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Networks in many safety-critical systems like avionics, automotive, and industrial plants have strict end-to-end delay requirements to be met for correct system operation. Existing software-defined real-time networks do not support data plane programmability provided by recent protocol-independent switch architectures such as P4. Our research enables time-aware flow forwarding in P4-enabled software-defined time-critical networks. In this paper, we introduce time-aware flow scheduling for P4-enabled SDN architectures. We study two scheduling policies: the first one prioritizes flows based on slack (i.e., how much time is left to reach the destination), and the second one uses finish time as a priority metric, which is determined from its data rate requirements. Both approaches were implemented and tested in the P4 software stack. We find that the slack-based forwarding scheme performs better in retaining real-time requirements. Our publicly released scheduler implementations will assist network engineers in adapting programmable switches to safety-critical applications that demand precise timing guarantees. 

Modern real-time systems face increasing vulnerabilities to cyber-attacks, particularly those that use multi-core chips, where safety-critical and non-safety-critical tasks execute concurrently. Existing solutions for multicore systems often lack either determinism or cost-efficiency. This paper introduces an offline analysis technique that computes all feasible schedules for real-time tasks running on multi-core platforms. Our proposed technique isolates compromised tasks while ensuring a fail-operational system and supports low-cost, reconfigurable scheduling. The analytical models presented in this paper guarantee the hard real-time constraints of safety-critical tasks while allowing bounded deadline misses for some non-safety-critical tasks during an attack to enhance security. We name our scheme RESCUE. We conduct a comprehensive design-space exploration and evaluate its real-world efficacy using a UAV autopilot system case study deployed on a quad-core platform (Raspberry Pi). Results show that the proposed scheme introduces minimal recovery overhead, measured in microseconds on a Raspberry Pi, and achieves 100% coverage in reconfiguration responses to compromised tasks in synthetic test cases. 

Deep neural networks (DNNs) are increasingly used in time-critical, learning-enabled cyber-physical applications such as autonomous driving and robotics. Despite the growing use of various deep learning models, protecting DNN inference from adversarial threats while preserving model privacy and confidentiality remains a key concern for resource and timing-constrained autonomous cyber-physical systems. One potential solution, primarily used in general-purpose systems, is the execution of the DNN workloads withintrusted enclavesavailable on current off-the-shelf processors. However, ensuring temporal guarantees when running DNN inference within these enclaves poses significant challenges in real-time applications due to(a)the large computational and memory demands of DNN models and(b)the overhead introduced by frequent context switches between “normal” and “trusted” execution modes. This paper introduces new time-aware schemes for dynamic (EDF) and fixed-priority (RM) schedulers to preserve the confidentiality of DNN tasks by running them inside trusted enclaves. We first propose a technique thatsliceseach DNN layer and runs them sequentially in the enclave. However, due to the extra context switch overheads of individual layer slices, we further introduce a novellayer fusiontechnique. Layer fusion improves real-time guarantees by grouping multiple layers of DNN workload from multiple tasks, thus allowing them to fit and run concurrently within the enclaves while maintaining timing constraints. We implemented and tested our ideas on the Raspberry Pi platform running a DNN-enabled trusted operating system (OP-TEE with DarkNet-TZ) and three DNN architectures (AlexNet-squeezed, Tiny Darknet, YOLOv3-tiny). Compared to the layer-wise partitioning approach, layer fusion can(a)schedule up to 3x more tasksets for EDF and 5x for RM and(b)reduce context switches by up to 11.12x for EDF and by up to 11.06x for RM. 

Deep Neural Networks (DNNs) are becoming common in "learning-enabled" time-critical applications such as autonomous driving and robotics. One approach to protect DNN inference from adversarial actions and preserve model privacy/confidentiality is to execute them within trusted enclaves available in modern processors. However, running DNN inference inside limited-capacity enclaves while ensuring timing guarantees is challenging due to (a) large size of DNN workloads and (b) extra switching between "normal" and "trusted" execution modes. This paper introduces new time-aware scheduling schemes - DeepTrust^RT - to securely execute deep neural inferences for learning-enabled real-time systems. We first propose a variant of EDF (called DeepTrust^RT-LW) that slices each DNN layer and runs them sequentially in the enclave. However, due to extra context switch overheads of individual layer slices, we further introduce a novel layer fusion technique (named DeepTrust^RT-FUSION). Our proposed scheme provides hard real-time guarantees by fusing multiple layers of DNN workload from multiple tasks; thus allowing them to fit and run concurrently within the enclaves while maintaining real-time guarantees. We implemented and tested DeepTrust^RT ideas on the Raspberry Pi platform running OP-TEE+DarkNet-TZ DNN APIs and three DNN workloads (AlexNet-squeezed, Tiny Darknet, YOLOv3-tiny). Compared to the layer-wise partitioning approach (DeepTrust^RT-LW), DeepTrust^RT-FUSION can schedule up to 3x more tasksets and reduce context switches by up to 11.12x. We further demonstrate the efficacy of DeepTrust^RT using a flight controller (ArduPilot) case study and find that DeepTrust^RT-FUSION retains real-time guarantees where DeepTrust^RT-LW becomes unschedulable. 

Security is an increasing concern for real-time systems (RTS). Over the last decade or so, researchers have demonstrated attacks and defenses aimed at such systems. In this paper, we identify, classify and measure the effectiveness of the security research in this domain. We provide a high-level summary [identification] and a taxonomy [classification] of this existing body of work. Furthermore, we carry out an in-depth analysis [measurement] of scheduler-based security techniques — the most common class of real-time security mechanisms. For this purpose, we developed a common metric, “attacker’s burden”, used to measure the effectiveness of (existing as well as future) scheduler-based real-time security measures. 

System auditing is an essential tool for detecting malicious events and conducting forensic analysis. Although used extensively on general-purpose systems, auditing frameworks have not been designed with consideration for the unique constraints and properties of Real-Time Systems (RTS). System auditing could provide tremendous benefits for security-critical RTS. However, a naive deployment of auditing on RTS could violate the temporal requirements of the system while also rendering auditing incomplete and ineffectual. To ensure effective auditing that meets the computational needs of recording complete audit information while adhering to the temporal requirements of the RTS, it is essential to carefully integrate auditing into the real-time (RT) schedule. This work adapts the Linux Audit framework for use in RT Linux by leveraging the common properties of such systems, such as special purpose and predictability.Ellipsis, an efficient system for auditing RTS, is devised that learns the expected benign behaviors of the system and generates succinct descriptions of the expected activity. Evaluations using varied RT applications show thatEllipsisreduces the volume of audit records generated during benign activity by up to 97.55% while recording detailed logs for suspicious activities. Empirical analyses establish that the auditing infrastructure adheres to the properties of predictability and isolation that are important to RTS. Furthermore, the schedulability of RT tasksets under audit is comprehensively analyzed to enable the safe integration of auditing in RT task schedules.