Advancing Operating Systems via Aspect-Oriented Programming

Operating system kernels are among the most complex pieces of software in existence to- day. Maintaining the kernel code and developing new functionality is increasingly compli- cated, since the amount of required features has risen significantly, leading to side ef fects that can be introduced inadvertedly by changing a piece of code that belongs to a completely dif ferent context. Software developers try to modularize their code base into separate functional units. Some of the functionality or “concerns” required in a kernel, however, does not fit into the given modularization structure; this code may then be spread over the code base and its implementation tangled with code implementing dif ferent concerns. These so-called “crosscutting concerns” are especially dif ficult to handle since a change in a crosscutting concern implies that all relevant locations spread throughout the code base have to be modified. Aspect-Oriented Software Development (AOSD) is an approach to handle crosscutting concerns by factoring them out into separate modules. The “advice” code contained in these modules is woven into the original code base according to a pointcut description, a set of interaction points (joinpoints) with the code base. To be used in operating systems, AOSD requires tool support for the prevalent procedu- ral programming style as well as support for weaving aspects. Many interactions in kernel code are dynamic, so in order to implement non-static behavior and improve performance, a dynamic weaver that deploys and undeploys aspects at system runtime is required. This thesis presents an extension of the “C” programming language to support AOSD. Based on this, two dynamic weaving toolkits – TOSKANA and TOSKANA-VM – are presented to permit dynamic aspect weaving in the monolithic NetBSD kernel as well as in a virtual- machine and microkernel-based Linux kernel running on top of L4. Based on TOSKANA, applications for this dynamic aspect technology are discussed and evaluated. The thesis closes with a view on an aspect-oriented kernel structure that maintains coherency and handles crosscutting concerns using dynamic aspects while enhancing de- velopment methods through the use of domain-specific programming languages

