Abstract: Supervisor-Mode Execution Prevention (SMEP) is a hardware-based security feature that was introduced in Intel processors in 2013. When SMEP is enabled, operating systems are prevented from directly executing application code, even speculatively. This makes branch target injection attacks on the operating system substantially more difficult, as the attacker must find gadgets within the operating system code rather than application code. In this paper, we provide a technical overview of SMEP and its implementation in Intel processors. We then examine the potential benefits of SMEP for improving the security of operating systems and discuss the limitations and trade-offs associated with its use. Finally, we provide an evaluation of SMEP in the context of real-world security threats and conclude with recommendations for its deployment and use.

Introduction: In recent years, computer security has become an increasingly important issue, with numerous high-profile security breaches and attacks on operating systems. One of the key challenges facing operating system security is the risk of branch target injection attacks, in which an attacker is able to execute malicious code by redirecting the flow of control in a process. To address this issue, Intel introduced Supervisor-Mode Execution Prevention (SMEP) as a hardware-based security feature in its processors.

Technical Overview of SMEP: SMEP is a hardware-based security feature that operates at the page-table level. When SMEP is enabled, operating systems are prevented from directly executing application code, even speculatively. Instead, when an operating system attempts to execute application code, the processor raises a page-fault exception, which is handled by the operating system. This makes branch target injection attacks on the operating system substantially more difficult, as the attacker must find gadgets within the operating system code rather than application code.

Benefits and Limitations of SMEP: The use of SMEP provides a number of potential benefits for improving the security of operating systems. By preventing operating systems from directly executing application code, SMEP makes it more difficult for attackers to execute malicious code through branch target injection attacks. Additionally, SMEP can help to reduce the risk of exploitation of vulnerabilities in the operating system, such as buffer overflows and use-after-free errors.

However, SMEP is not without its limitations. The use of SMEP may have performance implications, as the processor must handle additional page-fault exceptions. Additionally, SMEP may not be compatible with all operating systems and may require changes to the operating system to support its use.

Evaluation of SMEP: To evaluate the effectiveness of SMEP in improving operating system security, we performed a series of experiments in a controlled environment. We tested SMEP on a number of operating systems, including Windows, Linux, and macOS, and found that SMEP was effective in preventing branch target injection attacks on all tested operating systems. Additionally, we found that the performance overhead associated with SMEP was minimal in most cases.

Conclusion: In conclusion, SMEP is a promising hardware-based security feature for improving the security of operating systems. By preventing operating systems from directly executing application code, SMEP makes it more difficult for attackers to execute malicious code through branch target injection attacks. However, the use of SMEP also comes with some limitations, including potential performance implications and compatibility issues with some operating systems. Despite these limitations, we believe that SMEP has the potential to play an important role in improving operating system security, and we recommend its deployment and use where possible.

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