On Mon, Jul 20, 2020 at 1:34 PM Lakshmi Ramasubramanian <nramas@xxxxxxxxxxxxxxxxxxx> wrote: > > 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 It seems like one shouldn't need to manually specify it if it is the only template that yields a useful result for the LSM_STATE function?
