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

[Jarkko Sakkinen]

On Thu, Oct 03, 2019 at 02:32:11PM +0300, Jarkko Sakkinen wrote:
> On Wed, Oct 02, 2019 at 08:40:24AM -0400, Mimi Zohar wrote:
> > 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.  At what point does this occur?
> >  On registration?  Whenever getting a random number?  Is the result
> > cached in chip->flags?
> 
> On registeration. It is just printed to klog.
> 
> > Will this delay the TPM initialization, causing IMA to go into "TPM
> > bypass mode"?
> 
> Of course it will delay the init.
> 
> As I've stated before the real fix for the bypass issue would be
> to make TPM as part of the core but this has not received much
> appeal. I think I've sent patch for this once.

It has been like that people reject a fix to a race condition and
then I get complains on adding minor latency to the init because
of the existing race. It is ridicilous, really.

/Jarkko