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Frühjahrs- und Herbsttreffen der Fachgruppen

https://dl.gi.de/handle/20.500.12116/30631
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Auflistung Frühjahrs- und Herbsttreffen der Fachgruppen nach Titel

1 - 10 von 26
  • Textdokument
    Beastie In For Checkup: Analyzing FreeBSD with LockDoc
    (Tagungsband des FG-BS Herbsttreffens 2021, 2021) Lochmann, Alexander; Schirmeier, Horst
    LockDoc is an approach to extract locking rules for kernel data structures, based on a dynamic execution trace. The recorded trace can e.g. be used to verify existing locking documentation. LockDoc results for Linux indicated that only 53 % of all examined data types were accessed consistently with their respective locking documentation [5]: Linux systematically elides locks for performance reasons, and the existing documentation is partially outdated or inconsistent. Without a solid “ground truth”, it is impossible to reliably attribute LockDoc’s findings to bugs in Linux, or to issues with the LockDoc approach itself. Therefore, in this paper we present results from applying LockDoc to a much more straightforwardly and “cleanly” implemented operating system: FreeBSD offers sophisticated locking documentation – e.g. for many data structures, each individual field is annotated with a precise locking rule. We report that, for four centrally documented data types, FreeBSD adheres to the documented locking rules in 72.4 % of all dynamic data-structure accesses. Investigating the remaining rule-violating accesses, we already triggered two commits for the FreeBSD kernel fixing unprotected accesses, and nudge this value to 73.6 %.
  • Textdokument
    Developing Bare-Metal GPGPU Drivers From Scratch: What prevents scientists from developing own GPGPU drivers?
    (Tagungsband des FG-BS Frühjahrstreffens 2021, 2021) Lütke Dreimann, Marcel; Kessener, Daniel
    Most of modern computers use Graphic Processing Units (GPUs) as an additional source of computing power. However, using GPUs in bare-metal research operating systems comes with some challenges. Existing drivers for Linux or Windows are complex and cannot be used for without much effort. Documentation of modern GPUs is often missing or incomplete and drivers are incomprehensive or closed source. This paper tries to explain what prevents scientists from creating their own GPU drivers. Additionally, it gives an overview about GPGPU driver development for GPUs from different manufactur- ers and shows some challenges. Nevertheless, we have ambitiously started an undertaking to develop our own driver from scratch. To some extend this was successful, but with many problems on the way.
  • Textdokument
    DMA Security in the Presence of IOMMUs
    (Tagungsband des FG-BS Frühjahrstreffens 2022, 2022) Schwarz, Christian; Reusch, Viktor; Planeta, Maksym
    Faulty, vulnerable or malicious PCIe devices can harm a system through DMA. IOMMUs can act as a security mechanism to protect against this problem by restricting the memory that is accessible via DMA. Unfortunately, there are methods to bypass the IOMMU restrictions. This paper is a survey over the currently existing bypasses and their feasibility. Current systems might be exploited from any untrusted source of DMA, which includes peripheral PCIe devices, virtual machines using SR-IOV, and even RDMA network cards, which enable remote attacks. Key strategies for the attacks presented here are Rowhammer, cache side-channels, and the exploitation of weaknesses in device drivers, e.g., for network cards, or protocols like PCIe or Ethernet OAM. An attacker can potentially achieve denial of service, the reading of confidential data, and even arbitrary code execution. Fortunately, there are some precautions to reduce the risks for affected systems.
  • Textdokument
    Efficient Checkpointing in Byzantine Fault-Tolerant Systems
    (Tagungsband des FB-SYS Herbsttreffens 2019, 2019) Eischer, Michael; Distler, Tobias
    Distributed Byzantine fault-tolerant systems require frequent checkpoints of the application state to perform periodic garbage collection and enable faulty replicas to recover efficiently. State-of-the-art checkpointing approaches for replicated systems either cause significant service disruption when the application state is large, or they are unable to produce checkpoints that are verifiable across replicas. To address these problems we developed and evaluated deterministic fuzzy checkpointing, a technique to create consistent and verifiable checkpoints in parallel with request execution.
  • Textdokument
    First Things First: A Discussion of Modelling Approaches for Disruptive Memory Technologies
    (Tagungsband des FG-BS Herbsttreffens 2021, 2021) Müller, Michael; Kessener, Daniel; Spinczyk, Olaf
    Disruptive memory technologies (DMT) are dramatically changing the architecture of modern computer systems and affect important design decisions throughout the whole software stack. For their success it is crucial that developers of system software and applications find ways to fully exploit the potential of the novel hardware. Having appropriate DMT hardware models is the key to successful optimization in the world of system software and application development. Therefore, this paper introduces four relevant new DMTs and corresponding performance analyzes as well as modelling approaches. We conclude with the insight that there is a lack of system-wide models that are practically applicable by system software designers for proper optimization and, thus, an important domain for future research.
