimi Zohar wrote:
> > > On Mon, 2018-09-17 at 11:38 +0200, Roberto Sassu wrote:
> > > > Resending to maintainer with correct mailing lists in CC.
> > > > 
> > > > 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.
> > > 
> > > Other than checking the digest size before copying the pcrread buffer,
> > > the patches look good.  Please add my Ack on all 3 patches.
> > > 
> > > (New address) Acked-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> > 
> > I've reviewed, and am currently running with these patches.
> > 
> > Even if the IMA changes were in a separate patch, we wouldn't be able
> > to break up the patch set anyway.  Jarkko, I'd appreciate your
> > carrying the entire patch set.
> > 
> > Roberto, a similar change needs to be made for tpm_pcr_extend.  Are
> > you planning on posting those changes as well?
> 
> Yes, I was planning to send the patch after this patch set is accepted.
> 
> Roberto

Mimi, I can carry it yes.

/Jarkko