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Date:   Thu, 3 Oct 2019 14:33:13 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Mimi Zohar <zohar@linux.ibm.com>
Cc:     linux-integrity@vger.kernel.org,
        Jerry Snitselaar <jsnitsel@redhat.com>,
        James Bottomley <James.Bottomley@HansenPartnership.com>,
        Sumit Garg <sumit.garg@linaro.org>,
        Stefan Berger <stefanb@linux.vnet.ibm.com>,
        Peter Huewe <peterhuewe@gmx.de>,
        Jason Gunthorpe <jgg@ziepe.ca>, Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] tpm: Detach page allocation from tpm_buf
Message-ID: <20191003113313.GD8933@linux.intel.com>
References: <20190925134842.19305-1-jarkko.sakkinen@linux.intel.com>
 <20190926124635.GA6040@linux.intel.com>
 <20190926131227.GA6582@linux.intel.com>
 <1570020024.4999.104.camel@linux.ibm.com>
 <20191003113211.GC8933@linux.intel.com>
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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