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A tale of two worlds: Assessing the vulnerability of enclave shielding runtimes

This repository contains the source code accompanying our CCS'19 paper which methodologically analyzes interface sanitization vulnerabilities for 8 different enclave shielding runtimes across the ABI and API tiers.

Jo Van Bulck, David Oswald, Eduard Marin, Abdulla Aldoseri, Flavio D. Garcia, Frank Piessens. A Tale of Two Worlds: Assessing the Vulnerability of Enclave Shielding Runtimes. In Proceedings of the 26th ACM Conference on Computer and Communications Security (CCS'19).

Abstract

This paper analyzes the vulnerability space arising in Trusted Execution Environments (TEEs) when interfacing a trusted enclave application with untrusted, potentially malicious code. Considerable research and industry effort has gone into developing TEE runtime libraries with the purpose of transparently shielding enclave application code from an adversarial environment. However, our analysis reveals that shielding requirements are generally not well-understood in real-world TEE runtime implementations. We expose several sanitization vulnerabilities at the level of the Application Binary Interface (ABI) and the Application Programming Interface (API) that can lead to exploitable memory safety and side-channel vulnerabilities in the compiled enclave. Mitigation of these vulnerabilities is not as simple as ensuring that pointers are outside enclave memory. In fact, we demonstrate that state-of-the-art mitigation techniques such as Intel’s edger8r, Microsoft’s "deep copy marshalling", or even memory-safe languages like Rust fail to fully eliminate this attack surface. Our analysis reveals 35 enclave interface sanitization vulnerabilities in 8 major open-source shielding frameworks for Intel SGX, RISC-V, and Sancus TEEs. We practically exploit these vulnerabilities in several attack scenarios to leak secret keys from the enclave or enable remote code reuse. We have responsibly disclosed our findings, leading to 5 designated CVE records and numerous security patches in the vulnerable open-source projects, including the Intel SGX-SDK, Microsoft Open Enclave, Google Asylo, and the Rust compiler.

Enclave runtime vulnerability assessment and comparison to related work on OSs and TEEs. Symbols indicate whether a vulnerability was successfully exploited (star); acknowledged but without proof-of-concept (filled bullet); or not found to apply (empty bullet). Half-filled symbols indicate that improper sanitization only leads to side-channel leakage.

Source code overview

We provide proof-of-concept exploits for the selected vulnerabilties marked with a star * in the above table. The code is organized with a subdirectory for each enclave runtime. Our attacker code is provided as patches to the untrusted runtime component. As the reported vulnerabilities have now been patched, we provide git submodules pointing to the vulnerable trusted runtime versions.

License

See the corresponding licenses of the various open-source projects we studied. Our attacker code extensions are released as free software, licensed under GPLv3.