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Christian Brauner <brauner@kernel.org> says: binfmt_misc has exactly one execution model where the registered interpreter becomes the executed program and the matched binary is handed to it as an argument. For wine or qemu-user that is the point. For a per-binary loader it is backwards. The interpreter is an implementation detail of running the binary, yet it owns the entire process identity: - argv[0] and /proc/pid/cmdline show the interpreter invocation, not what the caller executed. - /proc/self/exe names the interpreter. Relocatable programs commonly locate themselves through it and find the dynamic linker instead. - A binary passed to execveat() as an inaccessible O_CLOEXEC fd cannot run at all as the interpreter has no path to open it by. - gdb cross-validates AT_ENTRY/AT_PHDR against the exe file and discards the load displacement on mismatch leaving PIE symbols unrelocated. This series adds two dispatch modes that close the gap from opposite ends: (1) transparent dispatch Registered with the 'T' flag or chosen per exec with BPF_BINPRM_TRANSPARENT. The binary is sent to the interpreter through AT_EXECFD, the argument vector stays exactly as the caller built it, and the kernel labels mm->exe_file and comm with the binary. A new AT_FLAGS_TRANSPARENT_INTERP aux vector bit is raised indicating that nothing was spliced, argv belongs to the program, and to load it from the descriptor. The interpreter keeps control of mapping the binary, so the mode covers foreign architectures and non-ELF payloads. The exe label is not a new privilege. It names precisely the file the caller passed to execve(), not a file of the process's choosing. That file is permission-checked, write-denied while the process runs and recorded by audit. Credential derivation does not change exactly as today. (2) loader substitution The kernel executes the matched binary natively as the main image and substitutes the registered interpreter for the binary's PT_INTERP. binfmt_misc functions as a PT_INTERP override. There is no contract and no identity to reconstruct. So a stock dynamic loader works unchanged. Hence, 'L' is for native-arch ELF with PT_INTERP. The two modes compose. A bpf handler reads the ELF header from bprm->buf and grades per binary, picking 'L' where it applies and 'T' or classic dispatch for the rest. If userspace control over relocation is wanted 'T' is the way to go. * patches from https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-0-e57866e4ae0f@kernel.org: (21 commits) binfmt_misc: document loader substitution selftests/exec: test binfmt_misc loader substitution binfmt_misc: let a bpf handler request loader substitution binfmt_misc: add the 'L' loader substitution flag binfmt_elf_fdpic: consume a stashed PT_INTERP substitute binfmt_elf: consume a stashed PT_INTERP substitute exec: carry a PT_INTERP substitute in struct linux_binprm binfmt_misc: document the transparent identity contract selftests/exec: test the transparent binfmt_misc mode binfmt_misc: let a bpf handler run the interpreter transparently binfmt_misc: add a static transparent flag 'T' binfmt_misc: add transparent interpreter dispatch exec: label mm->exe_file with the binary for a transparent dispatch exec: add AT_FLAGS_TRANSPARENT_INTERP selftests/exec: convert the binfmt_misc bpf test to the kselftest harness exec: release the replaced file with do_close_execat() binfmt_misc: split out entry_open_interpreter() and build_interp_argv() binfmt_misc: normalize the per-exec invocation flags binfmt_misc: table-drive the register string flags docs, binfmt_misc: keep general usage out of the handler sections ... Link: https://patch.msgid.link/20260721-work-bpf-binfmt_misc-ptinterp-v2-0-e57866e4ae0f@kernel.org Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst