Hi Tushar,

The above Subject line should be truncated to "IMA: add policy to
measure critical data".    

On Wed, 2020-09-23 at 12:20 -0700, Tushar Sugandhi wrote:

There would be several candidate kernel components suitable for IMA
measurement. Not all of them would have support for IMA measurement.

This intro is besides the point.  The patch description should describe
what is meant by "critical data".

Also, system administrators may not want to measure data for all of
them, even when they support IMA measurement.
An IMA policy option 
specific to various kernel components is needed to measure their
respective critical data.

This policy option needs to be constrained to measure data for
specific kernel components that are specified as input values to the
policy option.

Add a new IMA policy option - "data_sources:=" to allow measuring
various critical kernel components. This policy option would enable the
system administrators to limit the measurement to the components
listed in "data_sources:=", if the components support IMA measurement.

The new policy option "data_sources:=" is different from the existing
policy option "keyrings:=". 

In case of "keyrings:=", a policy may measure all keyrings (when
"keyrings:=" option is not provided for func KEY_CHECK), or may
constrain which keyrings need to be measured (when "keyrings:=" option
is provided for func KEY_CHECK).

But unlike "keyrings:=", the entries in "data_sources:=" would have
different data format. Further, the components listed in
"data_sources:=" need to be modified to call IMA to measure their
data. Therefore, unlike "keyrings:=", IMA shouldn't measure all of the
components by default, when "data_sources:=" is not specified. Because
measuring non-vetted components just by specifying them as a policy
option value may impact the overall reliability of the system.

To address this, "data_sources:=" should be a mandatory policy option
for func=CRITICAL_DATA. This func is introduced in the 5th patch in this
series). And the compile-time vetting functionality described above is
introduced in the 6th patch in this series.

Signed-off-by: Tushar Sugandhi <redacted>

I don't understand what you mean by "non-vetted" components, nor how
measuring critical data may impact the overall reliability of the
system.

The system owner or adminstrator defines what they want to measure,
including "critical data", based on the policy rules.  They might
decide that they want to constrain which "critical data" is measured by
specifying "data_sources:=", but that decision is their perogative.  
The default should allow measuring all critical data.

 A simple example of "critical data" could be some in memory structure,
along the lines of __ro_after_init, or hash of the memory structure. 
Once the data structure is initialized, the "critical data" measurement
shouldn't change.    From the attestation server perspective, the IMA
measurement list would contain a single record unless the critical data
changes.  The attestation server doesn't need to know anything about
the initial value, just that it has changed in order to trigger some
sort alert.

thanks,

Mimi