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Exorcising Spectres with Secure Compilers (1910.08607v4)

Published 18 Oct 2019 in cs.PL

Abstract: Attackers can access sensitive information of programs by exploiting the side-effects of speculatively-executed instructions using Spectre attacks. To mitigate theses attacks, popular compilers deployed a wide range of countermeasures. The security of these countermeasures, however, has not been ascertained: while some of them are believed to be secure, others are known to be insecure and result in vulnerable programs. To reason about the security guarantees of these compiler-inserted countermeasures, this paper presents a framework comprising several secure compilation criteria characterizing when compilers produce code resistant against Spectre attacks. With this framework, we perform a comprehensive security analysis of compiler-level countermeasures against Spectre attacks implemented in major compilers. This work provides sound foundations to formally reason about the security of compiler-level countermeasures against Spectre attacks as well as the first proofs of security and insecurity of said countermeasures.

Citations (37)

Summary

  • The paper introduces a novel secure compilation framework that formalizes countermeasures to mitigate Spectre v1 vulnerabilities.
  • It defines a speculative safety property using taint-tracking to reliably reason about and prevent speculative execution leaks.
  • The study provides formal security proofs for defenses such as lfence insertion and strong speculative load hardening, guiding future compiler designs.

An Overview of Secure Compilers Against Spectre Attacks

The paper "Exorcising Spectres with Secure Compilers" by Marco Patrignani and Marco Guarnieri provides a detailed examination of compiler defenses against the Spectre vulnerabilities. It aims to formalize robust criteria for compilers that defend against Spectre attacks, utilizing secure compilation principles to ensure that compiled programs do not leak information through speculative execution. The authors develop rigorous definitions and proof techniques to evaluate and ensure the security of various compiler countermeasures, focusing on Spectre Variant 1 (Spectre v1).

Key Contributions

  1. Secure Compilation Framework: The authors introduce a novel secure compilation framework tailored to account for speculative execution attacks, specifically focusing on Spectre v1. Within this framework, they establish conditions under which a compiler produces code that withstands speculative execution attacks.
  2. Speculative Safety Property (): The paper proposes a speculative safety () property that represents a class of safety properties soundly over-approximating speculative non-interference (cr:sni). By leveraging taint-tracking mechanisms to express this property, it enables reasoning about Spectre-style leaks using single traces.
  3. Compiler Criteria for Secure Speculation: Two distinct secure compilation criteria are proposed:
    • Robust Speculative Safety Preservation (): Ensures preservation of the speculative safety property through compiled programs.
    • Robust Speculative Non-Interference Preservation (): Guarantees that compilers preserve speculative non-interference, ensuring that the compiled program does not leak sensitive data.
  4. Formal Analysis of Existing Countermeasures: A comprehensive evaluation of existing compiler-based countermeasures, including speculative fencing (such as lfence instructions) and speculative load hardening (SLH), is carried out. The analysis highlights the strengths and weaknesses of defenses deployed in common compilers like Microsoft Visual C++ (MSVC), Intel C++ Compiler (ICC), and Clang.
  5. Security Proofs for Compiler Countermeasures: The authors provide formally verified security proofs for the countermeasures that are found to be effective, particularly ICC's lfence insertion and a variant of SLH, which they term “strong SLH.” These proofs demonstrate the absence of speculative leaks and show that these mechanisms satisfy robust speculative safety.

Implications and Future Directions

The research underlines the necessity of formal verification in the development of compiler defenses against microarchitectural attacks like Spectre. By introducing trace-based reasoning to verify security properties, the authors lay the groundwork for constructing proofs that consider both speculative and non-speculative program behaviors.

The implications are twofold:

  • Theoretical: The paper contributes to the theory of secure compilation by illustrating that the preservation of simple safety properties, such as , can imply more complex hyperproperties like cr:sni.
  • Practical: It provides practical tools and insights for compiler designers to evaluate and improve upon existing security mechanisms. As speculative execution continues to evolve in hardware architectures, these formal methods can adapt to assess emerging vulnerabilities.

While the paper primarily addresses Spectre v1, the authors suggest that their framework can be extended to cover a broader range of speculative execution attacks, proposing enhancements to the speculative semantics and trace models to capture different variants like Spectre-RSB and Spectre-BTB.

Conclusion

Patrignani and Guarnieri's work provides a critical step forward in understanding and ensuring the security of compiler-based countermeasures against speculative execution attacks. Their formal methods form a basis for not only evaluating current defenses but also guiding future advancements in secure compilation against a persistent class of vulnerabilities in modern computing architectures.

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