Affiliations: Computer Science and Engineering Department Arizona
State University Phoenix, Arizona
Abstract: Covert channel is a growing concern for multilevel secure systems.
This paper addresses the covert channel issue in the scheduling steps of
precedence related set of tasks for multiprocessor environments. Existing
solution approaches for covert channel elimination, with a totally ordered set
of classes, would adopt a lower security class first
(LSF) scheduling approach. Despite providing covert channel free scheduling,
the LSF scheduler has well known performance disadvantages, e.g., increased
response time for higher security class tasks. We propose an opportunistic
scheduling (OPS) approach, which works in conjunction with LSF, but which can
minimize the performance overheads of the LSF approach. The OPS policy
identifies opportunities where a higher security class task can be executed
prior to the completion of other lower class tasks, without creating any covert
channels. This is a temporal relaxation of the overall LSF scheduling premise.
However, we demonstrate that following the guidelines of the OPS scheduler such
violations of the LSF policy cannot create any covert channels. Selection of
the opportunities for the makespan reduction is done in a way
that Multilevel security (MLS) requirements are satisfied. OPS, therefore, is
an absolute improvement over the LSF approach without any significant
performance overhead (or, security compromise). Performance benefits of the
OPS, over the LSF scheduler, is shown by simulation.
