On Thu, 12 Dec 2024 at 18:58, Priya Bala Govindasamy <pgovind2@xxxxxxx> wrote: > > BPF program types like kprobe and fentry can cause deadlocks in certain > situations. If a function takes a lock and one of these bpf programs is > hooked to some point in the function's critical section, and if the > bpf program tries to call the same function and take the same lock it will > lead to deadlock. These situations have been reported in the following > bug reports. > > In percpu_freelist - > Link: https://lore.kernel.org/bpf/CAADnVQLAHwsa+2C6j9+UC6ScrDaN9Fjqv1WjB1pP9AzJLhKuLQ@xxxxxxxxxxxxxx/T/ > Link: https://lore.kernel.org/bpf/CAPPBnEYm+9zduStsZaDnq93q1jPLqO-PiKX9jy0MuL8LCXmCrQ@xxxxxxxxxxxxxx/T/ > In bpf_lru_list - > Link: https://lore.kernel.org/bpf/CAPPBnEajj+DMfiR_WRWU5=6A7KKULdB5Rob_NJopFLWF+i9gCA@xxxxxxxxxxxxxx/T/ > Link: https://lore.kernel.org/bpf/CAPPBnEZQDVN6VqnQXvVqGoB+ukOtHGZ9b9U0OLJJYvRoSsMY_g@xxxxxxxxxxxxxx/T/ > Link: https://lore.kernel.org/bpf/CAPPBnEaCB1rFAYU7Wf8UxqcqOWKmRPU1Nuzk3_oLk6qXR7LBOA@xxxxxxxxxxxxxx/T/ > > Similar bugs have been reported by syzbot. > In queue_stack_maps - > Link: https://lore.kernel.org/lkml/0000000000004c3fc90615f37756@xxxxxxxxxx/ > Link: https://lore.kernel.org/all/20240418230932.2689-1-hdanton@xxxxxxxx/T/ > In lpm_trie - > Link: https://lore.kernel.org/linux-kernel/00000000000035168a061a47fa38@xxxxxxxxxx/T/ > In ringbuf - > Link: https://lore.kernel.org/bpf/20240313121345.2292-1-hdanton@xxxxxxxx/T/ > > Prevent kprobe and fentry bpf programs from attaching to these critical > sections by removing CC_FLAGS_FTRACE for percpu_freelist.o, > bpf_lru_list.o, queue_stack_maps.o, lpm_trie.o, ringbuf.o files. > I think the current solution is to use a per-CPU variable to prevent deadlocks. You can look at the hashmap implementation for reference. However, ABBA deadlocks are still possible, so to avoid these, I think the BPF community is working towards implementing resilient spinlocks. I was planning to send patches for some of these bugs earlier. I'm wondering if per-CPU checks would still be valid once resilient spinlocks are introduced? > The bugs reported by syzbot are due to tracepoint bpf programs being > called in the critical sections. This patch does not aim to fix deadlocks > caused by tracepoint programs. However, it does prevent deadlocks from > occurring in similar situations due to kprobe and fentry programs. > > Signed-off-by: Priya Bala Govindasamy <pgovind2@xxxxxxx> > --- > kernel/bpf/Makefile | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile > index 7eb9ad3a3ae6..121ebcdc26cc 100644 > --- a/kernel/bpf/Makefile > +++ b/kernel/bpf/Makefile > @@ -52,3 +52,10 @@ obj-$(CONFIG_BPF_PRELOAD) += preload/ > obj-$(CONFIG_BPF_SYSCALL) += relo_core.o > $(obj)/relo_core.o: $(srctree)/tools/lib/bpf/relo_core.c FORCE > $(call if_changed_rule,cc_o_c) > + > +CFLAGS_REMOVE_percpu_freelist.o = $(CC_FLAGS_FTRACE) > +CFLAGS_REMOVE_bpf_lru_list.o = $(CC_FLAGS_FTRACE) > +CFLAGS_REMOVE_queue_stack_maps.o = $(CC_FLAGS_FTRACE) > +CFLAGS_REMOVE_lpm_trie.o = $(CC_FLAGS_FTRACE) > +CFLAGS_REMOVE_ringbuf.o = $(CC_FLAGS_FTRACE) > + > -- > 2.34.1 >
