[PATCH RFC bpf-next 0/1] bpf: Support 64-bit pointers to kfuncs

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

Hi,

This is the first attempt to solve 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 proposed 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.

Jiri and I discussed putting them into bpf_insn_aux_data, but at the
very beginning of the implementation it became clear that this struct
is freed at the end of verification and is not available during JITing.

I regtested this only on s390x, where it does not regress anything. If
this approach is fine (especially w.r.t. dev-bound kfuncs), I can check
the other arches.

[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 (1):
  bpf: Support 64-bit pointers to kfuncs

 include/linux/bpf.h   |  2 ++
 kernel/bpf/core.c     | 23 ++++++++++---
 kernel/bpf/verifier.c | 79 +++++++++++++------------------------------
 3 files changed, 45 insertions(+), 59 deletions(-)

-- 
2.39.1