linux-kernel - Re: [tpmdd-devel] [RFC] tpm2-space: add handling for global session exhaustion

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Message-ID: <20170214143829.GA28175@wind.enjellic.com>
Date:   Tue, 14 Feb 2017 08:38:29 -0600
From:   "Dr. Greg Wettstein" <gw@...usion.org>
To:     Kenneth Goldman <kgoldman@...ibm.com>
Cc:     James Bottomley <James.Bottomley@...senPartnership.com>,
        greg@...ellic.com,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        tpmdd-devel@...ts.sourceforge.net
Subject: Re: [tpmdd-devel] [RFC] tpm2-space: add handling for global session exhaustion

On Fri, Feb 10, 2017 at 04:13:05PM -0500, Kenneth Goldman wrote:

Good morning to everyone.

> James Bottomley <James.Bottomley@...senPartnership.com> wrote on 
> 02/10/2017 11:46:03 AM:
> 
> > > quote: 810 milliseconds
> > > verify signature: 635 milliseconds

For those who may be interested in this sort of thing I grabbed a few
minutes and ran these basic verification primitives against a Kaby
Lake system.

Average time for a quote is 600 milliseconds with a signature
verification clocking in at 100 milliseconds.  The latter is
consistent with what James found on his Skylake machine.

Latencies are still significant with things like container start
times.

> > Part of the way of reducing the latency is not to use the TPM for
> > things that don't require secrecy: 

> Agreed.  There are a few times one would verify a signature inside the 
> TPM,
> but they're far from mainstream:
> 
> 1 - Early in the boot cycle, when there's no crypto library.
> 
> 2 - When the crypto library doesn't support the required algorithm.
> 
> 3 - When a ticket is needed to prove to the TPM later that it verified
> the signature.

I don't think there is any doubt that running cryptographic primitives
in userspace is going to be faster then going to hardware.  Obviously
that also means there is no need for a TPM resource manager which has
been the subject of much discussion here.

The CoreOS paper makes significant reference to increased security
guarantees inherent in the use of a TPM.  Obviously whatever uses
those are will have the noted latency constraints.

We have extended our behavior measurement verifications to the
container level so we offer an explicit guarantee that a container has
not operated in a manner which is inconsistent with the intent of its
designer.  Getting the security guarantee we need requires that an
linkage to a hardware root of trust hence our concerns about hardware
latency.

Have a good day.

As always,
Dr. G.W. Wettstein, Ph.D.   Enjellic Systems Development, LLC.
4206 N. 19th Ave.           Specializing in information infra-structure
Fargo, ND  58102            development.
PH: 701-281-1686
FAX: 701-281-3949           EMAIL: greg@...ellic.com
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