From: Alexei Starovoitov <ast@xxxxxxxxxx>
Hi All,
This is very early RFC that introduces CO-RE support in the kernel.
There are several reasons to add such support:
1. It's a step toward signed BPF programs.
2. It allows golang like languages that struggle to adopt libbpf
to take advantage of CO-RE powers.
3. Currently the field accessed by 'ldx [R1 + 10]' insn is recognized
by the verifier purely based on +10 offset. If R1 points to a union
the verifier picks one of the fields at this offset.
With CO-RE the kernel can disambiguate the field access.
This set wires all relevant pieces and passes two selftests with CO-RE
in the kernel.
The main goal of RFC is to get feedback on patch 3.
It's passing CO-RE relocation into the kernel via bpf_core_apply_relo()
helper that is called by the loader program.
It works, but there is no clean way to add error reporting here.
So I'm thinking that the better approach would be to pass an array
of 'struct bpf_core_relo_desc' into PROG_LOAD command similar to
how func_info and line_info are passed.
Such approach would allow for the use case 3 above (which
current approach in patch 3 doesn't support).
Major TODOs:
- rename kernel btf_*() helpers to match libbpf btf_*() helpers
to avoid equivalent helpers in patch 1.
- bpf_core_match_member() in relo_core.c is recursive.
Limit its recursion or refactor.
- implemented bpf_core_types_are_compat(). duh.
- decide whether bpf_core_find_cands() needs hash table (like libbpf does)
or not.
Alexei Starovoitov (10):
bpf: Prepare relo_core.c for kernel duty.
bpf: Define enum bpf_core_relo_kind as uapi.
bpf: Add proto of bpf_core_apply_relo()
bpf: Add bpf_core_add_cands() and wire it into
bpf_core_apply_relo_insn().
libbpf: Use CO-RE in the kernel in light skeleton.
libbpf: Make gen_loader data aligned.
libbpf: Support init of inner maps in light skeleton.
selftests/bpf: Convert kfunc test with CO-RE to lskel.
selftests/bpf: Improve inner_map test coverage.
selftests/bpf: Convert map_ptr_kern test to use light skeleton.
include/linux/bpf.h | 1 +
include/linux/btf.h | 89 ++++++++
include/uapi/linux/bpf.h | 33 +++
kernel/bpf/Makefile | 4 +
kernel/bpf/btf.c | 193 ++++++++++++++++++
kernel/bpf/syscall.c | 2 +
tools/include/uapi/linux/bpf.h | 33 +++
tools/lib/bpf/bpf_gen_internal.h | 13 ++
tools/lib/bpf/gen_loader.c | 85 +++++++-
tools/lib/bpf/libbpf.c | 35 +++-
tools/lib/bpf/relo_core.c | 156 ++++++++++----
tools/lib/bpf/relo_core.h | 18 --
tools/testing/selftests/bpf/Makefile | 2 +-
.../selftests/bpf/prog_tests/kfunc_call.c | 4 +-
.../selftests/bpf/prog_tests/map_ptr.c | 8 +-
.../selftests/bpf/progs/map_ptr_kern.c | 16 +-
16 files changed, 611 insertions(+), 81 deletions(-)
--
2.30.2
