The verifier currently has a hard-coded allowlist of kfuncs that may be called while a BPF program holds a bpf_spin_lock. This works for the small set of built-in kfuncs known to the verifier, but it does not give kfunc providers a registration-time way to declare that a kfunc is safe in such a region. In particular, module kfuncs cannot be added to that allowlist without changing verifier code.
This series adds a new KF_SPINLOCK_SAFE kfunc flag and teaches the verifier to use kfunc registration metadata when deciding whether a kfunc call is allowed while a bpf_spin_lock is held. The built-in kfuncs that are currently accepted by the verifier's lock-held allowlist are annotated with the new flag. This preserves the existing behavior while removing the verifier-side category checks and uses the same mechanism for built-in and module kfuncs. The selftest coverage marks one bpf_testmod kfunc as KF_SPINLOCK_SAFE and verifies that it can be called under a bpf_spin_lock. It also calls another registered but unmarked bpf_testmod kfunc under the lock and checks that the verifier rejects it. Changes in v2: - Rename KF_SPIN_LOCK to KF_SPINLOCK_SAFE. (Kumar Kartikeya Dwivedi, Leon Hwang) - Deprecate the verifier's lock-held allowlist mechanism and annotate the relevant kfuncs uniformly with KF_SPINLOCK_SAFE (Kumar Kartikeya Dwivedi) - Add selftests. (Leon Hwang) Link to v1: https://lore.kernel.org/bpf/[email protected]/ Kaitao Cheng (3): bpf: Add KF_SPINLOCK_SAFE flag for kfuncs under bpf_spin_lock bpf: Mark existing lock-safe kfuncs with KF_SPINLOCK_SAFE selftests/bpf: Test module kfunc calls under spin lock include/linux/btf.h | 1 + kernel/bpf/arena.c | 6 +- kernel/bpf/helpers.c | 56 ++++++++++--------- kernel/bpf/rqspinlock.c | 8 +-- kernel/bpf/verifier.c | 38 +++---------- .../selftests/bpf/prog_tests/kfunc_call.c | 2 + .../selftests/bpf/progs/kfunc_call_fail.c | 12 ++++ .../selftests/bpf/progs/kfunc_call_test.c | 12 ++++ .../selftests/bpf/test_kmods/bpf_testmod.c | 2 +- 9 files changed, 72 insertions(+), 65 deletions(-) -- 2.50.1 (Apple Git-155)
