linux-kernel - Re: [PATCH] tpm: Detach page allocation from tpm

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Message-Id: <1570020024.4999.104.camel@linux.ibm.com>
Date:   Wed, 02 Oct 2019 08:40:24 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-integrity@...r.kernel.org
Cc:     Jerry Snitselaar <jsnitsel@...hat.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: Detach page allocation from tpm_buf

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?

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

Mimi