[PATCH bpf-next v4 00/12] bpf: add bpf_for_each_map_elem() helper

[Yonghong Song <yhs@fb.com>]

This patch set introduced bpf_for_each_map_elem() helper.
The helper permits bpf program iterates through all elements
for a particular map.

The work originally inspired by an internal discussion where
firewall rules are kept in a map and bpf prog wants to
check packet 5 tuples against all rules in the map.
A bounded loop can be used but it has a few drawbacks.
As the loop iteration goes up, verification time goes up too.
For really large maps, verification may fail.
A helper which abstracts out the loop itself will not have
verification time issue.

A recent discussion in [1] involves to iterate all hash map
elements in bpf program. Currently iterating all hashmap elements
in bpf program is not easy if key space is really big.
Having a helper to abstract out the loop itself is even more
meaningful.

The proposed helper signature looks like:
  long bpf_for_each_map_elem(map, callback_fn, callback_ctx, flags)
where callback_fn is a static function and callback_ctx is
a piece of data allocated on the caller stack which can be
accessed by the callback_fn. The callback_fn signature might be
different for different maps. For example, for hash/array maps,
the signature is
  long callback_fn(map, key, val, callback_ctx)

In the rest of series, Patches 1/2/3/4 did some refactoring. Patch 5
implemented core kernel support for the helper. Patches 6 and 7
added hashmap and arraymap support. Patches 8/9 added libbpf
support. Patch 10 added bpftool support. Patches 11 and 12 added
selftests for hashmap and arraymap.

[1]: https://lore.kernel.org/bpf/20210122205415.113822-1-xiyou.wangcong@gmail.com/

Changelogs:
  v3 -> v4:
    - better refactoring of check_func_call(), calculate subprogno outside
      of __check_func_call() helper. (Andrii)
    - better documentation (like the list of supported maps and their
      callback signatures) in uapi header. (Andrii)
    - implement and use ASSERT_LT in selftests. (Andrii)
    - a few other minor changes.
  v2 -> v3:
    - add comments in retrieve_ptr_limit(), which is in sanitize_ptr_alu(),
      to clarify the code is not executed for PTR_TO_MAP_KEY handling,
      but code is manually tested. (Alexei)
    - require BTF for callback function. (Alexei)
    - simplify hashmap/arraymap callback return handling as return value
      [0, 1] has been enforced by the verifier. (Alexei)
    - also mark global subprog (if used in ld_imm64) as RELO_SUBPROG_ADDR. (Andrii)
    - handle the condition to mark RELO_SUBPROG_ADDR properly. (Andrii)
    - make bpftool subprog insn offset dumping consist with pcrel calls. (Andrii)
  v1 -> v2:
    - setup callee frame in check_helper_call() and then proceed to verify
      helper return value as normal (Alexei)
    - use meta data to keep track of map/func pointer to avoid hard coding
      the register number (Alexei)
    - verify callback_fn return value range [0, 1]. (Alexei)
    - add migrate_{disable, enable} to ensure percpu value is the one
      bpf program expects to see. (Alexei)
    - change bpf_for_each_map_elem() return value to the number of iterated
      elements. (Andrii)
    - Change libbpf pseudo_func relo name to RELO_SUBPROG_ADDR and use
      more rigid checking for the relocation. (Andrii)
    - Better format to print out subprog address with bpftool. (Andrii)
    - Use bpf_prog_test_run to trigger bpf run, instead of bpf_iter. (Andrii)
    - Other misc changes.

Yonghong Song (12):
  bpf: factor out visit_func_call_insn() in check_cfg()
  bpf: factor out verbose_invalid_scalar()
  bpf: refactor check_func_call() to allow callback function
  bpf: change return value of verifier function add_subprog()
  bpf: add bpf_for_each_map_elem() helper
  bpf: add hashtab support for bpf_for_each_map_elem() helper
  bpf: add arraymap support for bpf_for_each_map_elem() helper
  libbpf: move function is_ldimm64() earlier in libbpf.c
  libbpf: support subprog address relocation
  bpftool: print subprog address properly
  selftests/bpf: add hashmap test for bpf_for_each_map_elem() helper
  selftests/bpf: add arraymap test for bpf_for_each_map_elem() helper

 include/linux/bpf.h                           |  17 +
 include/linux/bpf_verifier.h                  |   3 +
 include/uapi/linux/bpf.h                      |  39 +-
 kernel/bpf/arraymap.c                         |  40 ++
 kernel/bpf/bpf_iter.c                         |  16 +
 kernel/bpf/hashtab.c                          |  65 ++++
 kernel/bpf/helpers.c                          |   2 +
 kernel/bpf/verifier.c                         | 364 +++++++++++++++---
 kernel/trace/bpf_trace.c                      |   2 +
 tools/bpf/bpftool/xlated_dumper.c             |   3 +
 tools/include/uapi/linux/bpf.h                |  39 +-
 tools/lib/bpf/libbpf.c                        |  76 +++-
 .../selftests/bpf/prog_tests/for_each.c       | 130 +++++++
 .../bpf/progs/for_each_array_map_elem.c       |  61 +++
 .../bpf/progs/for_each_hash_map_elem.c        |  95 +++++
 tools/testing/selftests/bpf/test_progs.h      |  11 +
 16 files changed, 897 insertions(+), 66 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/for_each.c
 create mode 100644 tools/testing/selftests/bpf/progs/for_each_array_map_elem.c
 create mode 100644 tools/testing/selftests/bpf/progs/for_each_hash_map_elem.c

-- 
2.24.1