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At least 253 records · Page 14Linked to original sources

arXiv2017

A Reconnaissance Attack Mechanism for Fixed-Priority Real-Time Systems

In real-time embedded systems (RTS), failures due to security breaches can cause serious damage to the system, the environment and/or injury to humans. Therefore, it is very important to understand the potential threats and attacks against these systems. In this paper we present a novel reconnaissance attack that extracts the exact schedule of real-time systems designed using fixed priority scheduling algorithms. The attack is demonstrated on both a real hardware platform and a simulator, with a high success rate. Our evaluation results show that the algorithm is robust even in the presence of execution time variation.

cs.CR↗

arXiv2017

IOTune: A G-states Driver for Elastic Performance of Block Storage

Imagining a disk which provides baseline performance at a relatively low price during low-load periods, but when workloads demand more resources, the disk performance is automatically promoted in situ and in real time. In a hardware era, this is hardly achievable. However, this imagined disk is becoming reality due to the technical advances of software-defined storage, which enable volume performance to be adjusted on the fly. We propose IOTune, a resource management middleware which employs software-defined storage primitives to implement G-states of virtual block devices. G-states enable virtual block devices to serve at multiple performance gears, getting rid of conflicts between immutable resource reservation and dynamic resource demands, and always achieving resource right-provisioning for workloads. Accompanying G-states, we also propose a new block storage pricing policy for cloud providers. Our case study for applying G-states to cloud block storage verifies the effectiveness of the IOTune framework. Trace-replay based evaluations demonstrate that storage volumes with G-states adapt to workload fluctuations. For tenants, G-states enable volumes to provide much better QoS with a same cost of ownership, comparing with static IOPS provisioning and the I/O credit mechanism. G-states also reduce I/O tail latencies by one to two orders of magnitude. From the standpoint of cloud providers, G-states promote storage utilization, creating values and benefiting competitiveness. G-states supported by IOTune provide a new paradigm for storage resource management and pricing in multi-tenant clouds.

cs.OS↗

arXiv2017

Comments on "Gang EDF Schedulability Analysis"

This short report raises a correctness issue in the schedulability test presented in Kato et al., "Gang EDF Scheduling of Parallel Task Systems", 30th IEEE Real-Time Systems Symposium, 2009, pp. 459-468.

cs.OS↗

arXiv2017

Look Mum, no VM Exits! (Almost)

Multi-core CPUs are a standard component in many modern embedded systems. Their virtualisation extensions enable the isolation of services, and gain popularity to implement mixed-criticality or otherwise split systems. We present Jailhouse, a Linux-based, OS-agnostic partitioning hypervisor that uses novel architectural approaches to combine Linux, a powerful general-purpose system, with strictly isolated special-purpose components. Our design goals favour simplicity over features, establish a minimal code base, and minimise hypervisor activity. Direct assignment of hardware to guests, together with a deferred initialisation scheme, offloads any complex hardware handling and bootstrapping issues from the hypervisor to the general purpose OS. The hypervisor establishes isolated domains that directly access physical resources without the need for emulation or paravirtualisation. This retains, with negligible system overhead, Linux's feature-richness in uncritical parts, while frugal safety and real-time critical workloads execute in isolated, safe domains.

cs.OS↗

arXiv2017

GPU System Calls

GPUs are becoming first-class compute citizens and are being tasked to perform increasingly complex work. Modern GPUs increasingly support programmability- enhancing features such as shared virtual memory and hardware cache coherence, enabling them to run a wider variety of programs. But a key aspect of general-purpose programming where GPUs are still found lacking is the ability to invoke system calls. We explore how to directly invoke generic system calls in GPU programs. We examine how system calls should be meshed with prevailing GPGPU programming models where thousands of threads are organized in a hierarchy of execution groups: Should a system call be invoked at the individual GPU task, or at different execution group levels? What are reasonable ordering semantics for GPU system calls across these hierarchy of execution groups? To study these questions, we implemented GENESYS -- a mechanism to allow GPU pro- grams to invoke system calls in the Linux operating system. Numerous subtle changes to Linux were necessary, as the existing kernel assumes that only CPUs invoke system calls. We analyze the performance of GENESYS using micro-benchmarks and three applications that exercise the filesystem, networking, and memory allocation subsystems of the kernel. We conclude by analyzing the suitability of all of Linux's system calls for the GPU.

