Re: [PATCH 1/2] tpm2: add session handle context saving and restoring to the space code
From: Jarkko Sakkinen
Date: Fri Jan 27 2017 - 01:46:12 EST
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@xxxxxxxxxxxxxxxxxxxxx>
> > 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
Right. I've also set the limit for trasient objects to three.