bpf: expose bpf_{g,s}et_retval to more cgroup hooks

Apparently, only a small subset of cgroup hooks actually falls back to cgroup_base_func_proto. This leads to unexpected result where not all cgroup helpers have bpf_{g,s}et_retval.

It's getting harder and harder to manage which helpers are exported to which hooks. We now have the following call chains:

- cg_skb_func_proto
- sk_filter_func_proto
- bpf_sk_base_func_proto
- bpf_base_func_proto

So by looking at cg_skb_func_proto it's pretty hard to understand what's going on.

For cgroup helpers, I'm proposing we do the following instead:

  func_proto = cgroup_common_func_proto();
  if (func_proto) return func_proto;

  /* optional, if hook has 'current' */
  func_proto = cgroup_current_func_proto();
  if (func_proto) return func_proto;

...

  switch (func_id) {
  /* hook specific helpers */
  case BPF_FUNC_hook_specific_helper:
    return &xyz;
  default:
    /* always fall back to plain bpf_base_func_proto */
    bpf_base_func_proto(func_id);
  }

If this turns out more workable, we can follow up with converting the rest to the same pattern.

v5:
- remove net/cls_cgroup.h include from patch 1/5 (Martin)
- move endif changes from patch 1/5 to 3/5 (Martin)
- don't define __weak protos, the ones in core.c suffice (Martin)

v4:
- don't touch existing helper.c helpers (Martin)
- drop unneeded CONFIG_CGROUP_BPF in bpf_lsm_func_proto (Martin)

v3:
- expose strtol/strtoul everywhere (Martin)
- move helpers declarations from bpf.h to bpf-cgroup.h (Martin)
- revise bpf_{g,s}et_retval documentation (Martin)
- don't expose bpf_{g,s}et_retval to cg_skb hooks (Martin)

v2:
- move everything into kernel/bpf/cgroup.c instead (Martin)
- use cgroup_common_func_proto in lsm (Martin)

Stanislav Fomichev (5):
bpf: Introduce cgroup_{common,current}_func_proto
bpf: Use cgroup_{common,current}_func_proto in more hooks
bpf: expose bpf_strtol and bpf_strtoul to all program types
bpf: update bpf_{g,s}et_retval documentation selftests/bpf: Make sure bpf_{g,s}et_retval is exposed everywhere

 include/linux/bpf-cgroup.h                    |  17 ++
 include/linux/bpf.h                           |   1 +
 include/uapi/linux/bpf.h                      |  22 ++-
 kernel/bpf/bpf_lsm.c                          |  17 +-
 kernel/bpf/cgroup.c                           | 157 +++++++++++++++---
 kernel/bpf/helpers.c                          |  40 +----
 net/core/filter.c                             |  80 ++++-----
 tools/include/uapi/linux/bpf.h                |  22 ++-
 tools/testing/selftests/bpf/Makefile          |   1 +
 .../bpf/cgroup_getset_retval_hooks.h          |  25 +++
 .../bpf/prog_tests/cgroup_getset_retval.c     |  48 ++++++
 .../bpf/progs/cgroup_getset_retval_hooks.c    |  16 ++
 12 files changed, 322 insertions(+), 124 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/cgroup_getset_retval_hooks.h
 create mode 100644 tools/testing/selftests/bpf/progs/cgroup_getset_retval_hooks.c

2.37.1.595.g718a3a8f04-goog