A communication framework for distributed access control in microkernel-based systems

Microkernel-based architectures have gained an increasing interest and relevance for embedded systems. These can not only provide real-time guarantees but also offer strong security properties which become increasingly significant in certain application domains such as automotive systems. Nevertheless, the functionality of those complex systems often needs to be distributed across a network of control units for various reasons (e.g. physical location, scalability, separation). Although microkernels have been commercially established, distributed systems like these have not been a major focus. This is basically originated by the fact that – in the microkernel world – policy, device drivers and protocol stacks are userspace concerns and rather left to be solved by the particular application domain. Following the principle of least privilege, we therefore developed a distributed access-control framework for all network-based communication in microkernel-based systems that can be generically deployed. Our design not only enforces security properties such as integrity but is also scalable without adding too much overhead in terms of run time or code

Undermining Isolation through Covert Channels in the Fiasco.OC Microkernel

In the new age of cyberwars, system designers have come to recognize the merits of building critical systems on top of small kernels for their ability to provide strong isolation at system level. This is due to the fact that enforceable isolation is the prerequisite for any reasonable security policy. Towards this goal we examine some internals of Fiasco.OC, a microkernel of the prominent L4 family. Despite its recent success in certain highsecurity projects for governmental use, we prove that Fiasco.OC is not suited to ensure strict isolation between components meant to be separated. Unfortunately, in addition to the construction of system-wide denial of service attacks, our identified weaknesses of Fiasco.OC also allow covert channels across security perimeters with high bandwidth. We verified our results in a strong affirmative way through many practical experiments. Indeed, for all potential use cases of Fiasco.OC we implemented a full-fledged system on its respective archetypical hardware: Desktop server/workstation on AMD64 x86 CPU, Tablet on Intel Atom CPU, Smartphone on ARM Cortex A9 CPU. The measured peak channel capacities ranging from 13500 bits/s (Cortex-A9 device) to 30500 bits/s (desktop system) lay bare the feeble meaningfulness of Fiasco. OC’s isolation guarantee. This proves that Fiasco.OC cannot be used as a separation kernel within high-security areas

SHILL: A Secure Shell Scripting Language

The Principle of Least Privilege suggests that software should be executed with no more authority than it requires to accomplish its task. Current security tools make it difficult to apply this principle: they either require significant modifications to applications or do not facilitate reasoning about combining untrustworthy components. We propose SHILL, a secure shell scripting language. SHILL scripts enable compositional reasoning about security through contracts that limit the effects of script execution, including the effects of programs invoked by the script. SHILL contracts are declarative security policies that act as documentation for consumers of SHILL scripts, and are enforced through a combination of language design and sandboxing. We have implemented a prototype of SHILL for FreeBSD and used it for several case studies including a grading script and a script to download, compile, and install software. Our experience indicates that SHILL is a practical and useful system security tool, and can provide fine-grained security guarantees.Engineering and Applied Science

Operating System Support for Redundant Multithreading

Failing hardware is a fact and trends in microprocessor design indicate that the fraction of hardware suffering from permanent and transient faults will continue to increase in future chip generations. Researchers proposed various solutions to this issue with different downsides: Specialized hardware components make hardware more expensive in production and consume additional energy at runtime. Fault-tolerant algorithms and libraries enforce specific programming models on the developer. Compiler-based fault tolerance requires the source code for all applications to be available for recompilation. In this thesis I present ASTEROID, an operating system architecture that integrates applications with different reliability needs. ASTEROID is built on top of the L4/Fiasco.OC microkernel and extends the system with Romain, an operating system service that transparently replicates user applications. Romain supports single- and multi-threaded applications without requiring access to the application's source code. Romain replicates applications and their resources completely and thereby does not rely on hardware extensions, such as ECC-protected memory. In my thesis I describe how to efficiently implement replication as a form of redundant multithreading in software. I develop mechanisms to manage replica resources and to make multi-threaded programs behave deterministically for replication. I furthermore present an approach to handle applications that use shared-memory channels with other programs. My evaluation shows that Romain provides 100% error detection and more than 99.6% error correction for single-bit flips in memory and general-purpose registers. At the same time, Romain's execution time overhead is below 14% for single-threaded applications running in triple-modular redundant mode. The last part of my thesis acknowledges that software-implemented fault tolerance methods often rely on the correct functioning of a certain set of hardware and software components, the Reliable Computing Base (RCB). I introduce the concept of the RCB and discuss what constitutes the RCB of the ASTEROID system and other fault tolerance mechanisms. Thereafter I show three case studies that evaluate approaches to protecting RCB components and thereby aim to achieve a software stack that is fully protected against hardware errors

