linux-kernel - Re: [PATCH v4 2/6] configfs-tsm: Introduce a shared ABI for attestation reports

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Message-ID: <6513e6079a427_91c1e294e@dwillia2-xfh.jf.intel.com.notmuch>
Date:   Wed, 27 Sep 2023 01:21:27 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Thomas Fossati <thomas.fossati@...aro.org>,
        Dan Williams <dan.j.williams@...el.com>
CC:     <linux-coco@...ts.linux.dev>,
        Dionna Amalie Glaze <dionnaglaze@...gle.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Peter Gonda <pgonda@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Samuel Ortiz <sameo@...osinc.com>,
        Thomas Gleixner <tglx@...utronix.de>, <peterz@...radead.org>,
        <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v4 2/6] configfs-tsm: Introduce a shared ABI for
 attestation reports

Thomas Fossati wrote:
> Hi Dan,
> 
> > On 9/25/2023 9:17 PM, Dan Williams wrote:
> > > +++ b/include/linux/tsm.h
> > > @@ -0,0 +1,63 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > +#ifndef __TSM_H
> > > +#define __TSM_H
> > > +
> > > +#include <linux/sizes.h>
> > > +#include <linux/types.h>
> > > +#include <linux/device.h>
> > > +
> > > +#define TSM_INBLOB_MAX 64
> 
> I guess @inblob is supposed to (possibly) accommodate nonces from a
> challenger, correct?
> If so, 64 bytes may not be enough for attesters that produce
> EAT-formatted reports -- see [1], and [2].
> 
> [1] https://www.ietf.org/archive/id/draft-ietf-rats-eat-21.html#section-4.1-5
> [2] https://github.com/ietf-rats-wg/eat/pull/421/files

Hmm, but 64-bytes is the hard limit of the supported platform
implementations.

It can be expanded when/if those platforms expand the
size of the supported user data, or another configfs-tsm backend arrives
that needs that capability.