This article presents a novel recursive smooth trajectory (RST) generation algorithm for application in robotics and in particular for unmanned aerial vehicles (UAVs). RST builds the trajectory recursively as a smooth polynomial path, thus a closed form trajectory satisfying any arbitrary dynamic limitation that translates into kinematic constraints (e.g., position, velocity, acceleration, etc.). Uncertainties and perturbations in the constraints are also discussed, modeled, and finally included in the calculation of the polynomial trajectory coefficients. Moreover, due to its recursive formulation, RST enables an immediate extension toward the solution of a trajectory optimization problem. In particular, it is shown that the minimum-snap piecewise polynomial trajectory can be interpreted as a special case of RST. The effectiveness of the proposed algorithm is demonstrated numerically via two illustrative scenarios. Its application to a UAV structure is also discussed to highlight the advantage of a smooth path over a piecewise one. Finally, the computational complexity and memory requirements are analyzed.

The number and complexity of attacks on computer systems are increasing. This growth necessitates proper defense mechanisms. Intrusion detection systems play an important role in detecting and disrupting attacks before they can compromise software. Multivariant execution is an intrusion detection mechanism that executes several slightly different versions, called variants, of the same program in lockstep. The variants are built to have identical behavior under normal execution conditions. However, when the variants are under attack, there are detectable differences in their execution behavior. At runtime, a monitor compares the behavior of the variants at certain synchronization points and raises an alarm when a discrepancy is detected. We present a monitoring mechanism that does not need any kernel privileges to supervise the variants. Many sources of inconsistencies, including asynchronous signals and scheduling of multithreaded or multiprocess applications, can cause divergence in behavior of variants. These divergences cause false alarms. We provide solutions to remove these false alarms. Our experiments show that the multivariant execution technique is effective in detecting and preventing code injection attacks. The empirical results demonstrate that dual-variant execution has on average 17 percent performance overhead when deployed on multicore processors.

In a Multi-Variant Execution Environment (MVEE), several slightly different versions of the same program are executed in lockstep. While this is done, a monitor compares the behavior of the versions at certain synchronization points with the aim of detecting discrepancies which may indicate attacks.As we show, the monitor can be implemented entirely in user space, eliminating the need for kernel modifications. As a result, the monitor is not a part of the trusted code base.We have built a fully functioning MVEE, named Orchestra, and evaluated its effectiveness. We obtained benchmark results on a quad-core system, using two variants which grow the stack in opposite directions. The results show that the overall penalty of simultaneous execution and monitoring of two variants on a multi-core system averages about 15% relative to unprotected conventional execution

While memory-safe and type-safe languages have been available for many years, the vast majority of software is still implemented in type-unsafe languages such as C/C++. Despite massive concerted efforts by software vendors such as Microsoft to eliminate buffer overflow vulnerabilities through automated and manual code review, they continue to be found and exploited. We present a novel approach that accepts the existence of overflow vulnerabilities and uses parallelism available through current and future multi-core architectures to detect vulnerabilities by monitoring the parallel execution of several slightly varying instances of the same application. During regular execution each instance performs equivalent computations. When an attacker attempts to inject an attack vector through a buffer overflow vulnerability, however, each instance reacts differently due to the variances we introduced into each instance. We describe our prototype implementation of such a parallelism-based buffer overflow detection system and demonstrate that it is capable of stopping buffer overflow vulnerabilities using actual exploit codes for the popular Apache Web server. The experimental results show that the runtime overhead of our parallel execution framework is less than 10% on average.

L1 data caches in high-performance processors continue to grow in set associativity. Higher associativity can significantly increase the cache energy consumption. Cache access latency can be affected as well, leading to an increase in overall energy consumption due to increased execution time. At the same time, the static energy consumption of the cache increases significantly with each new process generation. This paper proposes a new approach to reduce the overall L1 cache energy consumption using a combination of way caching and fast, speculative address generation. A 16-entry way cache storing a 3-bit way number for recently accessed L1 data cache lines is shown sufficient to significantly reduce both static and dynamic energy consumption of the L1 cache. Fast speculative address generation helps to hide the way cache access latency and is highly accurate. The L1 cache energy-delay product is reduced by 10% compared to using the way cache alone and by 37% compared to the use of multiple MRU technique.