bpf: Avoid deadlock caused by nested kprobe and fentry bpf programs

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@mail.gmail.com/T/
Link: https://lore.kernel.org/bpf/CAPPBnEYm+9zduStsZaDnq93q1jPLqO-PiKX9jy0MuL8LCXmCrQ@mail.gmail.com/T/
In bpf_lru_list -
Link: https://lore.kernel.org/bpf/CAPPBnEajj+DMfiR_WRWU5=6A7KKULdB5Rob_NJopFLWF+i9gCA@mail.gmail.com/T/
Link: https://lore.kernel.org/bpf/CAPPBnEZQDVN6VqnQXvVqGoB+ukOtHGZ9b9U0OLJJYvRoSsMY_g@mail.gmail.com/T/
Link: https://lore.kernel.org/bpf/CAPPBnEaCB1rFAYU7Wf8UxqcqOWKmRPU1Nuzk3_oLk6qXR7LBOA@mail.gmail.com/T/

Similar bugs have been reported by syzbot.
In queue_stack_maps -
Link: https://lore.kernel.org/lkml/[email protected]/
Link: https://lore.kernel.org/all/[email protected]/T/
In lpm_trie -
Link: https://lore.kernel.org/linux-kernel/[email protected]/T/
In ringbuf -
Link: https://lore.kernel.org/bpf/[email protected]/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.

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 <[email protected]>
Link: https://lore.kernel.org/r/CAPPBnEZpjGnsuA26Mf9kYibSaGLm=oF6=12L21X1GEQdqjLnzQ@mail.gmail.com
Signed-off-by: Alexei Starovoitov <[email protected]>

kernel/bpf/Makefile

@@ -53,3 +53,9 @@ obj-$(CONFIG_BPF_SYSCALL) += relo_core.o
 obj-$(CONFIG_BPF_SYSCALL) += btf_iter.o
 obj-$(CONFIG_BPF_SYSCALL) += btf_relocate.o
 obj-$(CONFIG_BPF_SYSCALL) += kmem_cache_iter.o
+
+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)