Processor Hardware Security Vulnerabilities and their Detection by Unique Program Execution Checking

Recent discovery of security attacks in advanced processors, known as Spectre and Meltdown, has resulted in high public alertness about security of hardware. The root cause of these attacks is information leakage across covert channels that reveal secret data without any explicit information flow between the secret and the attacker. Many sources believe that such covert channels are intrinsic to highly advanced processor architectures based on speculation and out-of-order execution, suggesting that such security risks can be avoided by staying away from high-end processors. This paper, however, shows that the problem is of wider scope: we present new classes of covert channel attacks which are possible in average-complexity processors with in-order pipelining, as they are mainstream in applications ranging from Internet-of-Things to Autonomous Systems. We present a new approach as a foundation for remedy against covert channels: while all previous attacks were found by clever thinking of human attackers, this paper presents a formal method called Unique Program Execution Checking which detects and locates vulnerabilities to covert channels systematically, including those to covert channels unknown so far.