Re: [PATCH] tpm: Detach page allocation from tpm_buf

[Mimi Zohar]

On Thu, 2019-09-26 at 16:12 +0300, Jarkko Sakkinen wrote:
> On Thu, Sep 26, 2019 at 03:46:35PM +0300, Jarkko Sakkinen wrote:
> > On Wed, Sep 25, 2019 at 04:48:41PM +0300, Jarkko Sakkinen wrote:
> > > -		tpm_buf_reset(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_GET_RANDOM);
> > > +		tpm_buf_reset(&buf, data_ptr, PAGE_SIZE,
> > > +			      TPM2_ST_NO_SESSIONS, TPM2_CC_PCR_EXTEND);
> > 
> > Oops.
> 
> Maybe we could use random as the probe for TPM version since we anyway
> send a TPM command as a probe for TPM version:
> 
> 1. Try TPM2 get random.
> 2. If fail, try TPM1 get random.
> 3. Output random number to klog.
> 
> Something like 8 bytes would be sufficient. This would make sure that
> no new change breaks tpm_get_random() and also this would give some
> feedback that TPM is at least somewhat working.

That involves sending 2 TPM commands. ÂAt what point does this occur?
ÂOn registration? ÂWhenever getting a random number? ÂIs the result
cached in chip->flags?

Will this delay the TPM initialization, causing IMA to go into "TPM
bypass mode"?

Mimi