[PATCH RFC bpf-next v2 0/4] bpf: Support 64-bit pointers to kfuncs

[Ilya Leoshkevich <iii@linux.ibm.com>]

v1: https://lore.kernel.org/bpf/20230214212809.242632-1-iii@linux.ibm.com/T/#t
v1 -> v2: Add BPF_HELPER_CALL (Stanislav).
          Add check_subprogs() cleanup - noticed while reviewing the
          code for BPF_HELPER_CALL.
          Drop WARN_ON_ONCE (Stanislav, Alexei).
          Add bpf_jit_get_func_addr() to x86_64 JIT.

Hi,

This series solves the problems outlined in [1, 2, 3]. The main problem
is that kfuncs in modules do not fit into bpf_insn.imm on s390x; the
secondary problem is that there is a conflict between "abstract" XDP
metadata function BTF ids and their "concrete" addresses.

The solution is to keep fkunc BTF ids in bpf_insn.imm, and put the
addresses into bpf_kfunc_desc, which does not have size restrictions.

Regtested with test_verifier and test_progs on x86_64 and s390x.
TODO: Need to add bpf_jit_get_func_addr() to arm, sparc and i386 JITs.

[1] https://lore.kernel.org/bpf/Y9%2FyrKZkBK6yzXp+@krava/
[2] https://lore.kernel.org/bpf/20230128000650.1516334-1-iii@linux.ibm.com/
[3] https://lore.kernel.org/bpf/20230128000650.1516334-32-iii@linux.ibm.com/

Best regards,
Ilya

Ilya Leoshkevich (4):
  bpf: Introduce BPF_HELPER_CALL
  bpf: Use BPF_HELPER_CALL in check_subprogs()
  bpf, x86: Use bpf_jit_get_func_addr()
  bpf: Support 64-bit pointers to kfuncs

 arch/x86/net/bpf_jit_comp.c    | 15 ++++--
 include/linux/bpf.h            |  2 +
 include/uapi/linux/bpf.h       |  4 ++
 kernel/bpf/core.c              | 21 ++++++--
 kernel/bpf/disasm.c            |  2 +-
 kernel/bpf/verifier.c          | 95 ++++++++++++----------------------
 tools/include/linux/filter.h   |  2 +-
 tools/include/uapi/linux/bpf.h |  4 ++
 8 files changed, 75 insertions(+), 70 deletions(-)

-- 
2.39.1