[bpf-next,v5,00/12] Support kernel module function calls from eBPF

Message

Kumar Kartikeya Dwivedi Sept. 27, 2021, 2:59 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:
----------
v4 -> v5
v4: https://lore.kernel.org/bpf/[e-mail]

 * Address comments from Alexei
   * Use reserved fd_array area in loader map instead of creating a new map
   * Drop selftest testing the 256 kfunc limit, however selftest testing reuse
     of BTF fd for same kfunc in gen_loader and libbpf is kept
 * Address comments from Andrii
   * Make --no-fail the default for resolve_btfids, i.e. only fail if we find
     BTF section and cannot process it
   * Use obj->btf_modules array to store index in the fd_array, so that we don't
     have to do any searching to reuse the index, instead only set it the first
     time a module BTF's fd is used
   * Make find_ksym_btf_id to return struct module_btf * in last parameter
   * Improve logging when index becomes bigger than INT16_MAX
   * Add btf__find_by_name_kind_own internal helper to only start searching for
     kfunc ID in module BTF, since find_ksym_btf_id already checks vmlinux BTF
     before iterating over module BTFs.
   * Fix various other nits
 * Fixes for failing selftests on BPF CI
 * Rearrange/cleanup selftests
   * Avoid testing kfunc limit (Alexei)
   * Do test gen_loader and libbpf BTF fd index dedup with 256 calls
   * Move invalid kfunc failure test to verifier selftest
   * Minimize duplication
 * Use consistent bpf_check_<type>_kfunc_call naming for module kfunc callback
 * Since we try to add fd using add_data while we can, cherry pick Alexei's
   patch from CO-RE RFC series to align gen_loader data.

v3 -> v4
v3: https://lore.kernel.org/bpf/[e-mail]

 * Address comments from Alexei
   * Drop MAX_BPF_STACK change, instead move map_fd and BTF fd to BPF array map
     and pass fd_array using BPF_PSEUDO_MAP_IDX_VALUE
 * Address comments from Andrii
   * Fix selftest to store to variable for observing function call instead of
     printk and polluting CI logs
 * Drop use of raw_tp for testing, instead reuse classifier based prog_test_run
 * Drop index + 1 based insn->off convention for kfunc module calls
 * Expand selftests to cover more corner cases
 * Misc cleanups

v2 -> v3
v2: https://lore.kernel.org/bpf/[e-mail]

 * Fix issues pointed out by Kernel Test Robot
 * Fix find_kfunc_desc to also take offset into consideration when comparing

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

Alexei Starovoitov (1):
  libbpf: Make gen_loader data aligned.

Kumar Kartikeya Dwivedi (11):
  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
  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
  libbpf: Fix skel_internal.h to set errno on loader retval < 0
  bpf: selftests: Fix fd cleanup in get_branch_snapshot
  bpf: selftests: Add selftests for module kfunc support

 include/linux/bpf.h                           |   8 +-
 include/linux/bpf_verifier.h                  |   2 +
 include/linux/bpfptr.h                        |   1 +
 include/linux/btf.h                           |  37 +++
 kernel/bpf/btf.c                              |  56 ++++
 kernel/bpf/core.c                             |   4 +
 kernel/bpf/verifier.c                         | 220 +++++++++++++--
 net/bpf/test_run.c                            |   7 +-
 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               |  28 +-
 tools/lib/bpf/bpf.c                           |   1 +
 tools/lib/bpf/bpf_gen_internal.h              |  14 +-
 tools/lib/bpf/btf.c                           |  19 +-
 tools/lib/bpf/gen_loader.c                    | 250 +++++++++++++++---
 tools/lib/bpf/libbpf.c                        | 110 +++++---
 tools/lib/bpf/libbpf_internal.h               |   3 +
 tools/lib/bpf/skel_internal.h                 |   6 +-
 tools/testing/selftests/bpf/Makefile          |  10 +-
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  23 +-
 .../bpf/prog_tests/get_branch_snapshot.c      |   5 +-
 .../selftests/bpf/prog_tests/ksyms_module.c   |  29 +-
 .../bpf/prog_tests/ksyms_module_libbpf.c      |  28 ++
 .../selftests/bpf/progs/test_ksyms_module.c   |  46 +++-
 tools/testing/selftests/bpf/verifier/calls.c  |  23 ++
 28 files changed, 860 insertions(+), 187 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/ksyms_module_libbpf.c