Latest From LWN: Kernel, firmware, shadow-utils

posted by Roy Schestowitz on Aug 20, 2026

• GNU/Linux

  • Kernel Space / File Systems / Virtualization

    • LWN ☛ Bringing BPF to binfmt_misc

      The kernel is able to run a few types of executable files, including native binaries in the ELF format and interpreted programs that begin with the #! marker. It also, however, has a mechanism, called binfmt_misc, that can be configured from user space to enable the transparent execution of programs in just about any format. This feature has been relatively static for years, but it seems likely to receive some significant updates in the near future, including the ability to load BPF programs that can decide how to run a given program.

    • LWN ☛ Even more formal verification for BPF

      BPF offers useful safety guarantees, but Kumar Kartikeya Dwivedi wants BPF programs to be even safer. At the 2026 Linux Storage, Filesystem, Memory-Management, and BPF Summit, he led a session (slides) discussing the possibility of adding domain-specific invariants to BPF programs. It was not a discussion intended to lead to the implementation of any particular kernel feature, but rather an overview of why additional formal verification might be needed, and how it could work with the existing BPF ecosystem.

      The BPF verifier ensures that BPF programs cannot violate kernel invariants. They cannot acquire locks in the wrong context, call kernel functions with arguments of the incorrect type, etc. Individual places in the kernel that make use of BPF programs can impose additional requirements. For example, sched_ext has a watchdog that will kick out a BPF program that does not schedule a runnable task within a certain amount of time. All of this is necessary, but not sufficient, Dwivedi said.

    • LWN ☛ KVM planes head for takeoff [LWN.net]

      Virtualization places a guest system into a separate security domain, typically with fewer privileges than software running directly on the host. Increasingly, there is interest in creating multiple security domains within a single virtualized system as well. CPU vendors (and software vendors too) are implementing solutions; each of which, of course, is different from all of the others. KVM planes, currently under development by Jörg Rödel, Paolo Bonzini, and others in the KVM community, is an attempt to provide an abstraction layer that makes all of these features available on Linux systems; it is not a small task.

      When an operating-system kernel launches within a virtual machine, it typically has full access to all aspects of that machine. Interest in confidential computing, though, is driving efforts to split up that access. So, for example, a virtual machine may have a smaller kernel within it that is charged with implementing a trusted platform module (TPM) in software; if the virtual machine as a whole can manipulate that TPM, its results cannot be trusted. But if the TPM has its own range of memory that only it can access (and which might be encrypted to strengthen that protection) and its CPU state cannot be changed from the containing VM, then it should be secure — until somebody inevitably figures out a way to break that security, of course.

    • LWN ☛ Block-layer error injection

      Storage code has to cope with hardware that fails in inconvenient ways, but coaxing a healthy disk into producing those failures on demand, for testing, is usually not possible. The kernel provides several ways to inject block-layer I/O errors, but none of those can select the operation to fail, pick the status code to return, or target a disk directly without employing a stacked device on top. Use of a stacked device means the test runs against the mapper device, not the disk it was meant to exercise. A patch series from Christoph Hellwig adds a configurable error-injection interface that does all three things that the current error-injection code lacks, controlled by a per-disk debugfs file.

• Systems

  • Open Hardware/Modding

    • LWN ☛ A look at CrossPoint e-reader firmware [LWN.net]

      There are a number of small, inexpensive, low-powered e-reader or e-paper devices that have promise as ebook readers with one minor problem: the firmware they ship with does not realize their full potential. To solve that problem, the CrossPoint Reader project looks to provide replacement firmware that offers necessary features, better performance, and a more pleasant reading experience. On August 7, the project released version 1.5.0, which opens large EPUBs more quickly, provides offline dictionary lookups, and has reworked settings for changing layout and font options. The release also improves support for right-to-left text as well as Chinese, Japanese, and Korean (CJK) text rendering.

• Leftovers

  • Security

    • LWN ☛ Changes in shadow-utils password-expiration features [LWN.net]

      The shadow-utils project provides the tools that handle /etc/shadow, /etc/passwd, and other related databases; in general, it manages users and groups on many Linux systems. While most software releases are notable for what is added, the recent shadow-utils 4.20.0 release is most noteworthy for what has been removed. Specifically, several utilities and functionality related to periodic password expiry, which were deprecated in the December 2025 4.19.0 release, have been removed as planned. It is still possible to manage some aspects of password aging with shadow-utils, but organizations that depend on such features should start planning for their complete removal within a few years.