Moats and Drawbridges: An Isolation Primitive for Reconfigurable Hardware Based Systems

Blurring the line between software and hardware, re-configurable devices strike a balance between the raw high speed of custom silicon and the post-fabrication flexibility of general-purpose processors. While this flexibility is a boon for embedded system developers, who can now rapidly prototype and deploy solutions with performance approach-ing custom designs, this results in a system development methodology where functionality is stitched together from a variety of “soft IP cores, ” often provided by multiple ven-dors with different levels of trust. Unlike traditional soft-ware where resources are managed by an operating system, soft IP cores necessarily have very fine grain control over the underlying hardware. To address this problem, the em-bedded systems community requires novel security primi-tives which address the realities of modern reconfigurable hardware. We propose an isolation primitive, moats and drawbridges, that are built around four design properties: logical isolation, interconnect traceability, secure reconfig-urable broadcast, and configuration scrubbing. Each of these is a fundamental operation with easily understood for-mal properties, yet maps cleanly and efficiently to a wide va-riety of reconfigurable devices. We carefully quantify the re-quired overheads on real FPGAs and demonstrate the utility of our methods by applying them to the practical problem of memory protection.