Vulnerability detection in device drivers

Tese de doutoramento, Informática (Ciência da Computação), Universidade de Lisboa, Faculdade de Ciências, 2017The constant evolution in electronics lets new equipment/devices to be regularly made available on the market, which has led to the situation where common operating systems (OS) include many device drivers(DD) produced by very diverse manufactures. Experience has shown that the development of DD is error prone, as a majority of the OS crashes can be attributed to flaws in their implementation. This thesis addresses the challenge of designing methodologies and tools to facilitate the detection of flaws in DD, contributing to decrease the errors in this kind of software, their impact in the OS stability, and the security threats caused by them. This is especially relevant because it can help developers to improve the quality of drivers during their implementation or when they are integrated into a system. The thesis work started by assessing how DD flaws can impact the correct execution of the Windows OS. The employed approach used a statistical analysis to obtain the list of kernel functions most used by the DD, and then automatically generated synthetic drivers that introduce parameter errors when calling a kernel function, thus mimicking a faulty interaction. The experimental results showed that most targeted functions were ineffective in the defence of the incorrect parameters. A reasonable number of crashes and a small number of hangs were observed suggesting a poor error containment capability of these OS functions. Then, we produced an architecture and a tool that supported the automatic injection of network attacks in mobile equipment (e.g., phone), with the objective of finding security flaws (or vulnerabilities) in Wi-Fi drivers. These DD were selected because they are of easy access to an external adversary, which simply needs to create malicious traffic to exploit them, and therefore the flaws in their implementation could have an important impact. Experiments with the tool uncovered a previously unknown vulnerability that causes OS hangs, when a specific value was assigned to the TIM element in the Beacon frame. The experiments also revealed a potential implementation problem of the TCP-IP stack by the use of disassociation frames when the target device was associated and authenticated with a Wi-Fi access point. Next, we developed a tool capable of registering and instrumenting the interactions between a DD and the OS. The solution used a wrapper DD around the binary of the driver under test, enabling full control over the function calls and parameters involved in the OS-DD interface. This tool can support very diverse testing operations, including the log of system activity and to reverse engineer the driver behaviour. Some experiments were performed with the tool, allowing to record the insights of the behaviour of the interactions between the DD and the OS, the parameter values and return values. Results also showed the ability to identify bugs in drivers, by executing tests based on the knowledge obtained from the driver’s dynamics. Our final contribution is a methodology and framework for the discovery of errors and vulnerabilities in Windows DD by resorting to the execution of the drivers in a fully emulated environment. This approach is capable of testing the drivers without requiring access to the associated hardware or the DD source code, and has a granular control over each machine instruction. Experiments performed with Off the Shelf DD confirmed a high dependency of the correctness of the parameters passed by the OS, identified the precise location and the motive of memory leaks, the existence of dormant and vulnerable code.A constante evolução da eletrónica tem como consequência a disponibilização regular no mercado de novos equipamentos/dispositivos, levando a uma situação em que os sistemas operativos (SO) mais comuns incluem uma grande quantidade de gestores de dispositivos (GD) produzidos por diversos fabricantes. A experiência tem mostrado que o desenvolvimento dos GD é sujeito a erros uma vez que a causa da maioria das paragens do SO pode ser atribuída a falhas na sua implementação. Esta tese centra-se no desafio da criação de metodologias e ferramentas que facilitam a deteção de falhas nos GD, contribuindo para uma diminuição nos erros neste tipo de software, o seu impacto na estabilidade do SO, e as ameaças de segurança por eles causadas. Isto é especialmente relevante porque pode ajudar a melhorar a qualidade dos GD tanto na sua implementação como quando estes são integrados em sistemas. Este trabalho inicia-se com uma avaliação de como as falhas nos GD podem levar a um funcionamento incorreto do SO Windows. A metodologia empregue usa uma análise estatística para obter a lista das funções do SO que são mais utilizadas pelos GD, e posteriormente constrói GD sintéticos que introduzem erros nos parâmetros passados durante a chamada às funções do SO, e desta forma, imita a integração duma falta. Os resultados das experiências mostraram que a maioria das funções testadas não se protege eficazmente dos parâmetros incorretos. Observou-se a ocorrência de um número razoável de paragens e um pequeno número de bloqueios, o que sugere uma pobre capacidade das funções do SO na contenção de erros. Posteriormente, produzimos uma arquitetura e uma ferramenta que suporta a injeção automática de ataques em equipamentos móveis (e.g., telemóveis), com o objetivo de encontrar falhas de segurança (ou vulnerabilidades) em GD de placas de rede Wi-Fi. Estes GD foram selecionados porque são de fácil acesso a um atacante remoto, o qual apenas necessita de criar tráfego malicioso para explorar falhas na sua implementação podendo ter um impacto importante. As experiências realizadas com a ferramenta revelaram uma vulnerabilidade anteriormente desconhecida que provoca um bloqueio no SO quando é atribuído um valor específico ao campo TIM da mensagem de Beacon. As experiências também revelaram um potencial problema na implementação do protocolo TCP-IP no uso das mensagens de desassociação quando o dispositivo alvo estava associado e autenticado com o ponto de acesso Wi-Fi. A seguir, desenvolvemos uma ferramenta com a capacidade de registar e instrumentar as interações entre os GD e o SO. A solução usa um GD que envolve o código binário do GD em teste, permitindo um controlo total sobre as chamadas a funções e aos parâmetros envolvidos na interface SO-GD. Esta ferramenta suporta diversas operações de teste, incluindo o registo da atividade do sistema e compreensão do comportamento do GD. Foram realizadas algumas experiências com esta ferramenta, permitindo o registo das interações entre o GD e o SO, os valores dos parâmetros e os valores de retorno das funções. Os resultados mostraram a capacidade de identificação de erros nos GD, através da execução de testes baseados no conhecimento da dinâmica do GD. A nossa contribuição final é uma metodologia e uma ferramenta para a descoberta de erros e vulnerabilidades em GD Windows recorrendo à execução do GD num ambiente totalmente emulado. Esta abordagem permite testar GD sem a necessidade do respetivo hardware ou o código fonte, e possuí controlo granular sobre a execução de cada instrução máquina. As experiências realizadas com GD disponíveis comercialmente confirmaram a grande dependência que os GD têm nos parâmetros das funções do SO, e identificaram o motivo e a localização precisa de fugas de memória, a existência de código não usado e vulnerável

A Raspberry Pi controlling neuromorphic hardware

This thesis describes the integration of a Raspberry Pi, a credit-card-sized single board computer, into the Wafer Scale Integration (WSI) System of the BrainScaleS project. The Raspberry Pi’s task is to bundle all the interfaces necessary to manage the system’s elaborate power supply into one single-access, easy-to-use interface. To this purpose the Raspberry Pi replaced the former evaluation board responsible for power management, taking over all of its tasks and in addition providing faster and cheaper hardware. The integration took place in two main steps: configuring the Raspberry Pi’s hardware and adapting the control programme from the former board to the new hardware. The results of this thesis are the successful integration of the Raspberry Pi into the WSI system, which was proven by several communication tests between the Raspberry Pi and the rest of the system, and an easy-to-follow step-by-step guide on how to set up Raspberry Pis to manage additional systems

