published_or_final_version / Computer Science / Master / Master of Philosophy

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In this dissertation, we examine some of the challenges faced by the emerging networked storage systems. We focus on two main issues. Current file systems allocate storage statically at the time of their creation. This results in many suboptimal scenarios, for example: (a) space on the disk is not allocated well across multiple file systems, (b) data is not organized well for typical access patterns. We propose Virtual Allocation for flexible storage allocation. Virtual allocation separates storage allocation from the file system. It employs an allocate-on-write strategy, which lets applications fit into the actual usage of storage space without regard to the configured file system size. This improves flexibility by allowing storage space to be shared across different file systems. We present the design of virtual allocation and an evaluation of it through benchmarks based on a prototype system on Linux. Next, based on virtual allocation, we consider the problem of balancing locality and load in networked storage systems with multiple storage devices (or bricks). Data distribution affects locality and load balance across the devices in a networked storage system. We propose user-optimal data migration scheme which tries to balance locality and load balance in such networked storage systems. The presented approach automatically and transparently manages migration of data blocks among disks as data access patterns and loads change over time. We built a prototype system on Linux and present the design of user-optimal migration and an evaluation of it through realistic experiments.

Thesis (Ph. D.)--OGI School of Science & Engineering at OHSU, 2003. / Includes bibliographical references (leaves 170-181).

Computer hardware and software evolve very fast. With the advent of chip-multiprocessors and symmetric multithreading, multiprocessor hardware configurations are becoming prevalent. For software, new hardware and requirements such as security, performance and maintainability drive the development of new runtime environments, virtual machines and programming methodologies. These trends present problems when porting legacy software. Multiprocessor hardware require ports of uniprocessor operating system kernels while new software environments might require that programs have to be ported to different languages. This thesis examines the tradeoff between performance and development effort for software porting with case studies in operating system porting to multiprocessors and tool support for porting C and C++ applications to Java virtual machines. The thesis consists of seven papers. The first paper is a survey of existing multiprocessor development approaches and focuses on the tradeoff between performance and implementation effort. The second and third papers describe the evolution a traditional lock-based multiprocessor port, going from a serialized “giant locked” port and evolving into a coarse-grained implementation. The fourth paper instead presents an alternative porting approach which aims to minimize development effort. The fifth paper describes a tool for efficient instrumentation of programs, which can be used during the development of large software systems such as operating system kernels. The sixth and seventh papers finally describe a binary translator which translates MIPS binaries into Java bytecode to allow low-effort porting of C and C++ applications to Java virtual machines. The first main contributions of this thesis is an in-depth investigation of the techniques used when porting operating system kernels to multiprocessors, focusing on development effort and performance. The traditional approach used in the second and third papers required longer development time than expected, and the alternative approach in the fourth paper can therefore be preferable in some cases. The second main contribution is the development of a binary translator that targets portability of C and C++ applications to J2ME devices. The last two papers show that the approach is functional and has good enough performance to be feasible in real-life situations.

Operating system kernels present a difficult security challenge. Despite their millions of lines of code and broad, complex attack surface, they remain a trusted component shared between all applications. If an attacker can combine an exploit for any application on a system with a kernel exploit or privilege escalation, the attacker can then control any other application, regardless of whether the second application was itself vulnerable. This dissertation presents two hypervisor-based systems: OSck, which increases the trustworthiness of a guest kernel by detecting kernel rootkits, and InkTag, which removes the need for an application to trust the kernel at all. Vital to both systems is their use of information from a potentially malicious kernel. These systems rely on information from the kernel about its own functionality to make their implementation simpler, more efficient, and more secure. Importantly, although they rely on this information, they do not trust it. A kernel that lies about its functionality to appear benign will be detected, as will a kernel that simply acts maliciously. OSck detects kernel rootkits: malicious software programs that are particularly difficult to detect because they modify internal kernel operation to hide their presence. Running concurrently with an operating system and isolated by the hypervisor, OSck verifies safety properties for large portions of the kernel heap with minimal overhead, by deducing type information from unmodified kernel source code and in-memory kernel data structures. InkTag gives strong safety guarantees to trusted applications, even in the presence of a malicious operating system. InkTag isolates applications from the operating system, and enables applications to validate that the kernel is acting in good faith, for example by ensuring that the kernel is mapping the correct file data into the application's address space. InkTag introduces paraverification, a technique that simplifies the InkTag hypervisor by forcing the untrusted operating system to participate in its own verification. InkTag requires that the kernel prove to the hypervisor that its updates to application state (such as page tables) are valid, and also to prove to the application that its responses to system calls are consistent. InkTag is also the first system of its kind to implement access control, secure naming, and consistency for data on stable storage. / text

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