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

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Date:   Thu, 3 Oct 2019 14:32:11 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        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 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.

/Jarkko