[PATCH 0/3] support for duplicate measurement of integrity critical data

Tushar Sugandhi tusharsu at linux.microsoft.com
Tue Feb 9 18:23:37 UTC 2021

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,
> Mimi

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