[PATCH RFC bpf-next 0/4] Support kernel module ksym variables

[Andrii Nakryiko <andrii@kernel.org>]

This RFC is sent to show how ksym variable access in BPF program can be
supported for kernel modules and gather some feedback while necessary fixes
for pahole ([0]) are reviewed and hopefully will make it into 1.20 version.

This work builds on all the previous kernel and libbpf changes to support
kernel module BTFs. On top of that, BPF verifier will now support ldimm64 with
src_reg=BPF_PSEUDO_BTF_ID and non-zero insn[1].imm field, which contains BTF
FD for kernel module. In such case, used module BTF, similarly to used BPF
map, will be recorded and refcnt will be increased for both BTF object itself
and its kernel module. This makes sure kernel module won't be unloaded from
under active attached BPF program.

New selftest validates all this is working as intended. bpf_testmod.ko is
extended with per-CPU variable.

  [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=400229&state=*

Andrii Nakryiko (4):
  selftests/bpf: sync RCU before unloading bpf_testmod
  bpf: support BPF ksym variables in kernel modules
  libbpf: support kernel module ksym externs
  selftests/bpf: test kernel module ksym externs

 include/linux/bpf.h                           |   9 ++
 include/linux/bpf_verifier.h                  |   3 +
 include/linux/btf.h                           |   3 +
 kernel/bpf/btf.c                              |  31 +++-
 kernel/bpf/core.c                             |  23 +++
 kernel/bpf/verifier.c                         | 149 ++++++++++++++----
 tools/lib/bpf/libbpf.c                        |  47 ++++--
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |   3 +
 .../selftests/bpf/prog_tests/btf_map_in_map.c |  33 ----
 .../selftests/bpf/prog_tests/ksyms_module.c   |  33 ++++
 .../selftests/bpf/progs/test_ksyms_module.c   |  26 +++
 tools/testing/selftests/bpf/test_progs.c      |  40 +++++
 tools/testing/selftests/bpf/test_progs.h      |   1 +
 13 files changed, 321 insertions(+), 80 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/ksyms_module.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_ksyms_module.c

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2.24.1