[PATCH bpf-next v4 00/10] bpf: Introduce file dynptr

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

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 parses the executable’s ELF to
locate thread-local symbol information, demonstrating the file dynptr
workflow end-to-end.

Changelog:
---
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

Mykyta Yatsenko (10):
  selftests/bpf: remove unnecessary kfunc prototypes
  bpf: widen dynptr size/offset to 64 bit
  lib: move freader into buildid.h
  lib/freader: support reading more than 2 folios
  bpf: verifier: centralize const dynptr check in
    unmark_stack_slots_dynptr()
  bpf: add plumbing for file-backed dynptr
  bpf: add kfuncs and helpers support for file dynptrs
  bpf: verifier: refactor kfunc specialization
  bpf: dispatch to sleepable file dynptr
  selftests/bpf: add file dynptr tests

 MAINTAINERS                                   |   1 +
 include/linux/bpf.h                           |  30 +--
 include/linux/buildid.h                       |  25 +++
 include/uapi/linux/bpf.h                      |   8 +-
 kernel/bpf/helpers.c                          | 173 ++++++++++++++----
 kernel/bpf/log.c                              |   2 +
 kernel/bpf/verifier.c                         | 157 ++++++++++------
 kernel/trace/bpf_trace.c                      |  46 ++---
 lib/buildid.c                                 |  56 ++----
 tools/include/uapi/linux/bpf.h                |   8 +-
 tools/testing/selftests/bpf/bpf_kfuncs.h      |  12 +-
 .../selftests/bpf/prog_tests/file_reader.c    | 113 ++++++++++++
 .../selftests/bpf/progs/dynptr_success.c      |  12 +-
 .../testing/selftests/bpf/progs/file_reader.c | 145 +++++++++++++++
 .../selftests/bpf/progs/file_reader_fail.c    |  52 ++++++
 .../selftests/bpf/progs/ip_check_defrag.c     |   5 -
 .../bpf/progs/verifier_netfilter_ctx.c        |   5 -
 17 files changed, 655 insertions(+), 195 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/file_reader.c
 create mode 100644 tools/testing/selftests/bpf/progs/file_reader.c
 create mode 100644 tools/testing/selftests/bpf/progs/file_reader_fail.c

-- 
2.51.0