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

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Message-ID: <38ba5889d517ee010a6bf370f8892059dd7d3bfe.camel@linux.ibm.com>
Date:   Tue, 09 Feb 2021 13:53:55 -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

On Tue, 2021-02-09 at 10:23 -0800, Tushar Sugandhi wrote:
> > 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.
> > 
> Agreed.  I wasn't sure if you wanted the support for files, or other 
> buffer measurement scenarios, except critical data.  So I started the 
> implementation with supporting just critical data.  Happy to extend it 
> to files and other buffer measurement scenarios as you suggested.
> 
> > 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().
> > 
> Agreed.  Earlier I wasn't sure if you wanted allow_dup support for all 
> the scenarios.  Now that it is clear,  I will implement it as you 
> suggested.  Thank you so much for the pointers.  Appreciate it.

There are two different solutions - per measurement rule, disabling
htable - being discussed.   Disabling htable requires miminumal
changes.  Which version are you thinking of implementing?

thanks,

Mimi