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

[Mimi Zohar]

Christoph Hellwig <hch@xxxxxxxxxxxxx> 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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