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At least 19 recordsLinked to original sources

arXiv2007

Virtualization: A double-edged sword

Virtualization became recently a hot topic once again, after being dormant for more than twenty years. In the meantime, it has been almost forgotten, that virtual machines are not so perfect isolating environments as it seems, when looking at the principles. These lessons were already learnt earlier when the first virtualized systems have been exposed to real life usage. Contemporary virtualization software enables instant creation and destruction of virtual machines on a host, live migration from one host to another, execution history manipulation, etc. These features are very useful in practice, but also causing headaches among security specialists, especially in current hostile network environments. In the present contribution we discuss the principles, potential benefits and risks of virtualization in a deja vu perspective, related to previous experiences with virtualization in the mainframe era.

cs.OS↗

arXiv2007

A Survey of Unix Init Schemes

In most modern operating systems, init (as in "initialization") is the program launched by the kernel at boot time. It runs as a daemon and typically has PID 1. Init is responsible for spawning all other processes and scavenging zombies. It is also responsible for reboot and shutdown operations. This document describes existing solutions that implement the init process and/or init scripts in Unix-like systems. These solutions range from the legacy and still-in-use BSD and SystemV schemes, to recent and promising schemes from Ubuntu, Apple, Sun and independent developers. Our goal is to highlight their focus and compare their sets of features.

cs.OS↗

arXiv2007

Java Components Vulnerabilities - An Experimental Classification Targeted at the OSGi Platform

The OSGi Platform finds a growing interest in two different applications domains: embedded systems, and applications servers. However, the security properties of this platform are hardly studied, which is likely to hinder its use in production systems. This is all the more important that the dynamic aspect of OSGi-based applications, that can be extended at runtime, make them vulnerable to malicious code injection. We therefore perform a systematic audit of the OSGi platform so as to build a vulnerability catalog that intends to reference OSGi Vulnerabilities originating in the Core Specification, and in behaviors related to the use of the Java language. Standard Services are not considered. To support this audit, a Semi-formal Vulnerability Pattern is defined, that enables to uniquely characterize fundamental properties for each vulnerability, to include verbose description in the pattern, to reference known security protections, and to track the implementation status of the proof-of-concept OSGi Bundles that exploit the vulnerability. Based on the analysis of the catalog, a robust OSGi Platform is built, and recommendations are made to enhance the OSGi Specifications.

cs.CR↗

arXiv2007

Practical Multiwriter Lock-Free Queues for "Hard Real-Time" Systems without CAS

FIFO queues with a single reader and writer can be insufficient for "hard real-time" systems where interrupt handlers require wait-free guarantees when writing to message queues. We present an algorithm which elegantly and practically solves this problem on small processors that are often found in embedded systems. The algorithm does not require special CPU instructions (such as atomic CAS), and therefore is more robust than many existing methods that suffer the ABA problem associated with swing pointers. The algorithm gives "first-in, almost first-out" guarantees under pathological interrupt conditions, which manifests as arbitrary "shoving" among nearly-simultaneous arrivals at the end of the queue.

cs.OS↗

arXiv2007

OS Debugging Method Using a Lightweight Virtual Machine Monitor

Demands for implementing original OSs that can achieve high I/O performance on PC/AT compatible hardware have recently been increasing, but conventional OS debugging environments have not been able to simultaneously assure their stability, be easily customized to new OSs and new I/O devices, and assure efficient execution of I/O operations. We therefore developed a novel OS debugging method using a lightweight virtual machine. We evaluated this debugging method experimentally and confirmed that it can transfer data about 5.4 times as fast as the conventional virtual machine monitor.

cs.OS↗

arXiv2007

RTK-Spec TRON: A Simulation Model of an ITRON Based RTOS Kernel in SystemC

This paper presents the methodology and the modeling constructs we have developed to capture the real time aspects of RTOS simulation models in a System Level Design Language (SLDL) like SystemC. We describe these constructs and show how they are used to build a simulation model of an RTOS kernel targeting the $μ$-ITRON OS specification standard.

cs.OS↗

arXiv2008

Power-Aware Real-Time Scheduling upon Identical Multiprocessor Platforms

In this paper, we address the power-aware scheduling of sporadic constrained-deadline hard real-time tasks using dynamic voltage scaling upon multiprocessor platforms. We propose two distinct algorithms. Our first algorithm is an off-line speed determination mechanism which provides an identical speed for each processor. That speed guarantees that all deadlines are met if the jobs are scheduled using EDF. The second algorithm is an on-line and adaptive speed adjustment mechanism which reduces the energy consumption while the system is running.