cs.OS↗

arXiv2017

MITHRIL: Mining Sporadic Associations for Cache Prefetching

The growing pressure on cloud application scalability has accentuated storage performance as a critical bottle- neck. Although cache replacement algorithms have been extensively studied, cache prefetching - reducing latency by retrieving items before they are actually requested remains an underexplored area. Existing approaches to history-based prefetching, in particular, provide too few benefits for real systems for the resources they cost. We propose MITHRIL, a prefetching layer that efficiently exploits historical patterns in cache request associations. MITHRIL is inspired by sporadic association rule mining and only relies on the timestamps of requests. Through evaluation of 135 block-storage traces, we show that MITHRIL is effective, giving an average of a 55% hit ratio increase over LRU and PROBABILITY GRAPH, a 36% hit ratio gain over AMP at reasonable cost. We further show that MITHRIL can supplement any cache replacement algorithm and be readily integrated into existing systems. Furthermore, we demonstrate the improvement comes from MITHRIL being able to capture mid-frequency blocks.

cs.PF↗

arXiv2017

SMORE: A Cold Data Object Store for SMR Drives (Extended Version)

Shingled magnetic recording (SMR) increases the capacity of magnetic hard drives, but it requires that each zone of a disk be written sequentially and erased in bulk. This makes SMR a good fit for workloads dominated by large data objects with limited churn. To explore this possibility, we have developed SMORE, an object storage system designed to reliably and efficiently store large, seldom-changing data objects on an array of host-managed or host-aware SMR disks. SMORE uses a log-structured approach to accommodate the constraint that all writes to an SMR drive must be sequential within large shingled zones. It stripes data across zones on separate disks, using erasure coding to protect against drive failure. A separate garbage collection thread reclaims space by migrating live data out of the emptiest zones so that they can be trimmed and reused. An index stored on flash and backed up to the SMR drives maps object identifiers to on-disk locations. SMORE interleaves log records with object data within SMR zones to enable index recovery after a system crash (or failure of the flash device) without any additional logging mechanism. SMORE achieves full disk bandwidth when ingesting data---with a variety of object sizes---and when reading large objects. Read performance declines for smaller object sizes where inter- object seek time dominates. With a worst-case pattern of random deletions, SMORE has a write amplification (not counting RAID parity) of less than 2.0 at 80% occupancy. By taking an index snapshot every two hours, SMORE recovers from crashes in less than a minute. More frequent snapshots allow faster recovery.

cs.OS↗

arXiv2017

Downgrade Attack on TrustZone

Security-critical tasks require proper isolation from untrusted software. Chip manufacturers design and include trusted execution environments (TEEs) in their processors to secure these tasks. The integrity and security of the software in the trusted environment depend on the verification process of the system. We find a form of attack that can be performed on the current implementations of the widely deployed ARM TrustZone technology. The attack exploits the fact that the trustlet (TA) or TrustZone OS loading verification procedure may use the same verification key and may lack proper rollback prevention across versions. If an exploit works on an out-of-date version, but the vulnerability is patched on the latest version, an attacker can still use the same exploit to compromise the latest system by downgrading the software to an older and exploitable version. We did experiments on popular devices on the market including those from Google, Samsung and Huawei, and found that all of them have the risk of being attacked. Also, we show a real-world example to exploit Qualcomm's QSEE. In addition, in order to find out which device images share the same verification key, pattern matching schemes for different vendors are analyzed and summarized.

cs.CR↗

arXiv2018

Deterministic Memory Abstraction and Supporting Multicore System Architecture

Poor time predictability of multicore processors has been a long-standing challenge in the real-time systems community. In this paper, we make a case that a fundamental problem that prevents efficient and predictable real-time computing on multicore is the lack of a proper memory abstraction to express memory criticality, which cuts across various layers of the system: the application, OS, and hardware. We, therefore, propose a new holistic resource management approach driven by a new memory abstraction, which we call Deterministic Memory. The key characteristic of deterministic memory is that the platform - the OS and hardware - guarantees small and tightly bounded worst-case memory access timing. In contrast, we call the conventional memory abstraction as best-effort memory in which only highly pessimistic worst-case bounds can be achieved. We propose to utilize both abstractions to achieve high time predictability but without significantly sacrificing performance. We present deterministic memory-aware OS and architecture designs, including OS-level page allocator, hardware-level cache, and DRAM controller designs. We implement the proposed OS and architecture extensions on Linux and gem5 simulator. Our evaluation results, using a set of synthetic and real-world benchmarks, demonstrate the feasibility and effectiveness of our approach.