A Study of Initialization in Linux and OpenBSD

The code that initializes a system can be notoriously difficult to understand. In secure systems, initialization is critical for establishing a starting state that is secure. This paper explores two architectures used for bringing an operating system to its initial state, once the operating system gains control from the boot loader. Specifically, the ways in which the OpenBSD and Linux operating systems handle initialization are dissected

Secure Virtualization of Latency-Constrained Systems

Virtualization is a mature technology in server and desktop environments where multiple systems are consolidate onto a single physical hardware platform, increasing the utilization of todays multi-core systems as well as saving resources such as energy, space and costs compared to multiple single systems. Looking at embedded environments reveals that many systems use multiple separate computing systems inside, including requirements for real-time and isolation properties. For example, modern high-comfort cars use up to a hundred embedded computing systems. Consolidating such diverse configurations promises to save resources such as energy and weight. In my work I propose a secure software architecture that allows consolidating multiple embedded software systems with timing constraints. The base of the architecture builds a microkernel-based operating system that supports a variety of different virtualization approaches through a generic interface, supporting hardware-assisted virtualization and paravirtualization as well as multiple architectures. Studying guest systems with latency constraints with regards to virtualization showed that standard techniques such as high-frequency time-slicing are not a viable approach. Generally, guest systems are a combination of best-effort and real-time work and thus form a mixed-criticality system. Further analysis showed that such systems need to export relevant internal scheduling information to the hypervisor to support multiple guests with latency constraints. I propose a mechanism to export those relevant events that is secure, flexible, has good performance and is easy to use. The thesis concludes with an evaluation covering the virtualization approach on the ARM and x86 architectures and two guest operating systems, Linux and FreeRTOS, as well as evaluating the export mechanism

Multi-Persona Mobile Computing

Smartphones and tablets are increasingly ubiquitous, and many users rely on multiple mobile devices to accommodate work, personal, and geographic mobility needs. Pervasive access to always-on mobile computing has created new security and privacy concerns for mobile devices that often force users to carry multiple devices to meet those needs. The volume and popularity of mobile devices has commingled hardware and software design, and created tightly vertically integrated platforms that lock users into a single, vendor controlled ecosystem. My thesis is that lightweight mechanisms can be added to commodity operating systems to enable multiple virtual phones or tablets to run at the same time on a physical smartphone or tablet device, and to enable apps from multiple mobile platforms, such as iOS and Android, to run together on the same physical device, all while maintaining the low-latency and responsiveness expected of modern mobile devices. This dissertation presents two lightweight operating systems mechanisms, virtualization and binary compatibility, that enable multi-persona mobile computing. First, we present Cells, a mobile virtualization architecture enabling multiple virtual phones, or personas, to run simultaneously on the same physical cellphone in a secure and isolated manner. Cells introduces device namespaces that allow apps to run in a virtualized environment while still leveraging native devices such as GPUs to provide accelerated graphics. Second, we present Cycada, an operating system compatibility architecture that runs applications built for different mobile ecosystems, iOS and Android, together on a single Android device. Cycada introduces kernel-level code adaptation and diplomats to simplify binary compatibility support by reusing existing operating system code and unmodified frameworks and libraries. Both Cells and Cycada have been implemented in Android, and can run multiple Android virtual phones, and a mix of iOS and Android apps on the same device with good performance. Because mobile computing has become increasingly important, we also present a new way to teach operating systems in a mobile-centric way that incorporates the concepts of geographic mobility, sensor data acquisition, and resource-constrained design considerations