cs.OS↗

arXiv2008

Exact Feasibility Tests for Real-Time Scheduling of Periodic Tasks upon Multiprocessor Platforms

In this paper we study the global scheduling of periodic task systems upon multiprocessor platforms. We first show two very general properties which are well-known for uniprocessor platforms and which remain for multiprocessor platforms: (i) under few and not so restrictive assumptions, we show that feasible schedules of periodic task systems are periodic from some point with a period equal to the least common multiple of task periods and (ii) for the specific case of synchronous periodic task systems, we show that feasible schedules repeat from the origin. We then present our main result: we characterize, for task-level fixed-priority schedulers and for asynchronous constrained or arbitrary deadline periodic task models, upper bounds of the first time instant where the schedule repeats. We show that job-level fixed-priority schedulers are predictable upon unrelated multiprocessor platforms. For task-level fixed-priority schedulers, based on the upper bounds and the predictability property, we provide for asynchronous constrained or arbitrary deadline periodic task sets, exact feasibility tests. Finally, for the job-level fixed-priority EDF scheduler, for which such an upper bound remains unknown, we provide an exact feasibility test as well.

cs.OS↗

arXiv2008

A Type System for Data-Flow Integrity on Windows Vista

The Windows Vista operating system implements an interesting model of multi-level integrity. We observe that in this model, trusted code can be blamed for any information-flow attack; thus, it is possible to eliminate such attacks by static analysis of trusted code. We formalize this model by designing a type system that can efficiently enforce data-flow integrity on Windows Vista. Typechecking guarantees that objects whose contents are statically trusted never contain untrusted values, regardless of what untrusted code runs in the environment. Some of Windows Vista's runtime access checks are necessary for soundness; others are redundant and can be optimized away.

cs.CR↗

arXiv2008

Performance Evaluation of Multiple TCP connections in iSCSI

Scaling data storage is a significant concern in enterprise systems and Storage Area Networks (SANs) are deployed as a means to scale enterprise storage. SANs based on Fibre Channel have been used extensively in the last decade while iSCSI is fast becoming a serious contender due to its reduced costs and unified infrastructure. This work examines the performance of iSCSI with multiple TCP connections. Multiple TCP connections are often used to realize higher bandwidth but there may be no fairness in how bandwidth is distributed. We propose a mechanism to share congestion information across multiple flows in ``Fair-TCP'' for improved performance. Our results show that Fair-TCP significantly improves the performance for I/O intensive workloads.

cs.NI↗

arXiv2008

Discrete Frequency Selection of Frame-Based Stochastic Real-Time Tasks

Energy-efficient real-time task scheduling has been actively explored in the past decade. Different from the past work, this paper considers schedulability conditions for stochastic real-time tasks. A schedulability condition is first presented for frame-based stochastic real-time tasks, and several algorithms are also examined to check the schedulability of a given strategy. An approach is then proposed based on the schedulability condition to adapt a continuous-speed-based method to a discrete-speed system. The approach is able to stay as close as possible to the continuous-speed-based method, but still guaranteeing the schedulability. It is shown by simulations that the energy saving can be more than 20% for some system configurations

cs.OS↗

arXiv2008

(m,k)-firm constraints and DBP scheduling: impact of the initial k-sequence and exact schedulability test

In this paper we study the scheduling of (m,k)-firm synchronous periodic task systems using the Distance Based Priority (DBP) scheduler. We first show three phenomena: (i) choosing, for each task, the initial k-sequence 1^k is not optimal, (ii) we can even start the scheduling from a (fictive) error state (in regard to the initial k-sequence) and (iii) the period of feasible DBP-schedules is not necessarily the task hyper-period. We then show that any feasible DBP-schedule is periodic and we upper-bound the length of that period. Lastly, based on our periodicity result we provide an exact schedulability test.

cs.OS↗

arXiv2008

Integrating Job Parallelism in Real-Time Scheduling Theory

We investigate the global scheduling of sporadic, implicit deadline, real-time task systems on multiprocessor platforms. We provide a task model which integrates job parallelism. We prove that the time-complexity of the feasibility problem of these systems is linear relatively to the number of (sporadic) tasks for a fixed number of processors. We propose a scheduling algorithm theoretically optimal (i.e., preemptions and migrations neglected). Moreover, we provide an exact feasibility utilization bound. Lastly, we propose a technique to limit the number of migrations and preemptions.

