linux-kernel - Re: [PATCH 0/3] support for duplicate measurement of integrity critical data

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Date:   Mon, 08 Feb 2021 16:10:29 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Tushar Sugandhi <tusharsu@...ux.microsoft.com>,
        stephen.smalley.work@...il.com, casey@...aufler-ca.com,
        agk@...hat.com, snitzer@...hat.com, gmazyland@...il.com,
        paul@...l-moore.com
Cc:     tyhicks@...ux.microsoft.com, sashal@...nel.org, jmorris@...ei.org,
        nramas@...ux.microsoft.com, linux-integrity@...r.kernel.org,
        selinux@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: [PATCH 0/3] support for duplicate measurement of integrity
 critical data

Hi Tushar,


On Mon, 2021-02-08 at 15:22 -0500, Mimi Zohar wrote:
> On Fri, 2021-01-29 at 16:45 -0800, Tushar Sugandhi wrote:
> > IMA does not measure duplicate buffer data since TPM extend is a very
> > expensive operation.  However, in some cases for integrity critical
> > data, the measurement of duplicate data is necessary to accurately
> > determine the current state of the system.  Eg, SELinux state changing
> > from 'audit', to 'enforcing', and back to 'audit' again.  In this
> > example, currently, IMA will not measure the last state change to
> > 'audit'.  This limits the ability of attestation services to accurately
> > determine the current state of the integrity critical data on the
> > system.
> > 
> > This series addresses this gap by providing the ability to measure
> > duplicate entries for integrity critical data, driven by policy.
> 
> The same reason for re-measuring buffer data is equally applicable to
> files.  In both cases, the file or the buffer isn't re-measured if it
> already exists in the htable.   Please don't limit this patch set to
> just buffer data.

Instead of making the change on a per measurement rule basis, disabling
"htable" would be the simplest way of forcing re-measurements.  All
that would be needed is a new Kconfig (e.g. CONFIG_IMA_DISABLE_HTABLE)
and the associated test in ima_add_template_entry().

thanks,

Mimi