Abstract—Most security mechanisms proposed to date unquestioningly place trust in microprocessor hardware. This trust, however, is misplaced and dangerous because microprocessors are vulnerable to insider attacks that can catastrophically compromise security, integrity and privacy of computer systems. In this paper, we describe several methods to strengthen the fundamental assumption about trust in microprocessors. By employing practical, lightweight attack detectors within a microprocessor, we show that it is possible to protect against malicious logic embedded in microprocessor hardware. We propose and evaluate two area-efficient hardware methods — TRUSTNET and DATAWATCH — that detect attacks on microprocessor hardware by knowledgeable, malicious insiders. Our mechanisms leverage the fact that multiple components within a microprocessor (e.g., fetch, decode pipeline stage etc.) must necessarily coordinate and communicate to execute even simple instructions, and that any attack...