[RFC,bpf-next,0/6] bpf: Add gen_epilogue and allow kfunc call in pro/epilogue

Message

Martin KaFai Lau Aug. 13, 2024, 6:49 p.m. UTC

From: Martin KaFai Lau <[e-mail]>

This set allows the subsystem to patch codes before BPF_EXIT.
The verifier ops, .gen_epilogue, is added for this purpose.
One of the use case will be in the bpf qdisc, the bpf qdisc
subsystem can ensure the skb->dev is in the correct value.
The bpf qdisc subsystem can either inline fixing it in the
epilogue or call another kfunc to handle (e.g. drop) it in
the epilogue. Another use case could be in bpf_tcp_ca.c to
enforce snd_cwnd has sane value (e.g. non zero).

The existing .gen_prologue can call bpf helper.
This set also allows the existing .gen_prologue and the new
.gen_epilogue to call kfunc. Other than the skb drop
mentioned above, the bpf qdisc subsystem can call
kfunc to enforce initializing / releasing resources (e.g.
qdisc_watchdog_init/cancel) in some of the qdisc_ops.

It is under RFC because the .gen_epilogue will need 8 extra
bytes in the stack to save the ctx pointer. It is now
done after the check_max_stack_depth. The ctx pointer
saving will need to be done earlier before check_max_stack_depth.

Martin KaFai Lau (6):
  bpf: Add gen_epilogue to bpf_verifier_ops
  bpf: Export bpf_base_func_proto
  selftests/test: test gen_prologue and gen_epilogue
  bpf: Add module parameter to gen_prologue and gen_epilogue
  bpf: Allow pro/epilogue to call kfunc
  selftests/bpf: Add kfunc call test in gen_prologue and gen_epilogue

 include/linux/bpf.h                           |   4 +-
 include/linux/btf.h                           |   1 +
 kernel/bpf/btf.c                              |   2 +-
 kernel/bpf/cgroup.c                           |   3 +-
 kernel/bpf/helpers.c                          |   1 +
 kernel/bpf/verifier.c                         | 146 ++++++++++-
 net/core/filter.c                             |   6 +-
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   | 228 ++++++++++++++++++
 .../selftests/bpf/bpf_testmod/bpf_testmod.h   |  11 +
 .../bpf/bpf_testmod/bpf_testmod_kfunc.h       |   6 +
 .../bpf/prog_tests/struct_ops_syscall.c       |  92 +++++++
 .../selftests/bpf/progs/struct_ops_syscall.c  | 113 +++++++++
 12 files changed, 604 insertions(+), 9 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/struct_ops_syscall.c
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_syscall.c