linux-kernel - Re: [PATCH v4 04/11] security: keys: trusted: Include TPM2 creation data

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Date:   Wed, 9 Nov 2022 16:29:26 -0800
From:   Evan Green <evgreen@...omium.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, corbet@....net,
        linux-pm@...r.kernel.org, rjw@...ysocki.net, gwendal@...omium.org,
        apronin@...omium.org, Pavel Machek <pavel@....cz>,
        Matthew Garrett <mgarrett@...ora.tech>,
        linux-integrity@...r.kernel.org, jejb@...ux.ibm.com,
        zohar@...ux.ibm.com, dlunev@...gle.com,
        Eric Biggers <ebiggers@...nel.org>,
        Ben Boeckel <me@...boeckel.net>, jarkko@...nel.org,
        David Howells <dhowells@...hat.com>,
        James Morris <jmorris@...ei.org>,
        Paul Moore <paul@...l-moore.com>,
        "Serge E. Hallyn" <serge@...lyn.com>, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v4 04/11] security: keys: trusted: Include TPM2 creation data

On Mon, Nov 7, 2022 at 12:11 PM Evan Green <evgreen@...omium.org> wrote:
>
> On Fri, Nov 4, 2022 at 11:33 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Thu, Nov 03, 2022 at 11:01:12AM -0700, Evan Green wrote:
> > > In addition to the private key and public key, the TPM2_Create
> > > command may also return creation data, a creation hash, and a creation
> > > ticket. These fields allow the TPM to attest to the contents of a
> > > specified set of PCRs at the time the trusted key was created. Encrypted
> > > hibernation will use this to ensure that PCRs settable only by the
> > > kernel were set properly at the time of creation, indicating this is an
> > > authentic hibernate key.
> > >
> > > Encode these additional parameters into the ASN.1 created to represent
> > > the key blob. The new fields are made optional so that they don't bloat
> > > key blobs which don't need them, and to ensure interoperability with
> > > old blobs.
> > >
> > > Signed-off-by: Evan Green <evgreen@...omium.org>
> >
> > There's a lot of open-coded math for the bounds checking. I didn't
> > immediately see any problems, but it'd be nice if there was a way to
> > hook a fuzzer up to this, or at least write some KUnit tests to check
> > boundary conditions explicitly.
> >
> > Reviewed-by: Kees Cook <keescook@...omium.org>
>
> Thank you! Yes, agreed about all the bounds checking. I could probably
> pull out the "check for src + 2 > end, then get_unaligned_be16()" into
> a helper function. Let me see if that makes things look better or ends
> up looking the same.

A helper function cleaned this up nicely, so I'll send that in the
next spin but not yet pick up your reviewed tag.