[RFC,bpf-next,0/5] static branches

Message

Anton Protopopov Jan. 22, 2024, 4:49 p.m. UTC

This series adds support for mapping between xlated and original
instructions offsets, mapping between xlated and jitted instructions
offsets (x86), support for two new BPF instruction JA[SRC=1] and
JA[SRC=3], and a new syscall to configure the jitted values of such
instructions.

This a follow up to the previous attempt to add static keys support
(see [1], [2]) which implements lower-level functionality than what
was proposed before.

It's RFC because 1) to run self-tests it requires a patched llvm
(https://github.com/llvm/llvm-project/pull/75110, thanks a lot
Yonghong!) 2) before spending time writing selftests and proper
bpftool updates [this time] I would prefer to get some initial
feedback first (for examples, see below)

The first patch is a formal fix.
The second patch adds xlated -> original mapping.
The third patch adds xlated -> jitted mapping.
The fourth patch adds support for new instructions.
And the fifth patch adds support for new syscall.

Altogether this provides enough functionality to dynamically patch
programs and support simple static keys. See the third patch which
displays an example of mappings between xlated->orig, xlated->jited.
See the last patch which includes description of how to implement
simple static key functionality.

This would be also interesting to hear what people think about more
high-level api where one "key" controls a set of static branches in
multiple programs and can serialize access to all the branches. What
kind of BPF object can represent such functionality, besides a map,
if any?

  [1] https://lpc.events/event/17/contributions/1608/attachments/1278/2578/bpf-static-keys.pdf
  [2] https://lore.kernel.org/bpf/[e-mail]/

Anton Protopopov (5):
  bpf: fix potential error return
  bpf: keep track of and expose xlated insn offsets
  bpf: x86: expose how xlated insns map to jitted insns
  bpf: add support for an extended JA instruction
  bpf: x86: add BPF_STATIC_BRANCH_UPDATE syscall

 arch/x86/net/bpf_jit_comp.c       |  71 ++++++++++++++++++-
 include/linux/bpf.h               |  11 +++
 include/linux/bpf_verifier.h      |   1 -
 include/linux/filter.h            |   1 +
 include/uapi/linux/bpf.h          |  26 +++++++
 kernel/bpf/core.c                 |  69 +++++++++++++++++-
 kernel/bpf/syscall.c              | 112 ++++++++++++++++++++++++++++++
 kernel/bpf/verifier.c             |  58 ++++++++++++----
 tools/bpf/bpftool/prog.c          |  14 ++++
 tools/bpf/bpftool/xlated_dumper.c |   2 +-
 tools/bpf/bpftool/xlated_dumper.h |   2 +
 tools/include/uapi/linux/bpf.h    |  26 +++++++
 12 files changed, 375 insertions(+), 18 deletions(-)