[bpf-next,v2,00/10] Support kernel module function calls from eBPF

Message

Kumar Kartikeya Dwivedi Sept. 14, 2021, 12:37 p.m. UTC

This set enables kernel module function calls, and also modifies verifier logic
to permit invalid kernel function calls as long as they are pruned as part of
dead code elimination. This is done to provide better runtime portability for
BPF objects, which can conditionally disable parts of code that are pruned later
by the verifier (e.g. const volatile vars, kconfig options). libbpf
modifications are made along with kernel changes to support module function
calls. The set includes gen_loader support for emitting kfunc relocations.

It also converts TCP congestion control objects to use the module kfunc support
instead of relying on IS_BUILTIN ifdef.

Changelog:
----------
RFC v1 -> v2
v1: https://lore.kernel.org/bpf/[e-mail]

 * Address comments from Alexei
   * Reuse fd_array instead of introducing kfunc_btf_fds array
   * Take btf and module reference as needed, instead of preloading
   * Add BTF_KIND_FUNC relocation support to gen_loader infrastructure
 * Address comments from Andrii
   * Drop hashmap in libbpf for finding index of existing BTF in fd_array
   * Preserve invalid kfunc calls only when the symbol is weak
 * Adjust verifier selftests

Kumar Kartikeya Dwivedi (10):
  bpf: Introduce BPF support for kernel module function calls
  bpf: Be conservative while processing invalid kfunc calls
  bpf: btf: Introduce helpers for dynamic BTF set registration
  tools: Allow specifying base BTF file in resolve_btfids
  bpf: Enable TCP congestion control kfunc from modules
  bpf: Bump MAX_BPF_STACK size to 768 bytes
  libbpf: Support kernel module function calls
  libbpf: Resolve invalid weak kfunc calls with imm = 0, off = 0
  libbpf: Update gen_loader to emit BTF_KIND_FUNC relocations
  bpf, selftests: Add basic test for module kfunc call

 include/linux/bpf.h                           |   8 +-
 include/linux/bpf_verifier.h                  |   2 +
 include/linux/bpfptr.h                        |   1 +
 include/linux/btf.h                           |  38 ++++
 include/linux/filter.h                        |   4 +-
 kernel/bpf/btf.c                              |  56 +++++
 kernel/bpf/core.c                             |   2 +
 kernel/bpf/verifier.c                         | 200 ++++++++++++++++--
 kernel/trace/bpf_trace.c                      |   1 +
 net/bpf/test_run.c                            |   2 +-
 net/ipv4/bpf_tcp_ca.c                         |  36 +---
 net/ipv4/tcp_bbr.c                            |  28 ++-
 net/ipv4/tcp_cubic.c                          |  26 ++-
 net/ipv4/tcp_dctcp.c                          |  26 ++-
 scripts/Makefile.modfinal                     |   1 +
 tools/bpf/resolve_btfids/main.c               |  19 +-
 tools/lib/bpf/bpf.c                           |   1 +
 tools/lib/bpf/bpf_gen_internal.h              |  12 +-
 tools/lib/bpf/gen_loader.c                    |  93 +++++++-
 tools/lib/bpf/libbpf.c                        |  81 +++++--
 tools/lib/bpf/libbpf_internal.h               |   1 +
 tools/testing/selftests/bpf/Makefile          |   1 +
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  23 +-
 .../selftests/bpf/prog_tests/ksyms_module.c   |  13 +-
 .../bpf/prog_tests/ksyms_module_libbpf.c      |  18 ++
 .../selftests/bpf/progs/test_ksyms_module.c   |   9 +
 .../bpf/progs/test_ksyms_module_libbpf.c      |  35 +++
 tools/testing/selftests/bpf/verifier/calls.c  |  22 +-
 .../selftests/bpf/verifier/raw_stack.c        |   4 +-
 .../selftests/bpf/verifier/stack_ptr.c        |   6 +-
 .../testing/selftests/bpf/verifier/var_off.c  |   4 +-
 31 files changed, 661 insertions(+), 112 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/ksyms_module_libbpf.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_ksyms_module_libbpf.c