[v2,bpf-next,0/7] Support kernel module ksym variables

Message

Andrii Nakryiko Jan. 8, 2021, 10:09 p.m. UTC

Add support for using kernel module global variables (__ksym externs in BPF
program). BPF verifier will now support ldimm64 with src_reg=BPF_PSEUDO_BTF_ID
and non-zero insn[1].imm field, specifying module BTF's FD. In such case,
module BTF object, similarly to BPF maps referenced from ldimm64 with
src_reg=BPF_PSEUDO_MAP_FD, will be recorded in bpf_progran's auxiliary data
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. These refcounts will be dropped when BPF program is unloaded.

New selftest validates all this is working as intended. bpf_testmod.ko is
extended with per-CPU variable. Selftests expects the latest pahole changes
(soon to be released as v1.20) to generate per-CPU variable BTF info for
kernel module.

v1->v2:
  - fixed few compiler warnings, posted as separate pre-patches;
rfc->v1:
  - use sys_membarrier(MEMBARRIER_CMD_GLOBAL) (Alexei).

Cc: Hao Luo <[e-mail]>
Andrii Nakryiko (7):
  bpf: add bpf_patch_call_args prototype to include/linux/bpf.h
  bpf: avoid warning when re-casting __bpf_call_base into
    __bpf_call_base_args
  bpf: declare __bpf_free_used_maps() unconditionally
  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                           |  18 ++-
 include/linux/bpf_verifier.h                  |   3 +
 include/linux/btf.h                           |   3 +
 include/linux/filter.h                        |   2 +-
 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      |  11 ++
 tools/testing/selftests/bpf/test_progs.h      |   1 +
 14 files changed, 300 insertions(+), 83 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