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1. SoK: Hardware Defenses Against Speculative Execution Attacks

   https://doi.org/10.1109/SEED51797.2021.00023  

   Hu, Guangyuan; He, Zecheng; Lee, Ruby B. (September 2021, 2021 International Symposium on Secure and Private Execution Environment Design (SEED))

   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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2. Speculative Execution Attacks and Hardware Defenses

   https://doi.org/10.1145/3474376.3487404  

   Lee, Ruby B. (November 2021, ASHES '21: Proceedings of the 5th Workshop on Attacks and Solutions in Hardware Security)

   Speculative execution attacks like Spectre and Meltdown exploit hardware performance optimization features to illegally access a secret and then leak the secret to an unauthorized recipient. Many variants of speculative execution attacks (also called transient execution attacks) have been proposed in the last few years, and new ones are constantly being discovered. While software mitigations for some attacks have been proposed, they often cause very significant performance degradation. Hardware solutions are also being proposed actively by the research community, especially as these are attacks on hardware microarchitecture. In this talk, we identify the critical steps in a speculative attack, and the root cause of successful attacks. We define the concept of "security dependencies", which should be implemented to prevent data leaks and other security breaches. We propose a taxonomy of defense strategies and show how proposed hardware defenses fall under each defense strategy. We discuss security-performance tradeoffs, which can decrease the performance overhead while still preventing security breaches. We suggest design principles for future security-aware microarchitecture. 

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3. Position Paper: Consider Hardware-enhanced Defenses for Rootkit Attacks

   https://doi.org/10.1145/3458903.3458909  

   Hu, Guangyuan; Zhang, Tianwei; Lee, Ruby B. (October 2020, HASP '20: Hardware and Architectural Support for Security and Privacy)

   Rootkits are malware that attempt to compromise the system’s functionalities while hiding their existence. Various rootkits have been proposed as well as different software defenses, but only very few hardware defenses. We position hardware-enhanced rootkit defenses as an interesting research opportunity for computer architects, especially as many new hardware defenses for speculative execution attacks are being actively considered. We first describe different techniques used by rootkits and their prime targets in the operating system. We then try to shed insights on what the main challenges are in providing a rootkit defense, and how these may be overcome. We show how a hypervisor-based defense can be implemented, and provide a full prototype implementation in an open-source cloud computing platform, OpenStack. We evaluate the performance overhead of different defense mechanisms. Finally, we point to some research opportunities for enhancing resilience to rootkit-like attacks in the hardware architecture. 

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4. Detecting Malicious Attacks Exploiting Hardware Vulnerabilities Using Performance Counters

   Li, C; Gaudiot, J-L (July 2019, 2019 IEEE Computer Society Signature Conference on Computers, Software and Applications (COMPSAC 2019))

   Over the past decades, the major objectives of computer design have been to improve performance and to reduce cost, energy consumption, and size, while security has remained a secondary concern. Meanwhile, malicious attacks have rapidly grown as the number of Internet-connected devices, ranging from personal smart embedded systems to large cloud servers, have been increasing. Traditional antivirus software cannot keep up with the increasing incidence of these attacks, especially for exploits targeting hardware design vulnerabilities. For example, as DRAM process technology scales down, it becomes easier for DRAM cells to electrically interact with each other. For instance, in Rowhammer attacks, it is possible to corrupt data in nearby rows by reading the same row in DRAM. As Rowhammer exploits a computer hardware weakness, no software patch can completely fix the problem. Similarly, there is no efficient software mitigation to the recently reported attack Spectre. The attack exploits microarchitectural design vulnerabilities to leak protected data through side channels. In general, completely fixing hardware-level vulnerabilities would require a redesign of the hardware which cannot be backported. In this paper, we demonstrate that by monitoring deviations in microarchitectural events such as cache misses, branch mispredictions from existing CPU performance counters, hardware-level attacks such as Rowhammer and Spectre can be efficiently detected during runtime with promising accuracy and reasonable performance overhead using various machine learning classifiers. 

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5. Sidecar: Leveraging Debugging Extensions in Commodity Processors to Secure Software

   https://doi.org/10.1109/ACSAC63791.2024.00053  

   Kleftogiorgos, Konstantinos; Zielinski, Patrick; Huang, Shan; Xu, Jun; Portokalidis, Georgios (December 2024, IEEE)

   The increased parallelism in modern processors has sparked interest in offloading security policy enforcement to processes or hardware operating in parallel with the main application. This approach can reduce application latency, enhance security, and improve compatibility. However, existing software solutions often incur high overheads and are susceptible to memory corruption attacks, while hardware solutions tend to be inflexible and require substantial modifications to the processor. In this paper, we present SIDECAR, a novel approach that offloads security checks to run concurrently with applications by leveraging the debugging infrastructure available in commodity processors. Specifically, we utilize softwaredriven logging (SDL) extensions in Intel and Arm processors to create secure, append-only channels between applications and security monitors. We build and evaluate a prototype of SIDECAR for the x86-64 and Aarch64 architectures. To demonstrate its utility, we adapt well-known security defenses within SIDECAR, providing control-flow integrity (CFI), shadow call stacks (SCS), and memory error checking (ASAN). Our evaluation shows that these extensions perform better on the Intel architecture. In terms of defenses, SIDECAR reduces the latency of CFI in the tested real-world applications by an average of 30%, offers enhanced security with similar overhead for SCS, and is versatile enough to support complex defenses like ASAN. Furthermore, our security monitor for CFI+SCS is 30 times more efficient compared to previous work. 

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