LibrettOS: A Dynamically Adaptable Multiserver-Library OS

We present LibrettOS, an OS design that fuses two paradigms to simultaneously address issues of isolation, performance, compatibility, failure recoverability, and run-time upgrades. LibrettOS acts as a microkernel OS that runs servers in an isolated manner. LibrettOS can also act as a library OS when, for better performance, selected applications are granted exclusive access to virtual hardware resources such as storage and networking. Furthermore, applications can switch between the two OS modes with no interruption at run-time. LibrettOS has a uniquely distinguishing advantage in that, the two paradigms seamlessly coexist in the same OS, enabling users to simultaneously exploit their respective strengths (i.e., greater isolation, high performance). Systems code, such as device drivers, network stacks, and file systems remain identical in the two modes, enabling dynamic mode switching and reducing development and maintenance costs. To illustrate these design principles, we implemented a prototype of LibrettOS using rump kernels, allowing us to reuse existent, hardened NetBSD device drivers and a large ecosystem of POSIX/BSD-compatible applications. We use hardware (VM) virtualization to strongly isolate different rump kernel instances from each other. Because the original rumprun unikernel targeted a much simpler model for uniprocessor systems, we redesigned it to support multicore systems. Unlike kernel-bypass libraries such as DPDK, applications need not be modified to benefit from direct hardware access. LibrettOS also supports indirect access through a network server that we have developed. Applications remain uninterrupted even when network components fail or need to be upgraded. Finally, to efficiently use hardware resources, applications can dynamically switch between the indirect and direct modes based on their I/O load at run-time. [full abstract is in the paper]Comment: 16th ACM SIGPLAN/SIGOPS International Conference on Virtual Execution Environments (VEE '20), March 17, 2020, Lausanne, Switzerlan

Doctor of Philosophy

dissertationA modern software system is a composition of parts that are themselves highly complex: operating systems, middleware, libraries, servers, and so on. In principle, compositionality of interfaces means that we can understand any given module independently of the internal workings of other parts. In practice, however, abstractions are leaky, and with every generation, modern software systems grow in complexity. Traditional ways of understanding failures, explaining anomalous executions, and analyzing performance are reaching their limits in the face of emergent behavior, unrepeatability, cross-component execution, software aging, and adversarial changes to the system at run time. Deterministic systems analysis has a potential to change the way we analyze and debug software systems. Recorded once, the execution of the system becomes an independent artifact, which can be analyzed offline. The availability of the complete system state, the guaranteed behavior of re-execution, and the absence of limitations on the run-time complexity of analysis collectively enable the deep, iterative, and automatic exploration of the dynamic properties of the system. This work creates a foundation for making deterministic replay a ubiquitous system analysis tool. It defines design and engineering principles for building fast and practical replay machines capable of capturing complete execution of the entire operating system with an overhead of several percents, on a realistic workload, and with minimal installation costs. To enable an intuitive interface of constructing replay analysis tools, this work implements a powerful virtual machine introspection layer that enables an analysis algorithm to be programmed against the state of the recorded system through familiar terms of source-level variable and type names. To support performance analysis, the replay engine provides a faithful performance model of the original execution during replay

SecureQEMU: Emulation-based Software Protection Providing Encrypted Code Execution and Page Granularity Code Signing

This research presents an original emulation-based software protection scheme providing protection from reverse code engineering (RCE) and software exploitation using encrypted code execution and page-granularity code signing, respectively. Protection mechanisms execute in trusted emulators while remaining out-of-band of untrusted systems being emulated. This protection scheme is called SecureQEMU and is based on a modified version of Quick Emulator (QEMU) [5]. RCE is a process that uncovers the internal workings of a program. It is used during vulnerability and intellectual property (IP) discovery. To protect from RCE program code may have anti-disassembly, anti-debugging, and obfuscation techniques incorporated. These techniques slow the process of RCE, however, once defeated protected code is still comprehensible. Encryption provides static code protection, but encrypted code must be decrypted before execution. SecureQEMUs\u27 scheme overcomes this limitation by keeping code encrypted during execution. Software exploitation is a process that leverages design and implementation errors to cause unintended behavior which may result in security policy violations. Traditional exploitation protection mechanisms provide a blacklist approach to software protection. Specially crafted exploit payloads bypass these protection mechanisms. SecureQEMU provides a whitelist approach to software protection by executing signed code exclusively. Unsigned malicious code (exploits, backdoors, rootkits, etc.) remain unexecuted, therefore, protecting the system. SecureQEMUs\u27 cache mechanisms increase performance by 0.9% to 1.8% relative to QEMU. Emulation overhead for SecureQEMU varies from 1400% to 2100% with respect to native performance. SecureQEMUs\u27 performance increase is negligible with respect to emulation overhead. Dependent on risk management strategy, SecureQEMU\u27s protection benefits may outweigh emulation overhead