linux-kernel - Re: [PATCH 1/4] integrity: TPM internel kernel interface

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Message-ID: <OF9A2A62B8.D4E0AE57-ON852574A2.006CEDC6-852574A2.00749DAC@us.ibm.com>
Date:	Mon, 11 Aug 2008 17:13:51 -0400
From:	Mimi Zohar <zohar@...ibm.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Randy Dunlap <randy.dunlap@...cle.com>, safford@...son.ibm.com,
	sailer@...son.ibm.com, Stephen Smalley <sds@...ho.nsa.gov>,
	serue@...ux.vnet.ibm.com, Al Viro <viro@...IV.linux.org.uk>,
	Debora Velarde <debora@...ux.vnet.ibm.com>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Kenneth Goldman <kgold@...son.ibm.com>
Subject: Re: [PATCH 1/4] integrity: TPM internel kernel interface

Christoph Hellwig <hch@...radead.org> wrote on 08/09/2008 02:46:22 PM:

> > +{
> > +   struct tpm_chip *pos;
> > +
> > +   spin_lock(&driver_lock);
> > +   list_for_each_entry(pos, &tpm_chip_list, list) {
> > +      if ((chip_num == TPM_ANY_NUM || pos->dev_num == chip_num)
> > +          && (chip_typ == TPM_ANY_TYPE)) {
> > +         spin_unlock(&driver_lock);
> > +         return pos;
> > +      }
> > +   }
> > +
> > +   spin_unlock(&driver_lock);
> 
> besides the usual coding style issues, what protects the chip from going
> away afer you dropped the lock?
> 

I assume the concern here is that between looking up the chip and actually 

using the chip, the TPM chip is disabled/deactivated.  Based on 
discussions 
with Kenneth Goldman, the TCG main specification part2: structures, 
require
that even if the TPM is disabled/deactivated, the command to extend the 
PCR 
will succeed, but the command to read the PCR will fail with an 
appropriate 
error code.

Mimi
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