  Covert channels can be utilized to secretly deliver information from high
privileged processes to low privileged processes in the context of a
high-assurance computing system. In this case study, we investigate the
possibility of covert channel establishment via software caches in the context
of a framework for component-based operating systems. While component-based
operating systems offer security through the encapsulation of system service
processes, complete isolation of these processes is not reasonably feasible.
This limitation is practically demonstrated with our concept of a specific
covert timing channel based on file system caching. The stability of the covert
channel is evaluated and a methodology to disrupt the covert channel
transmission is presented. While these kinds of attacks are not limited to
high-assurance computing systems, our study practically demonstrates that even
security-focused computing systems with a minimal trusted computing base are
vulnerable for such kinds of attacks and careful design decisions are necessary
for secure operating system architectures.