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

Ein mehrschichtiges sicheres Framework für Fahrzeugsysteme

In recent years, significant developments were introduced within the vehicular domain, evolving the vehicles to become a network of many embedded systems distributed throughout the car, known as Electronic Control Units (ECUs). Each one of these ECUs runs a number of software components that collaborate with each other to perform various vehicle functions. Modern vehicles are also equipped with wireless communication technologies, such as WiFi, Bluetooth, and so on, giving them the capability to interact with other vehicles and roadside infrastructure. While these improvements have increased the safety of the automotive system, they have vastly expanded the attack surface of the vehicle and opened the door for new potential security risks. The situation is made worse by a lack of security mechanisms in the vehicular system which allows the escalation of a compromise in one of the non-critical sub-systems to threaten the safety of the entire vehicle and its passengers. This dissertation focuses on providing a comprehensive framework that ensures the security of the vehicular system during its whole life-cycle. This framework aims to prevent the cyber-attacks against different components by ensuring secure communications among them. Furthermore, it aims to detect attacks which were not prevented successfully, and finally, to respond to these attacks properly to ensure a high degree of safety and stability of the system.In den letzten Jahren wurden bedeutende Entwicklungen im Bereich der Fahrzeuge vorgestellt, die die Fahrzeuge zu einem Netzwerk mit vielen im gesamten Fahrzeug verteile integrierte Systeme weiterentwickelten, den sogenannten Steuergeräten (ECU, englisch = Electronic Control Units). Jedes dieser Steuergeräte betreibt eine Reihe von Softwarekomponenten, die bei der Ausführung verschiedener Fahrzeugfunktionen zusammenarbeiten. Moderne Fahrzeuge sind auch mit drahtlosen Kommunikationstechnologien wie WiFi, Bluetooth usw. ausgestattet, die ihnen die Möglichkeit geben, mit anderen Fahrzeugen und der straßenseitigen Infrastruktur zu interagieren. Während diese Verbesserungen die Sicherheit des Fahrzeugsystems erhöht haben, haben sie die Angriffsfläche des Fahrzeugs erheblich vergrößert und die Tür für neue potenzielle Sicherheitsrisiken geöffnet. Die Situation wird durch einen Mangel an Sicherheitsmechanismen im Fahrzeugsystem verschärft, die es ermöglichen, dass ein Kompromiss in einem der unkritischen Subsysteme die Sicherheit des gesamten Fahrzeugs und seiner Insassen gefährdet kann. Diese Dissertation konzentriert sich auf die Entwicklung eines umfassenden Rahmens, der die Sicherheit des Fahrzeugsystems während seines gesamten Lebenszyklus gewährleistet. Dieser Rahmen zielt darauf ab, die Cyber-Angriffe gegen verschiedene Komponenten zu verhindern, indem eine sichere Kommunikation zwischen ihnen gewährleistet wird. Darüber hinaus zielt es darauf ab, Angriffe zu erkennen, die nicht erfolgreich verhindert wurden, und schließlich auf diese Angriffe angemessen zu reagieren, um ein hohes Maß an Sicherheit und Stabilität des Systems zu gewährleisten

A New System Architecture for Heterogeneous Compute Units

The ongoing trend to more heterogeneous systems forces us to rethink the design of systems. In this work, I study a new system design that considers heterogeneous compute units (general-purpose cores with different instruction sets, DSPs, FPGAs, fixed-function accelerators, etc.) from the beginning instead of as an afterthought. The goal is to treat all compute units (CUs) as first-class citizens, enabling (1) isolation and secure communication between all types of CUs, (2) a direct interaction of all CUs, removing the conventional CPU from the critical path, and (3) access to operating system (OS) services such as file systems and network stacks for all CUs. To study this system design, I am using a hardware/software co-design based on two key ideas: 1) introduce a new hardware component next to each CU used by the OS as the CUs' common interface and 2) let the OS kernel control applications remotely from a different CU. The hardware component is called data transfer unit (DTU) and offers the minimal set of features to reach the stated goals: secure message passing and memory access. The OS is called M³ and runs its kernel on a dedicated CU and runs the OS services and applications on the remaining CUs. The kernel is responsible for establishing DTU-based communication channels between services and applications. After a channel has been set up, services and applications communicate directly without involving the kernel. This approach allows to support arbitrary CUs as aforementioned first-class citizens, ranging from fixed-function accelerators to complex general-purpose cores