add new acquire/release BPF kfuncs

G'day All,

The original cover letter providing background context and motivating
factors around the needs for the BPF kfuncs introduced within this
patch series can be found here [0], so please do reference that if
need be.

Notably, one of the main contention points within v1 of this patch
series was that we were effectively leaning on some preexisting
in-kernel APIs such as get_task_exe_file() and get_mm_exe_file()
within some of the newly introduced BPF kfuncs. As noted in my
response here [1] though, I struggle to understand the technical
reasoning behind why exposing such in-kernel helpers, specifically
only to BPF LSM program types in the form of BPF kfuncs, is inherently
a terrible idea. So, until someone provides me with a sound technical
explanation as to why this cannot or should not be done, I'll continue
to lean on them. The alternative is to reimplement the necessary
in-kernel APIs within the BPF kfuncs, but that's just nonsensical IMO.

Changes since v1:
   * Dropped the probe-read related patches [2, 3], which focused on
     retroactively fixing bpf_d_path() such that it's susceptability
     to memory corruption issues is drastically reduced. Rightfully so
     though, it was deemed that reimplementing a semi-functional
     variant of d_path() that was effectively backed by
     copy_from_kernel_nofault() is suboptimal.

[0] https://lore.kernel.org/bpf/cover.1708377880.git.mattbobr...
[1] https://lore.kernel.org/bpf/ZdX83H7rTEwMYvs2@google.com/
[2] https://lore.kernel.org/bpf/5643840bd57d0c2345635552ae228...
[3] https://lore.kernel.org/bpf/18c7b587d43bbc7e80593bf51ea9d...

Matt Bobrowski (9):
  bpf: rename fs_kfunc_set_ids to lsm_kfunc_set_ids
  bpf: add new acquire/release BPF kfuncs for mm_struct
  bpf/selftests: add selftests for mm_struct acquire/release BPF kfuncs
  bpf: add new acquire/release based BPF kfuncs for exe_file
  bpf/selftests: add selftests for exe_file acquire/release BPF kfuncs
  bpf: add acquire/release based BPF kfuncs for fs_struct's paths
  bpf/selftests: add selftests for root/pwd path based BPF kfuncs
  bpf: add trusted d_path() based BPF kfunc bpf_path_d_path()
  bpf/selftests: adapt selftests test_d_path for BPF kfunc
    bpf_path_d_path()

 kernel/trace/bpf_trace.c                      | 248 +++++++++++++++++-
 .../testing/selftests/bpf/prog_tests/d_path.c |  80 ++++++
 .../selftests/bpf/prog_tests/exe_file_kfunc.c |  49 ++++
 .../selftests/bpf/prog_tests/mm_kfunc.c       |  48 ++++
 .../selftests/bpf/prog_tests/path_kfunc.c     |  48 ++++
 .../selftests/bpf/progs/d_path_common.h       |  35 +++
 .../bpf/progs/d_path_kfunc_failure.c          |  66 +++++
 .../bpf/progs/d_path_kfunc_success.c          |  25 ++
 .../bpf/progs/exe_file_kfunc_common.h         |  23 ++
 .../bpf/progs/exe_file_kfunc_failure.c        | 181 +++++++++++++
 .../bpf/progs/exe_file_kfunc_success.c        |  52 ++++
 .../selftests/bpf/progs/mm_kfunc_common.h     |  19 ++
 .../selftests/bpf/progs/mm_kfunc_failure.c    | 103 ++++++++
 .../selftests/bpf/progs/mm_kfunc_success.c    |  30 +++
 .../selftests/bpf/progs/path_kfunc_common.h   |  20 ++
 .../selftests/bpf/progs/path_kfunc_failure.c  | 114 ++++++++
 .../selftests/bpf/progs/path_kfunc_success.c  |  30 +++
 .../testing/selftests/bpf/progs/test_d_path.c |  20 +-
 .../bpf/progs/test_d_path_check_rdonly_mem.c  |   8 +-
 .../bpf/progs/test_d_path_check_types.c       |   8 +-
 20 files changed, 1160 insertions(+), 47 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/exe_file_kfunc.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/mm_kfunc.c
 create mode 100644 tools/testing/selftests/bpf/prog_tests/path_kfunc.c
 create mode 100644 tools/testing/selftests/bpf/progs/d_path_common.h
 create mode 100644 tools/testing/selftests/bpf/progs/d_path_kfunc_failure.c
 create mode 100644 tools/testing/selftests/bpf/progs/d_path_kfunc_success.c
 create mode 100644 tools/testing/selftests/bpf/progs/exe_file_kfunc_common.h
 create mode 100644 tools/testing/selftests/bpf/progs/exe_file_kfunc_failure.c
 create mode 100644 tools/testing/selftests/bpf/progs/exe_file_kfunc_success.c
 create mode 100644 tools/testing/selftests/bpf/progs/mm_kfunc_common.h
 create mode 100644 tools/testing/selftests/bpf/progs/mm_kfunc_failure.c
 create mode 100644 tools/testing/selftests/bpf/progs/mm_kfunc_success.c
 create mode 100644 tools/testing/selftests/bpf/progs/path_kfunc_common.h
 create mode 100644 tools/testing/selftests/bpf/progs/path_kfunc_failure.c
 create mode 100644 tools/testing/selftests/bpf/progs/path_kfunc_success.c

-- 
2.44.0.278.ge034bb2e1d-goog

/M