Various locking issues are possible with bpf_ktime_get_coarse_ns() and bpf_timer_* set of helpers. syzbot found a locking issue with bpf_ktime_get_coarse_ns() helper executed in BPF_PROG_TYPE_PERF_EVENT prog type - [1]. The issue is possible because the helper uses non fast version of time accessor that isn't safe for any context. The helper was added because it provided performance benefits in comparison to bpf_ktime_get_ns() helper. A similar locking issue is possible with bpf_timer_* set of helpers when used in tracing progs. The solution is to restrict use of the helpers in tracing progs. In the [1] discussion it was stated that bpf_spin_lock related helpers shall also be excluded for tracing progs. The verifier has a compatibility check between a map and a program. If a tracing program tries to use a map which value has struct bpf_spin_lock the verifier fails that is why bpf_spin_lock is already restricted. Patch 1 restricts helpers Patch 2 adds tests v1 -> v2: * Limit the helpers via func proto getters instead of allowed callback * Add note about helpers' restrictions to linux/bpf.h * Add Fixes tag * Remove extra \0 from btf_str_sec * Beside asm tests add prog tests * Trim CC 1. https://lore.kernel.org/all/00000000000013aebd05cff8e064@xxxxxxxxxx/ Dmitrii Banshchikov (2): bpf: Forbid bpf_ktime_get_coarse_ns and bpf_timer_* in tracing progs selftests/bpf: Add tests for restricted helpers include/uapi/linux/bpf.h | 6 + kernel/bpf/cgroup.c | 2 + kernel/bpf/helpers.c | 2 - kernel/bpf/verifier.c | 7 + kernel/trace/bpf_trace.c | 2 - net/core/filter.c | 6 + net/ipv4/bpf_tcp_ca.c | 2 + tools/include/uapi/linux/bpf.h | 6 + .../bpf/prog_tests/helper_restricted.c | 33 +++ .../bpf/progs/test_helper_restricted.c | 123 +++++++++++ tools/testing/selftests/bpf/test_verifier.c | 46 +++- .../bpf/verifier/helper_restricted.c | 196 ++++++++++++++++++ 12 files changed, 426 insertions(+), 5 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/helper_restricted.c create mode 100644 tools/testing/selftests/bpf/progs/test_helper_restricted.c create mode 100644 tools/testing/selftests/bpf/verifier/helper_restricted.c -- 2.25.1
