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

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Message-ID: <c5ecccbe-9e23-f297-8a79-2a9dd62a40fb@linux.microsoft.com>
Date:   Tue, 9 Feb 2021 10:23:37 -0800
From:   Tushar Sugandhi <tusharsu@...ux.microsoft.com>
To:     Mimi Zohar <zohar@...ux.ibm.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

Thank you Mimi for reviewing this series.

On 2021-02-08 1:10 p.m., Mimi Zohar wrote:
> 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.
> 
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.

Thanks,
Tushar

> thanks,
> 
> Mimi
>