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Mykyta Yatsenko says: ==================== bpf: Introduce file dynptr From: Mykyta Yatsenko <yatsenko@meta.com> This series adds a new dynptr kind, file dynptr, which enables BPF programs to perform safe reads from files in a structured way. Initial motivations include: * Parsing the executable’s ELF to locate thread-local variable symbols * Capturing stack traces when frame pointers are disabled By leveraging the existing dynptr abstraction, we reuse the verifier’s lifetime/size checks and keep the API consistent with existing dynptr read helpers. Technical details: 1. Reuses the existing freader library to read files a folio at a time. 2. bpf_dynptr_slice() and bpf_dynptr_read() always copy data from folios into a program-provided buffer; zero-copy access is intentionally not supported to keep it simple. 3. Reads may sleep if the requested folios are not in the page cache. 4. Few verifier changes required: * Support dynptr destruction in kfuncs * Add kfunc address substitution based on whether the program runs in a sleepable or non-sleepable context. Testing: The final patch adds a selftest that validates BPF program reads the same data as userspace, page faults are enabled in sleepable context and disabled in non-sleepable. Changelog: --- v4 -> v5 v4: https://lore.kernel.org/all/20251021200334.220542-1-mykyta.yatsenko5@gmail.com/ * Inlined and removed kfunc_call_imm(), run overflow check for call_imm only if !bpf_jit_supports_far_kfunc_call(). v3 -> v4 v3: https://lore.kernel.org/bpf/20251020222538.932915-1-mykyta.yatsenko5@gmail.com/ * Remove ringbuf usage from selftests * bpf_dynptr_set_null(ptr) when discarding file dynptr * call kfunc_call_imm() in specialize_kfunc() only, removed call from add_kfunc_call() v2 -> v3 v2: https://lore.kernel.org/bpf/20251015161155.120148-1-mykyta.yatsenko5@gmail.com/ * Add negative tests * Rewrote tests to use LSM for bpf_get_task_exe_file() * Move call_imm overflow check into kfunc_call_imm() v1 -> v2 v1: https://lore.kernel.org/bpf/20251003160416.585080-1-mykyta.yatsenko5@gmail.com/ * Remove ELF parsing selftest * Expanded u32 -> u64 refactoring, changes in include/uapi/linux/bpf.h * Removed freader.{c,h}, instead move freader definitions into buildid.h. * Small refactoring of the multiple folios reading algorithm * Directly return error after unmark_stack_slots_dynptr(). * Make kfuncs receive trusted arguments. * Remove enum bpf_is_sleepable, use bool instead * Remove unnecessary sorting from specialize_kfunc() * Remove bool kfunc_in_sleepable_ctx; field from the struct bpf_insn_aux_data, rely on non_sleepable field introduced by Kumar * Refactor selftests, do madvise(...MADV_PAGEOUT) for all pages read by the test * Introduce the test for non-sleepable case, verify it fails with -EFAULT ==================== Link: https://lore.kernel.org/r/20251026203853.135105-1-mykyta.yatsenko5@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.