Speculative execution attacks leverage the speculative and out-of-order execution features in modern computer processors to access secret data or execute code that should not be executed. Secret information can then be leaked through a covert channel. While software patches can be installed for mitigation on existing hardware, these solutions can incur big performance overhead. Hardware mitigation is being studied extensively by the computer architecture community. It has the benefit of preserving software compatibility and the potential for much smaller performance overhead than software solutions. This paper presents a systematization of the hardware defenses against speculative execution attacks that have been proposed. We show that speculative execution attacks consist of 6 critical attack steps. We propose defense strategies, each of which prevents a critical attack step from happening, thus preventing the attack from succeeding. We then summarize 20 hardware defenses and overhead-reducing features that have been proposed. We show that each defense proposed can be classified under one of our defense strategies, which also explains why it can thwart the attack from succeeding. We discuss the scope of the defenses, their performance overhead, and the security-performance trade-offs that can be made.
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SoK: Practical Foundations for Software Spectre Defenses
Spectre vulnerabilities violate our fundamental assumptions about architectural abstractions, allowing attackers to steal sensitive data despite previously state-of-the-art countermeasures. To defend against Spectre, developers of verification tools and compiler-based mitigations are forced to reason about microarchitectural details such as speculative execution. In order to aid developers with these attacks in a principled way, the research community has sought formal foundations for speculative execution upon which to rebuild provable security guarantees.This paper systematizes the community’s current knowledge about software verification and mitigation for Spectre. We study state-of-the-art software defenses, both with and without associated formal models, and use a cohesive framework to compare the security properties each defense provides. We explore a wide variety of tradeoffs in the expressiveness of formal frameworks, the complexity of defense tools, and the resulting security guarantees. As a result of our analysis, we suggest practical choices for developers of analysis and mitigation tools, and we identify several open problems in this area to guide future work on grounded software defenses.
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- Award ID(s):
- 2120696
- PAR ID:
- 10384762
- Editor(s):
- Holz, Thorsten; Ristenpart, Thomas
- Date Published:
- Journal Name:
- 2022 IEEE Symposium on Security and Privacy (SP)
- Page Range / eLocation ID:
- 666 to 680
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Transient execution attacks such as Spectre and Meltdown exploit speculative execution in modern microprocessors to leak information via cache side‐channels. Software solutions to defend against many transient execution attacks employ the
lfence serialising instruction, which does not allow instructions that come after thelfence to execute out‐of‐order with respect to instructions that come before thelfence . However, errors and Trojans in the hardware implementation oflfence can be exploited to compromise the software mitigations that uselfence . The aforementioned security gap has not been identified and addressed previously. The authors provide a formal method solution that addresses the verification oflfence hardware implementation. The authors also show how hardware Trojans can be designed to circumventlfence and demonstrate that their verification approach will flag such Trojans as well. The authors have demonstrated the efficacy of our approach using RSD, which is an open source RISC‐V based superscalar out‐of‐order processor.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/SP46214.2022.9833707
