SeMPE: Secure Multi Path Execution Architecture for Removing Conditional Branch Side Channels

TL;DR

SeMPE introduces an architecture-based method to eliminate side channel vulnerabilities from secret-dependent branches by executing both paths, achieving low overheads and outperforming existing constant-time solutions.

Contribution

SeMPE presents a novel architecture support approach that removes conditional branch side channels with minimal programming effort and low performance overhead.

Findings

SeMPE incurs near-ideal execution overheads.

Outperforms FaCT-generated code by up to 18x.

Effectively eliminates branch-based side channels.

Abstract

One of the most prevalent source of side channel vulnerabilities is the secret-dependent behavior of conditional branches (SDBCB). The state-of-the-art solution relies on Constant-Time Expressions, which require high programming effort and incur high performance overheads. In this paper, we propose SeMPE, an approach that relies on architecture support to eliminate SDBCB without requiring much programming effort while incurring low performance overheads. The key idea is that when a secret-dependent branch is encountered, the SeMPE microarchitecture fetches, executes, and commits both paths of the branch, preventing the adversary from inferring secret values from the branching behavior of the program. To enable that, SeMPE relies on an architecture that is capable of safely executing both branch paths sequentially. Through microbenchmarks and an evaluation of a real-world library, we show that SeMPE incurs near ideal execution time overheads, which is the sum of the execution time of all branch paths of secret-dependent branches. SeMPE outperforms code generated by FaCT, a constant-time expression language, by up to a factor of 18x.