[PATCH bpf-next 0/4] destructive bpf kfuncs (was: bpf_panic)

[Artem Savkov <asavkov@redhat.com>]

eBPF is often used for kernel debugging, and one of the widely used and
powerful debugging techniques is post-mortem debugging with a full memory dump.
Triggering a panic at exactly the right moment allows the user to get such a
dump and thus a better view at the system's state. Right now the only way to
do this in BPF is to signal userspace to trigger kexec/panic. This is
suboptimal as going through userspace requires context changes and adds
significant delays taking system further away from "the right moment". On a
single-cpu system the situation is even worse because BPF program won't even be
able to block the thread of interest.

This patchset tries to solve this problem by allowing properly marked tracing
bpf programs to call crash_kexec() kernel function.

This is a continuation of bpf_panic patchset with initial feedback taken into
account.

Changes from RFC:
 - sysctl knob dropped
 - using crash_kexec() instead of panic()
 - using kfuncs instead of adding a new helper

Artem Savkov (4):
  bpf: add BPF_F_DESTRUCTIVE flag for BPF_PROG_LOAD
  bpf: add destructive kfunc set
  selftests/bpf: add destructive kfunc tests
  bpf: export crash_kexec() as destructive kfunc

 include/linux/bpf.h                           |  1 +
 include/linux/btf.h                           |  2 +
 include/uapi/linux/bpf.h                      |  6 +++
 kernel/bpf/syscall.c                          |  4 +-
 kernel/bpf/verifier.c                         | 12 ++++++
 kernel/kexec_core.c                           | 22 ++++++++++
 net/bpf/test_run.c                            | 12 +++++-
 tools/include/uapi/linux/bpf.h                |  6 +++
 .../selftests/bpf/prog_tests/kfunc_call.c     | 41 +++++++++++++++++++
 .../bpf/progs/kfunc_call_destructive.c        | 14 +++++++
 10 files changed, 118 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/kfunc_call_destructive.c

-- 
2.35.3