[v4,bpf-next,0/7] Add fd_array_cnt attribute for BPF_PROG_LOAD

Message

Anton Protopopov Dec. 3, 2024, 1:50 p.m. UTC

Add a new attribute to the bpf(BPF_PROG_LOAD) system call. If this
new attribute is non-zero, then the fd_array is considered to be a
continuous array of the fd_array_cnt length and to contain only
proper map file descriptors or btf file descriptors.

This change allows maps, which aren't referenced directly by a BPF
program, to be bound to the program _and_ also to be present during
the program verification (so BPF_PROG_BIND_MAP is not enough for this
use case).

The primary reason for this change is that it is a prerequisite for
adding "instruction set" maps, which are both non-referenced by the
program and must be present during the program verification.

The first four commits add the new functionality, the fifth adds
corresponding self-tests, and the last two are small additional fixes.

v1 -> v2:
  * rewrite the add_fd_from_fd_array() function (Eduard)
  * a few cleanups in selftests (Eduard)

v2 -> v3:
  * various renamings (Alexei)
  * "0 is not special" (Alexei, Andrii)
  * do not alloc memory on fd_array init (Alexei)
  * fix leaking maps for error path (Hou Tao)
  * use libbpf helpers vs. raw syscalls (Andrii)
  * add comments on __btf_get_by_fd/__bpf_map_get (Alexei)
  * remove extra code (Alexei)

v3 -> v4:
  * simplify error path when parsing fd_array
  * libbpf: pass fd_array_cnt only in prog_load (Alexei)
  * selftests patch contained extra code (Alexei)
  * renames, fix comments (Alexei)

Anton Protopopov (7):
  bpf: add a __btf_get_by_fd helper
  bpf: move map/prog compatibility checks
  bpf: add fd_array_cnt attribute for prog_load
  libbpf: prog load: allow to use fd_array_cnt
  selftests/bpf: Add tests for fd_array_cnt
  bpf: fix potential error return
  selftest/bpf: replace magic constants by macros

 include/linux/bpf.h                           |  17 +
 include/linux/btf.h                           |   2 +
 include/uapi/linux/bpf.h                      |  10 +
 kernel/bpf/btf.c                              |  13 +-
 kernel/bpf/core.c                             |   6 +-
 kernel/bpf/syscall.c                          |   2 +-
 kernel/bpf/verifier.c                         | 193 ++++++----
 tools/include/uapi/linux/bpf.h                |  10 +
 tools/lib/bpf/bpf.c                           |   3 +-
 tools/lib/bpf/bpf.h                           |   5 +-
 .../selftests/bpf/prog_tests/fd_array.c       | 340 ++++++++++++++++++
 tools/testing/selftests/bpf/progs/syscall.c   |   6 +-
 12 files changed, 524 insertions(+), 83 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/fd_array.c