Re: [Linux-ima-devel] [PATCH v3 0/6] Updated API for TPM 2.0 PCR extend

Mimi Zohar
2017-06-26T12:34:19Z

On Sat, 2017-06-24 at 11:03 +0200, Jarkko Sakkinen wrote:
> On Wed, Jun 21, 2017 at 04:29:35PM +0200, Roberto Sassu wrote:

> To move this forward and be more constructive here's how I see it
> should be done (along the lines, draft):
>
> int tpm_pcr_extend(u32 chip_num, int pcr_idx, unsigned int alg,
> const u8 *hash);
>
> The paramater 'alg' is crypto ID as specified by crypto subsystem.

Based on Kenneth Goldman's input, the new IMA TPM-2.0 crypto hash
agile measurement list will contain the TPM crypto hash algorithm ids
(TPM crypto-ID).

> TPM driver must have a precompiled table of mappings for crypto IDs
> and TPM algorithm IDs.

We could map the TPM crypto-IDs to the crypto subsystem IDs and then
map them back, but is that necessary?

>
> In addition it must have dynamically acquired list of TPM alg IDs.
> For those algs that static mapping does not exist it must extend
> them like we do now everything else except SHA-1 (Naynas changes).

Padding/truncating an unknown bank using SHA1 is fine, but at some
point, as Roberto pointed out to me, TPM 2.0's might not support SHA-
1.  So for the record, we're hard coding the use of SHA1 for the
unknown algorithms whether or not the TPM supports SHA1.

> There's absolutely no need to pass digest size like you do BTW as it is
> defined by the standard.

For algorithms known to the crypto subsystem, that is fine, but for
the unknown TPM crypto algorithms, we would need to somehow query the
TPM for the digest sizes to create the mapping.

Mimi

> I also except that where ever this interleaves with trusted keys there
> won't be duplicate structures and code.
>
> /Jarkko
>