linux-kernel - Re: [PATCH 1/2] tpm2: add session handle context saving and restoring to the space code

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Date:   Fri, 27 Jan 2017 08:45:48 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     tpmdd-devel@...ts.sourceforge.net,
        open list <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/2] tpm2: add session handle context saving and
 restoring to the space code

On Thu, Jan 26, 2017 at 07:18:49AM -0800, James Bottomley wrote:
> On Thu, 2017-01-26 at 14:51 +0200, Jarkko Sakkinen wrote:
> > On Mon, Jan 23, 2017 at 09:37:11PM -0800, James Bottomley wrote:
> > > sessions are different from transient objects in that their handles
> > > may not be virtualized (because they're used for some hmac
> > > calculations).  Additionally when a session is context saved, a
> > > vestigial memory remains in the TPM and if it is also flushed, that
> > > will be lost and the session context will refuse to load next time, 
> > > so the code is updated to flush only transient objects after a 
> > > context save.  Add a separate array (chip->session_tbl) to save and 
> > > restore sessions by handle.  Use the failure of a context save or 
> > > load to signal that the session has been flushed from the TPM and 
> > > we can remove its memory from chip->session_tbl.
> > > 
> > > Sessions are also isolated during each instance of a tpm space. 
> > >  This means that spaces shouldn't be able to see each other's 
> > > sessions and is enforced by ensuring that a space user may only 
> > > refer to sessions handles that are present in their own chip
> > > ->session_tbl.  Finally when a space is closed, all the sessions 
> > > belonging to it should be flushed so the handles may be re-used by
> > > other spaces.
> > > 
> > > Signed-off-by: James Bottomley <
> > > James.Bottomley@...senPartnership.com>
> > 
> > I'm wondering if you ever need more than two sessions at once? If we
> > would limit the number of sessions to that you could probably 
> > simplify a lot.
> 
> Three seems to be the agreed maximum: hmac authority, parameter
> encryption and command audit.
> 
> I'll fix up the rest
> 
> James

Right. I've also set the limit for trasient objects to three.

/Jarkko