MeltdownPrime and SpectrePrime: Automatically-Synthesized Attacks Exploiting Invalidation-Based Coherence Protocols (1802.03802v1)

Abstract: The recent Meltdown and Spectre attacks highlight the importance of automated verification techniques for identifying hardware security vulnerabilities. We have developed a tool for synthesizing microarchitecture-specific programs capable of producing any user-specified hardware execution pattern of interest. Our tool takes two inputs: a formal description of (i) a microarchitecture in a domain-specific language, and (ii) a microarchitectural execution pattern of interest, e.g. a threat pattern. All programs synthesized by our tool are capable of producing the specified execution pattern on the supplied microarchitecture. We used our tool to specify a hardware execution pattern common to Flush+Reload attacks and automatically synthesized security litmus tests representative of those that have been publicly disclosed for conducting Meltdown and Spectre attacks. We also formulated a Prime+Probe threat pattern, enabling our tool to synthesize a new variant of each---MeltdownPrime and SpectrePrime. Both of these new exploits use Prime+Probe approaches to conduct the timing attack. They are both also novel in that they are 2-core attacks which leverage the cache line invalidation mechanism in modern cache coherence protocols. These are the first proposed Prime+Probe variants of Meltdown and Spectre. But more importantly, both Prime attacks exploit invalidation-based coherence protocols to achieve the same level of precision as a Flush+Reload attack. While mitigation techniques in software (e.g., barriers that prevent speculation) will likely be the same for our Prime variants as for original Spectre and Meltdown, we believe that hardware protection against them will be distinct. As a proof of concept, we implemented SpectrePrime as a C program and ran it on an Intel x86 processor, averaging about the same accuracy as Spectre over 100 runs---97.9% for Spectre and 99.95% for SpectrePrime.

• The paper introduces an automated synthesis tool that generates microarchitecture-specific security tests using formal execution patterns and HB graphs.
• The study presents MeltdownPrime and SpectrePrime, which leverage invalidation-based cache coherence to enhance exploit precision over traditional methods.
• Experimental results on Intel x86 hardware demonstrate SpectrePrime achieving 99.95% accuracy, underscoring both theoretical and practical impacts on hardware security.

Overview of MeltdownPrime and SpectrePrime: Automatically-Synthesized Attacks Exploiting Invalidation-Based Coherence Protocols

In the context of increasing concerns around hardware security vulnerabilities, the paper "MeltdownPrime and SpectrePrime: Automatically-Synthesized Attacks Exploiting Invalidation-Based Coherence Protocols" adds a significant contribution by presenting an innovative approach to synthesizing microarchitecture-specific attack programs. The authors introduce a tool capable of automatically generating security exploits by using a formal description of microarchitectural execution patterns and a specific microarchitecture. This tool's capability is demonstrated through the synthesis of Meltdown and Spectre attacks, as well as proposing new variants — MeltdownPrime and SpectrePrime.

Key Contributions

The paper's primary contribution is an automated tool designed to synthesize microarchitecture-specific security litmus tests. These tests abstract complex security exploits into simple, analyzable patterns, enabling the examination and anticipation of potential vulnerabilities. The synthesis tool utilizes relational model-finding (RMF) techniques and builds upon the Check suite's happens-before (HB) graph constructs to analyze microarchitectural execution patterns, particularly those relating to cache-based side-channel attacks.

Detailed Analysis of MeltdownPrime and SpectrePrime

The paper introduces MeltdownPrime and SpectrePrime, two novel exploits that adapt the Prime+Probe cache timing side-channel method in contrast to the original Flush+Reload approach used by Meltdown and Spectre. The key difference and novelty are that these Prime variants leverage invalidation messages within the cache coherence protocol, thus extending the scope and precision of attacks similar to their predecessors.

1. MeltdownPrime and SpectrePrime Pattern Identification: The patterns were enabled by exploiting invalidation-based coherence protocols, which hold the potential not only to observe cache activity (typical of side-channel attacks) but also to understand the subtle interplay of speculative execution with cache coherence mechanisms.
2. Experimental Validation: To validate these new attack variants, SpectrePrime was implemented as a C program and tested on Intel x86 hardware. The experiments revealed that SpectrePrime achieved a remarkable average accuracy of 99.95% compared to 97.9% of the original Spectre.

Theoretical and Practical Implications

The results of this research extend the domain of hardware security analysis and carry significant implications for both theoretical exploration and practical development:

• Theoretical Implications: This work provides a formal framework for studying microarchitectural vulnerabilities by enabling automatized synthesis of attack models. Additionally, it bridges the gap between theoretical model analysis and the practical deployment of security exploits.
• Practical Implications: While software mitigation techniques developed for Meltdown and Spectre remain applicable, the distinct nature of MeltdownPrime and SpectrePrime introduces unique challenges in developing robust hardware defenses. The key challenge lies in addressing microarchitectural vulnerabilities related to coherence protocols which were not previously a focal point.

Future Directions

The development of automatic synthesis of attack models heralds a new direction in security research, encouraging further exploration into:

• Refinement of Model Synthesis Tools: Continued improvement in the automation of exploit generation and validation processes can enhance the proactive identification and fixing of hardware vulnerabilities.
• Broadening Attack Scenarios: Extending research to include a wider range of attack patterns can improve the comprehensiveness of hardware security evaluations.

In conclusion, the paper delivers a novel perspective on utilizing automated tools for the synthesis of attack programs, opening pathways for addressing complex security vulnerabilities within microarchitectures. This pivotal work underscores not just the sophistication of developing exploits but also the urgent necessity for innovative defense mechanisms tailored to emergent hardware exploits.