content_changed implementation

[rw8896]

libspdm/include/hal/library/responder/measlib.h

Line 77 in 704d565

uint8_t *content_changed,

Hi,

I have a question about content_changed implementation.
The integrator will need the knowledge about measurement logs in current L2 contents as a basis to check if there is any measurement changed. But the function didn't seem to be able to provide such information.
Is there a design/mechanism for integrators to acquire the information from libspdm?

[steven-bellock]

The Integrator needs to monitor request_attribute and the SignatureRequested bit, since content_change can only be asserted when a signature is requested. So it keeps track of measurements when SignatureRequested is not set, and does a comparison when SignatureRequested is set.

[rw8896]

Thanks and I think that works for normal scenario. But as "Any communication between Requester and Responder other than a GET_MEASUREMENTS request or response re-initializes L1/L2 computation to null .", the integrator seems not able to know if L1/L2 has been re-inited?

[steven-bellock]

Yes, that looks like it's an issue. The state of the l1/l2 transcript is stored in the spdm_context but it is currently not public. We would need to provide a public function to query the transcript state. @jyao1 does that sound good?

[rw8896]

I feel a callback function to notify L1/L2 was reset might be easier for integrators to track the measurement.
Maybe provide a callback function for transcript state change (similar to connection state callback)?

[steven-bellock]

I will draw up the two approaches and we can see which ones looks the best: callback versus querying the transcript from the spdm_context.