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Subject: Re: [PATCH 5/5] LSM: Define workqueue for measuring security module
 state
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Stephen Smalley <stephen.smalley.work@gmail.com>,
        Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Cc:     Stephen Smalley <stephen.smalley@gmail.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        James Morris <jmorris@namei.org>,
        linux-integrity@vger.kernel.org,
        LSM List <linux-security-module@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Date:   Mon, 15 Jun 2020 10:59:05 -0400
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On Mon, 2020-06-15 at 09:33 -0400, Stephen Smalley wrote:
> On Fri, Jun 12, 2020 at 10:42 PM Lakshmi Ramasubramanian
> <nramas@linux.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.

Even if it attempts to add the same measurement to the list multiple
times, unless something changed, there should only be one measurement
in the list.

Mimi