linux-kernel - Re: [PATCH 5/5] LSM: Define workqueue for measuring security module state

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Message-ID: <CAEjxPJ7v5Lu-vzqg0ZVh8zJ9uZ=odN3jt_5+9d9x+RydsNWK0g@mail.gmail.com>
Date:   Mon, 15 Jun 2020 09:33:38 -0400
From:   Stephen Smalley <stephen.smalley.work@...il.com>
To:     Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        Stephen Smalley <stephen.smalley@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <jmorris@...ei.org>,
        linux-integrity@...r.kernel.org,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] LSM: Define workqueue for measuring security module state

On Fri, Jun 12, 2020 at 10:42 PM Lakshmi Ramasubramanian
<nramas@...ux.microsoft.com> wrote:
>
> The data maintained by the security modules could be tampered with by
> malware. The LSM needs to periodically query the state of
> the security modules and measure the data when the state is changed.
>
> Define a workqueue for handling this periodic query and measurement.

Won't this make it difficult/impossible to predict the IMA PCR value?
Unless I missed it, you are going to end up measuring every N minutes
even if there was no change and therefore constantly be extending the
PCR.  That will break attestation or sealing against the IMA PCR.