bpf: Cleanup check_refcount_ok

Browse source

Discussion around a recently-submitted patch provided historical
context for check_refcount_ok [0]. Specifically, the function and its
helpers - may_be_acquire_function and arg_type_may_be_refcounted -
predate the OBJ_RELEASE type flag and the addition of many more helpers
with acquire/release semantics.

The purpose of check_refcount_ok is to ensure:
  1) Helper doesn't have multiple uses of return reg's ref_obj_id
  2) Helper with release semantics only has one arg needing to be
  released, since that's tracked using meta->ref_obj_id

With current verifier, it's safe to remove check_refcount_ok and its
helpers. Since addition of OBJ_RELEASE type flag, case 2) has been
handled by the arg_type_is_release check in check_func_arg. To ensure
case 1) won't result in verifier silently prioritizing one use of
ref_obj_id, this patch adds a helper_multiple_ref_obj_use check which
fails loudly if a helper passes > 1 test for use of ref_obj_id.

  [0]: lore.kernel.org/bpf/20220713234529.4154673-1-davemarchevsky@fb.com

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Joanne Koong <joannelkoong@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220808171559.3251090-1-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

...

This commit is contained in:

Dave Marchevsky 2022-08-08 10:15:59 -07:00 • committed by Alexei Starovoitov

parent 6e116280b4

commit b2d8ef19c6

1 changed files with 29 additions and 45 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

74

kernel/bpf/verifier.c

View file