cs.AR↗

arXiv2017

Study and Analysis of MAC/IPAD Lab Configuration

This paper is about three virtualization modes: VMware, Parallels, and Boot Camping. The trade off of their testing is the hardware requirements. The main question is, among the three, which is the most suitable? The answer actually varies from user to user. It depends on the user needs. Moreover, it is necessary to consider its performance, graphics, efficiency and reliability, and interoperability, and that is our major scope. In order to take the final decision in choosing one of the modes it is important to run some tests, which costs a lot in terms of money, complexity, and time consumption. Therefore, in order to overcome this trade off, most of the research has been done through online benchmarking and my own anticipation. The final solution was extracted after comparing all previously mentioned above and after rigorous testing made which will be introduced later in this document.

cs.OS↗

arXiv2017

Optimizations of Management Algorithms for Multi-Level Memory Hierarchy

In the near future the SCM is predicted to modify the form of new programs, the access form to storage, and the way that storage devices themselves are built. Therefore, a combination between the SCM and a designated Memory Allocation Manager (MAM) that will allow the programmer to manually control the different memories in the memory hierarchy will be likely to achieve a new level of performance for memory-aware data structures. Although the manual MAM seems to be the optimal approach for multi-level memory hierarchy management, this technique is still very far from being realistic, and the chances that it would be implemented in current codes using High Performance Computing (HPC) platforms is quite low. This premise means that the most reasonable way to introduce the SCM into any usable and popular memory system would be by implementing an automated version of the MAM using the fundamentals of paging algorithms, as used for two-level memory hierarchy. Our hypothesis is that achieving appropriate transferability between memory levels may be possible using ideas of algorithms employed in current virtual memory systems, and that the adaptation of those algorithms from a two-level memory hierarchy to an N-level memory hierarchy is possible. In order to reach the conclusion that our hypothesis is correct, we investigated various paging algorithms, and found the ones that could be adapted successfully from two-level memory hierarchy to an N-level memory hierarchy. We discovered that using an adaptation of the Aging paging algorithm to an N-level memory hierarchy results in the best performances in terms of Hit/Miss ratio. In order to verify our hypothesis we build a simulator called "DeMemory simulator" for analyzing our algorithms as well as for other algorithms that will be devised in the future.

cs.OS↗

arXiv2017

FluidMem: Memory as a Service for the Datacenter

Disaggregating resources in data centers is an emerging trend. Recent work has begun to explore memory disaggregation, but suffers limitations including lack of consideration of the complexity of cloud-based deployment, including heterogeneous hardware and APIs for cloud users and operators. In this paper, we present FluidMem, a complete system to realize disaggregated memory in the datacenter. Going beyond simply demonstrating remote memory is possible, we create an entire Memory as a Service. We define the requirements of Memory as a Service and build its implementation in Linux as FluidMem. We present a performance analysis of FluidMem and demonstrate that it transparently supports remote memory for standard applications such as MongoDB and genome sequencing applications.

cs.OS↗

arXiv2017

Analyzing IO Amplification in Linux File Systems

We present the first systematic analysis of read, write, and space amplification in Linux file systems. While many researchers are tackling write amplification in key-value stores, IO amplification in file systems has been largely unexplored. We analyze data and metadata operations on five widely-used Linux file systems: ext2, ext4, XFS, btrfs, and F2FS. We find that data operations result in significant write amplification (2-32X) and that metadata operations have a large IO cost. For example, a single rename requires 648 KB write IO in btrfs. We also find that small random reads result in read amplification of 2-13X. Based on these observations, we present the CReWS conjecture about the relationship between IO amplification, consistency, and storage space utilization. We hope this paper spurs people to design future file systems with less IO amplification, especially for non-volatile memory technologies.

