[PATCH v2 bpf-next 00/14] bpf: Support calling kernel function

[Martin KaFai Lau <kafai@fb.com>]

This series adds support to allow bpf program calling kernel function.

The use case included in this set is to allow bpf-tcp-cc to directly
call some tcp-cc helper functions (e.g. "tcp_cong_avoid_ai()").  Those
functions have already been used by some kernel tcp-cc implementations.

This set will also allow the bpf-tcp-cc program to directly call the
kernel tcp-cc implementation,  For example, a bpf_dctcp may only want to
implement its own dctcp_cwnd_event() and reuse other dctcp_*() directly
from the kernel tcp_dctcp.c instead of reimplementing (or
copy-and-pasting) them.

The tcp-cc kernel functions mentioned above will be white listed
for the struct_ops bpf-tcp-cc programs to use in a later patch.
The white listed functions are not bounded to a fixed ABI contract.
Those functions have already been used by the existing kernel tcp-cc.
If any of them has changed, both in-tree and out-of-tree kernel tcp-cc
implementations have to be changed.  The same goes for the struct_ops
bpf-tcp-cc programs which have to be adjusted accordingly.

Please see individual patch for details.

v2:
- Patch 2 in v1 is removed.  No need to support extern func in kernel.
  Changed libbpf to adjust the .ksyms datasec for extern func
  in patch 11. (Andrii)
- Name change: btf_check_func_arg_match() and btf_check_subprog_arg_match()
  in patch 2. (Andrii)
- Always set unreliable on any error in patch 2 since it does not
  matter. (Andrii)
- s/kern_func/kfunc/ and s/descriptor/desc/ in this set. (Andrii)
- Remove some unnecessary changes in disasm.h and disasm.c
  in patch 3.  In particular, no need to change the function
  signature in bpf_insn_revmap_call_t.  Also, removed the changes
  in print_bpf_insn().
- Fixed an issue in check_kfunc_call() when the calling kernel function
  returns a pointer in patch 3.  Added a selftest.
- Adjusted the verifier selftests due to the changes in the verifier log
  in patch 3.
- Fixed a comparison issue in kfunc_desc_cmp_by_imm() in patch 3. (Andrii)
- Name change: is_ldimm64_insn(),
  new helper: is_call_insn() in patch 10 (Andrii)
- Move btf_func_linkage() from btf.h to libbpf.c in patch 11. (Andrii)
- Fixed the linker error when CONFIG_BPF_SYSCALL is not defined.
  Moved the check_kfunc_call from filter.c to test_run.c in patch 14.
  (kernel test robot)

Martin KaFai Lau (14):
  bpf: Simplify freeing logic in linfo and jited_linfo
  bpf: Refactor btf_check_func_arg_match
  bpf: Support bpf program calling kernel function
  bpf: Support kernel function call in x86-32
  tcp: Rename bictcp function prefix to cubictcp
  bpf: tcp: Put some tcp cong functions in allowlist for bpf-tcp-cc
  libbpf: Refactor bpf_object__resolve_ksyms_btf_id
  libbpf: Refactor codes for finding btf id of a kernel symbol
  libbpf: Rename RELO_EXTERN to RELO_EXTERN_VAR
  libbpf: Record extern sym relocation first
  libbpf: Support extern kernel function
  bpf: selftests: Rename bictcp to bpf_cubic
  bpf: selftests: bpf_cubic and bpf_dctcp calling kernel functions
  bpf: selftests: Add kfunc_call test

 arch/x86/net/bpf_jit_comp.c                   |   5 +
 arch/x86/net/bpf_jit_comp32.c                 | 198 +++++++++
 include/linux/bpf.h                           |  34 +-
 include/linux/btf.h                           |   6 +
 include/linux/filter.h                        |   4 +-
 include/uapi/linux/bpf.h                      |   4 +
 kernel/bpf/btf.c                              | 218 ++++++----
 kernel/bpf/core.c                             |  47 +--
 kernel/bpf/disasm.c                           |  13 +-
 kernel/bpf/syscall.c                          |   4 +-
 kernel/bpf/verifier.c                         | 376 +++++++++++++++--
 net/bpf/test_run.c                            |  28 ++
 net/core/filter.c                             |   1 +
 net/ipv4/bpf_tcp_ca.c                         |  41 ++
 net/ipv4/tcp_cubic.c                          |  24 +-
 tools/include/uapi/linux/bpf.h                |   4 +
 tools/lib/bpf/libbpf.c                        | 389 +++++++++++++-----
 tools/testing/selftests/bpf/bpf_tcp_helpers.h |  29 +-
 .../selftests/bpf/prog_tests/kfunc_call.c     |  59 +++
 tools/testing/selftests/bpf/progs/bpf_cubic.c |  36 +-
 tools/testing/selftests/bpf/progs/bpf_dctcp.c |  22 +-
 .../selftests/bpf/progs/kfunc_call_test.c     |  47 +++
 .../bpf/progs/kfunc_call_test_subprog.c       |  42 ++
 tools/testing/selftests/bpf/verifier/calls.c  |  12 +-
 .../selftests/bpf/verifier/dead_code.c        |  10 +-
 25 files changed, 1334 insertions(+), 319 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/kfunc_call.c
 create mode 100644 tools/testing/selftests/bpf/progs/kfunc_call_test.c
 create mode 100644 tools/testing/selftests/bpf/progs/kfunc_call_test_subprog.c

-- 
2.30.2