SUIT: Secure Undervolting with Instruction Traps

Modern CPUs dynamically scale voltage and frequency to improve efficiency. Voltages that are too low make the CPU unreliable and, as prior work showed, result in undetected computation errors that can be exploited to compromise systems. Hence, vendors use a generous safety margin at each voltage level, avoiding erroneous computations at the cost of substantial energy overheads.
In this work, we present SUIT, a novel hardware-software co-design to reduce the safety margin substantially without compromising reliability or security. We build on the observation that not all instructions are equally affected by undervolting faults and that most faultable instructions are infre-
quent in practice. Hence, SUIT addresses infrequent faultable instructions via two separate DVFS curves, a conservative and an efficient one. For frequent faultable instructions, SUIT statically relaxes the critical path of the corresponding instructions in hardware. Consequently, the instruction is not faultable anymore on the efficient DVFS curve at the cost of performance overheads for this specific instruction. For infrequent faultable instructions, SUIT introduces a trap mechanism preventing execution on the efficient curve. With this trap mechanism, SUIT temporarily switches to the conservative DVFS curve and switches back if no faultable instruction was executed within a certain time frame. We evaluate all building blocks of SUIT, using both measurements on real hardware and simulations, showing a performance overhead of 3.79 %, and a CPU efficiency gain of 20.8 % on average on SPEC CPU2017.