In-Reply-To: <20080809184622.GA22905@infradead.org>
References: <20080808184349.999902616@linux.vnet.ibm.com> <1218221718.4444.11.camel@localhost.localdomain> <20080809184622.GA22905@infradead.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: James Morris <jmorris@namei.org>, linux-kernel@vger.kernel.org,
       linux-security-module@vger.kernel.org,
       Randy Dunlap <randy.dunlap@oracle.com>, safford@watson.ibm.com,
       sailer@watson.ibm.com, Stephen Smalley <sds@tycho.nsa.gov>,
       serue@linux.vnet.ibm.com, Al Viro <viro@ZenIV.linux.org.uk>,
       Debora Velarde <debora@linux.vnet.ibm.com>,
       Mimi Zohar <zohar@linux.vnet.ibm.com>,
       Kenneth Goldman <kgold@watson.ibm.com>
MIME-Version: 1.0
Subject: Re: [PATCH 1/4] integrity: TPM internel kernel interface
Message-ID: <OF9A2A62B8.D4E0AE57-ON852574A2.006CEDC6-852574A2.00749DAC@us.ibm.com>
From: Mimi Zohar <zohar@us.ibm.com>
Date: Mon, 11 Aug 2008 17:13:51 -0400
Content-Type: text/plain; charset="US-ASCII"
Sender: linux-kernel-owner@vger.kernel.org
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Christoph Hellwig <hch@infradead.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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