On Sat, Nov 13, 2021 at 6:22 AM Dmitrii Banshchikov <me@xxxxxxxxxxxxx> wrote: > > 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/ Applied. Thanks
