HoBBy: Hardening Unbalanced Branches against Control Flow Attacks on Intel SGX and AMD SEV

This paper introduces HoBBy, a compiler-based tool that hardens unbalanced branches at the instruction level, making parallel control flows indistinguishable to state-of-theart attacks that bypass the source-code level balancing. To achieve this, we propose a single-step analysis method to identify unbalanced instructions in secret-dependent branches, and implement instruction shadowing, cogging, and spiraling techniques to protect them. We evaluate HoBBy by hardening secret-dependent branches in four real-world applications, validating its resilience against three state-of-the-art attacks targeting Intel SGX and AMD SEV. HoBBy achieves a runtime overhead of 2.8% for cryptographic libraries and a binary size overhead of $\mathbf{0. 6 \%}$.