  • Textdokument
    Full-Scale File System Acceleration on GPU
    (Tagungsband des FG-BS Frühjahrstreffens 2024, 2024) Maucher, Peter; Kittner, Lennard; Rath,Nico; Lucka,Gregor; Werling,Lukas; Khalil,Yussuf; Gröninger,Thorsten; Bellosa,Frank
    Modern HPC and AI Computing solutions regularly use GPUs as their main source of computational power. This creates a significant imbalance for storage operations for GPU applications, as every such storage operation has to be signalled to and handled by the CPU. In GPU4FS, we propose a radical solution to this imbalance: Move the file system implementation to the application, and run the complete file system on the GPU. This requires multiple changes to the complete file system stack, from the actual storage layout up to the file system interface. Additionally, this approach frees the CPU from file system management tasks, which allows for more meaningful usage of the CPU. In our pre- liminary implementation, we show that a fully-featured file system running on GPU with minimal CPU interaction is possible, and even bandwidth-competitive depending on the underlying storage medium.
  • Textdokument
    Group-based Memory Management in Fyr
    (Tagungsband des FG-BS Herbsttreffens 2020, 2020) Weis, Torben; Zdankin, Peter; Carl, Oskar; Waltereit, Marian
    Albeit being introduced decades ago, C and C++ are still the most commonly used programming languages for operating systems. These languages have no reliable mechanisms to deal with memory safety issues, such as use-after-free or data race conditions, that are a leading cause for security bugs in operating systems and other critical software. Tools such as Valgrind have been developed to identify errors, but the errors must occur during the analysis, as they are not found otherwise. Several modern programming languages such as Rust, Go and Swift have emerged aiming to solve some of the issues by providing memory safety guarantees at compile or run time. However, these languages introduce new limitations, especially concerning software development for performance-critical or resource-constrained systems. In this paper, we introduce a new approach to automatic memory management that manages the lifetime of object groups instead of individual objects. We show that group-based memory management can remove some of the restrictions of modern programming languages while satisfying important memory safety constraints. Furthermore, we show how group-based memory management is implemented in our new systems programming language Fyr.
  • Textdokument
    Improvements in Crash Consistency Testing for Persistent Memory File Systems
    (Tagungsband des FG-BS Frühjahrstreffens 2024, 2024) Werling, Lukas; Oder, Thomas-Christian; Wäldele, Lucas; Ritz, Daniel; Bellosa, Frank
    Achieving crash consistency in persistent memory (PM) applications is difficult due to the need for fine-granular cache flushes and memory fences. File systems are no exception. Previous works have found numerous bugs in PM file systems, but crash consistency testing as part of file system development is still rare. With this paper, we make crash consistency testing easier by improving Vinter, a crash consistency testing tool for file systems based on virtual machines. We introduce support for cross-media file systems with NVMe and PM that are not covered by other testing tools. To speed up testing, we add an alternative algorithm for simulating crashes that focuses on logic bugs rather than misuse of PM primitives.
  • Textdokument
    Improving Linux-Kernel Tests for LockDoc with Feedback-driven Fuzzing
    (Tagungsband des FG-BS Herbsttreffens 2020, 2020) Lochmann, Alexander; Thunig, Robin; Schirmeier, Horst
    LockDoc is an approach to extract locking rules for kernel data structures from a dynamic execution trace recorded while the system is under a benchmark load. These locking rules can e.g. be used to locate synchronization bugs. For high rule precision and thorough bug finding, the approach heavily depends on the choice of benchmarks: They must trigger the execution of as much code as possible in the kernel subsystem relevant for the targeted data structures. However, existing test suites such as those provided by the Linux Test Project (LTP) only achieve – in the case of LTP – about 35 percent basic-block coverage for the VFS subsystem, which is the relevant subsystem when extracting locking rules for filesystem-related data structures. In this article, we discuss how to complement the LTP suites to improve the code coverage for our LockDoc scenario. We repurpose syzkaller – a coverage-guided fuzzer with the goal to validate the robustness of kernel APIs – to 1) not aim for kernel crashes, and to 2) maximize code coverage for a specific kernel subsystem. Thereby, we generate new benchmark programs that can be run in addition to the LTP, and increase VFS basic-block coverage by 26.1 percent.
  • Textdokument
    In Microservices We Trust — Do Microservices Solve Resilience Challenges?
    (Tagungsband des FB-SYS Herbsttreffens 2019, 2019) Hilbrich, Marcus
    Resilience is an open challenge. In this paper we look into microservices – a concept that argues to be resilient. We look into the definition of microservices and argue whether the definition provides the promised advantages regarding to resilience.