As all conceptual layers in the software stack depend on the operating system (OS) to reliably provide resource-management services and isolation, it can be considered the “reliable computing base” that must be hardened for correct operation under fault models such as transient hardware faults in the memory hierarchy. In this chapter, we approach the problem of system-software hardening in three complementary scenarios. (1) We address the following research question: Where do the general reliability limits of static system-software stacks lie, if designed from scratch with reliability as a first-class design goal? In order to reduce the proverbial “attack surface” as far as possible, we harness static application knowledge from an AUTOSAR-compliant task set, and protect the whole OS kernel with AN-encoding. This static approach yields an extremely reliable software system, but is constrained to specific application domains. (2) We investigate how reliable a dynamic COTS embedded OS can become if hardened with programming-language and compiler-based fault-tolerance techniques. We show that aspect-oriented programming is an appropriate means to encapsulate generic software-implemented hardware fault tolerance mechanisms that can be application-specifically applied to a selection of OS components. (3) We examine how system-software stacks can survive even more adverse fault models like whole-system outages, using emerging persistent memory (PM) technology as a vehicle for state conservation. Our findings include that software transactional memory facilitates maintaining consistent state within PM and allows fast recovery.
