Privileged operations in the PlanetLab virtualised environment

Virtualised systems have experienced a resurgence in popularity in recent years, whether used to support multiple OSes running on a user's desktop, provide commercial application hosting facilities, or isolate a large number of users from each other in global network testbeds. We also see an increasing level of interest in having entities within these virtualised systems interact with each other, either as peers or as helpers providing a service to clients. Very little work has been previously conducted on how such interaction between virtualised environments can take place. We introduce Proper, a service running on the PlanetLab system, that allows unprivileged entities to access privileged operations in a safe, tightly controlled manner. This paper describes our work designing and implementing Proper, including a discussion of the various architectural decisions made. We describe how implementing such a system in a traditional UNIX environment is non-trivial, and provide a number of examples of how services running on PlanetLab actually use Proper.