Re: [PATCH bpf-next] bpf: Avoid deadlock caused by nested kprobe and fentry bpf programs

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On Fri, Dec 13, 2024 at 5:59 PM 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.
>
> 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>

I've decided to apply to bpf tree.
We may need to whack-a-mole a bit more files until the resilient
spin lock is ready, but this is a good stop gap.

Thanks!





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