Covert channels through branch predictors: a feasibility study

Covert channels through shared processor resources provide secret communication between malicious processes. In this paper, we introduce a new mechanism for covert communication using the processor branch prediction unit. Specifically, we demonstrate how a trojan and a spy can manipulate the branch prediction tables in a way that creates high-capacity, robust and noise-resilient covert channel. We demonstrate this covert channel on a real hardware platform both in Simultaneous Multi-Threading (SMT) and single-threaded settings. We also discuss techniques for improving the channel quality and outline possible defenses to protect against this covert channel.