Messages in this thread | | | Subject | Re: [PATCH v3 4/5] LSM: Define SELinux function to measure security state | From | Lakshmi Ramasubramanian <> | Date | Mon, 20 Jul 2020 10:34:06 -0700 |
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On 7/20/20 10:06 AM, Stephen Smalley wrote:
>> The above will ensure the following sequence will be measured: >> #1 State A - Measured >> #2 Change from State A to State B - Measured >> #3 Change from State B back to State A - Since the measured data is >> same as in #1, the change will be measured only if the event name is >> different between #1 and #3 > > Perhaps the timestamp / sequence number should be part of the hashed > data instead of the event name?
If the timestamp/seqno is part of the hashed data, on every call to measure IMA will add a new entry in the IMA log. This would fill up the IMA log - even when there is no change in the measured data.
To avoid that I keep the last measurement in SELinux and measure only when there is a change with the timestamp in the event name.
> I can see the appraiser wanting to know two things: > 1) The current state of the system (e.g. is it enforcing, is the > currently loaded policy the expected one?). > 2) Has the system ever been in an unexpected state (e.g. was it > temporarily switched to permissive or had an unexpected policy > loaded?)
Yes - you are right. The appraiser will have to look at the entire IMA log (and the corresponding TPM PCR data) to know the above.
Time t0 => State of the system measured Time tn => State changed and the new state measured Time tm => State changed again and the new state measured.
Say, the measurement at "Time tn" was an illegal change, the appraiser would know.
> > I applied the patch series on top of the next-integrity branch, added > measure func=LSM_STATE to ima-policy, and booted that kernel. I get > the following entries in ascii_runtime_measurements, but seemingly > missing the final field: > > 10 8a09c48af4f8a817f59b495bd82971e096e2e367 ima-ng > sha256:21c3d7b09b62b4d0b3ed15ba990f816b94808f90b76787bfae755c4b3a44cd24 > selinux-state > 10 e610908931d70990a2855ddb33c16af2d82ce56a ima-ng > sha256:c8898652afd5527ef4eaf8d85f5fee1d91fcccee34bc97f6e55b96746bedb318 > selinux-policy-hash > > Thus, I cannot verify. What am I missing? >
Looks like the template used is ima-ng which doesn't include the measured buffer. Please set template to "ima-buf" in the policy.
For example, measure func=LSM_STATE template=ima-buf
thanks, -lakshmi
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