cs.OS↗

arXiv2008

Telex: Principled System Support for Write-Sharing in Collaborative Applications

The Telex system is designed for sharing mutable data in a distributed environment, particularly for collaborative applications. Users operate on their local, persistent replica of shared documents; they can work disconnected and suffer no network latency. The Telex approach to detect and correct conflicts is application independent, based on an action-constraint graph (ACG) that summarises the concurrency semantics of applications. The ACG is stored efficiently in a multilog structure that eliminates contention and is optimised for locality. Telex supports multiple applications and multi-document updates. The Telex system clearly separates system logic (which includes replication, views, undo, security, consistency, conflicts, and commitment) from application logic. An example application is a shared calendar for managing multi-user meetings; the system detects meeting conflicts and resolves them consistently.

cs.OS↗

arXiv2008

Control-theoretic dynamic voltage scaling for embedded controllers

For microprocessors used in real-time embedded systems, minimizing power consumption is difficult due to the timing constraints. Dynamic voltage scaling (DVS) has been incorporated into modern microprocessors as a promising technique for exploring the trade-off between energy consumption and system performance. However, it remains a challenge to realize the potential of DVS in unpredictable environments where the system workload cannot be accurately known. Addressing system-level power-aware design for DVS-enabled embedded controllers, this paper establishes an analytical model for the DVS system that encompasses multiple real-time control tasks. From this model, a feedback control based approach to power management is developed to reduce dynamic power consumption while achieving good application performance. With this approach, the unpredictability and variability of task execution times can be attacked. Thanks to the use of feedback control theory, predictable performance of the DVS system is achieved, which is favorable to real-time applications. Extensive simulations are conducted to evaluate the performance of the proposed approach.

cs.OS↗

arXiv2008

Feedback Scheduling: An Event-Driven Paradigm

Embedded computing systems today increasingly feature resource constraints and workload variability, which lead to uncertainty in resource availability. This raises great challenges to software design and programming in multitasking environments. In this paper, the emerging methodology of feedback scheduling is introduced to address these challenges. As a closed-loop approach to resource management, feedback scheduling promises to enhance the flexibility and resource efficiency of various software programs through dynamically distributing available resources among concurrent tasks based on feedback information about the actual usage of the resources. With emphasis on the behavioral design of feedback schedulers, we describe a general framework of feedback scheduling in the context of real-time control applications. A simple yet illustrative feedback scheduling algorithm is given. From a programming perspective, we describe how to modify the implementation of control tasks to facilitate the application of feedback scheduling. An event-driven paradigm that combines time-triggered and event-triggered approaches is proposed for programming of the feedback scheduler. Simulation results argue that the proposed event-driven paradigm yields better performance than time-triggered paradigm in dynamic environments where the workload varies irregularly and unpredictably.

cs.OS↗

arXiv2008

Local Read-Write Operations in Sensor Networks

Designing protocols and formulating convenient programming units of abstraction for sensor networks is challenging due to communication errors and platform constraints. This paper investigates properties and implementation reliability for a \emph{local read-write} abstraction. Local read-write is inspired by the class of read-modify-write operations defined for shared-memory multiprocessor architectures. The class of read-modify-write operations is important in solving consensus and related synchronization problems for concurrency control. Local read-write is shown to be an atomic abstraction for synchronizing neighborhood states in sensor networks. The paper compares local read-write to similar lightweight operations in wireless sensor networks, such as read-all, write-all, and a transaction-based abstraction: for some optimistic scenarios, local read-write is a more efficient neighborhood operation. A partial implementation is described, which shows that three outcomes characterize operation response: success, failure, and cancel. A failure response indicates possible inconsistency for the operation result, which is the result of a timeout event at the operation's initiator. The paper presents experimental results on operation performance with different timeout values and situations of no contention, with some tests also on various neighborhood sizes.

cs.OS↗

arXiv2008

Interface Matching and Combining Techniques for Services Integration

The development of many highly dynamic environments, like pervasive environments, introduces the possibility to use geographically close-related services. Dynamically integrating and unintegrating these services in running applications is a key challenge for this use. In this article, we classify service integration issues according to interfaces exported by services and internal combining techniques. We also propose a contextual integration service, IntegServ, and an interface, Integrable, for developing services.

cs.OS↗