Memory security in reconfigurable computers: Combining formal verification with monitoring

Ensuring memory access security is a challenge for reconfigurable systems with multiple cores. Previous work introduced access monitors attached to the memory subsystem to ensure that the cores adhere to pre-defined protocols when accessing memory. In this paper, we combine access monitors with a formal runtime verification technique known as proof-carrying hardware to guarantee memory security. We extend previous work on proof-carrying hardware by covering sequential circuits and demonstrate our approach with a prototype leveraging ReconOS/Zynq with an embedded ZUMA virtual FPGA overlay. Experiments show the feasibility of the approach and the capabilities of the prototype, which constitutes the first realization of proof-carrying hardware on real FPGAs. The area overheads for the virtual FPGA are measured as 2x-10x, depending on the resource type. The delay overhead is substantial with almost 100x, but this is an extremely pessimistic estimate that will be lowered once accurate timing analysis for FPGA overlays become available. Finally, reconfiguration time for the virtual FPGA is about one order of magnitude lower than for the native Zynq fabric.