cs.OS↗

arXiv2017

Entirely protecting operating systems against transient errors in space environment

In this article, we propose a mainly-software hardening technique to totally protect unmodified running operating systems on COTS hardware against transient errors in heavily radiation - flooded environment like high altitude space. The technique is currently being implemented in a hypervisor and allows to control the upper layers of the software stack (operating system and applications). The rest of the system, the hypervisor, will be protected by other means, thus resulting in a completely protected system against transient errors. The induced overhead turns around 200% but this is expected to decrease with future improvements.

cs.OS↗

arXiv2017

Bringing Fault-Tolerant GigaHertz-Computing to Space: A Multi-Stage Software-Side Fault-Tolerance Approach for Miniaturized Spacecraft

Modern embedded technology is a driving factor in satellite miniaturization, contributing to a massive boom in satellite launches and a rapidly evolving new space industry. Miniaturized satellites, however, suffer from low reliability, as traditional hardware-based fault-tolerance (FT) concepts are ineffective for on-board computers (OBCs) utilizing modern systems-on-a-chip (SoC). Therefore, larger satellites continue to rely on proven processors with large feature sizes. Software-based concepts have largely been ignored by the space industry as they were researched only in theory, and have not yet reached the level of maturity necessary for implementation. We present the first integral, real-world solution to enable fault-tolerant general-purpose computing with modern multiprocessor-SoCs (MPSoCs) for spaceflight, thereby enabling their use in future high-priority space missions. The presented multi-stage approach consists of three FT stages, combining coarse-grained thread-level distributed self-validation, FPGA reconfiguration, and mixed criticality to assure long-term FT and excellent scalability for both resource constrained and critical high-priority space missions. Early benchmark results indicate a drastic performance increase over state-of-the-art radiation-hard OBC designs and considerably lower software- and hardware development costs. This approach was developed for a 4-year European Space Agency (ESA) project, and we are implementing a tiled MPSoC prototype jointly with two industrial partners.

cs.DC↗

arXiv2017

Tug-of-War: Observations on Unified Content Handling

Modern applications and Operating Systems vary greatly with respect to how they register and identify different types of content. These discrepancies lead to exploits and inconsistencies in user experience. In this paper, we highlight the issues arising in the modern content handling ecosystem, and examine how the operating system can be used to achieve unified and consistent content identification.

cs.CR↗

arXiv2017

Performance Evaluation of Container-based Virtualization for High Performance Computing Environments

Virtualization technologies have evolved along with the development of computational environments since virtualization offered needed features at that time such as isolation, accountability, resource allocation, resource fair sharing and so on. Novel processor technologies bring to commodity computers the possibility to emulate diverse environments where a wide range of computational scenarios can be run. Along with processors evolution, system developers have created different virtualization mechanisms where each new development enhanced the performance of previous virtualized environments. Recently, operating system-based virtualization technologies captured the attention of communities abroad (from industry to academy and research) because their important improvements on performance area. In this paper, the features of three container-based operating systems virtualization tools (LXC, Docker and Singularity) are presented. LXC, Docker, Singularity and bare metal are put under test through a customized single node HPL-Benchmark and a MPI-based application for the multi node testbed. Also the disk I/O performance, Memory (RAM) performance, Network bandwidth and GPU performance are tested for the COS technologies vs bare metal. Preliminary results and conclusions around them are presented and discussed.

cs.OS↗

arXiv2017

The Case for a Single System Image for Personal Devices

Computing technology has gotten cheaper and more powerful, allowing users to have a growing number of personal computing devices at their disposal. While this trend is beneficial for the user, it also creates a growing management burden for the user. Each device must be managed independently and users must repeat the same management tasks on the each device, such as updating software, changing configurations, backup, and replicating data for availability. To prevent the management burden from increasing with the number of devices, we propose that all devices run a single system image called a personal computing image. Personal computing images export a device-specific user interface on each device, but provide a consistent view of application and operating state across all devices. As a result, management tasks can be performed once on any device and will be automatically propagated to all other devices belonging to the user. We discuss evolutionary steps that can be taken to achieve personal computing images for devices and elaborate on challenges that we believe building such systems will face.

cs.OS↗