As the ground investigation on MH17 is being heavily disturbed by the crisis in Ukraine, the United Nations is envisioning a way to enforce intelligence sharing on any information about risks to civil aircrafts.
The ICAO can currently only advise, the decision to follow its guidelines (or not) being left to countries (in the USA, the FAA is the body that makes those kind of mandatory decisions for instance).
Following the incident, airlines and industry groups have been pushing for better access to impartial, consistent intelligence about whether to fly over conflict zones.
It remains to be seen if any international agreement can truly enforce the sharing of sensitive information about airspaces. Call me doubtful.