On Tue, Jul 1, 2025 at 11:17 PM Kumar Kartikeya Dwivedi
<memxor@xxxxxxxxx> wrote:
>
> Begin reporting may_goto timeouts to BPF program's stderr stream.
>
> Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> kernel/bpf/core.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
Reviewed-by: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index ab8b3446570c..47dcc4f19050 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -3168,6 +3168,22 @@ u64 __weak arch_bpf_timed_may_goto(void)
> return 0;
> }
>
> +static noinline void bpf_prog_report_may_goto_violation(void)
> +{
> +#ifdef CONFIG_BPF_SYSCALL
> + struct bpf_stream_stage ss;
> + struct bpf_prog *prog;
> +
> + prog = bpf_prog_find_from_stack();
> + if (!prog)
> + return;
> + bpf_stream_stage(ss, prog, BPF_STDERR, ({
> + bpf_stream_printk(ss, "ERROR: Timeout detected for may_goto instruction\n");
> + bpf_stream_dump_stack(ss);
> + }));
> +#endif
> +}
> +
> u64 bpf_check_timed_may_goto(struct bpf_timed_may_goto *p)
> {
> u64 time = ktime_get_mono_fast_ns();
> @@ -3178,8 +3194,10 @@ u64 bpf_check_timed_may_goto(struct bpf_timed_may_goto *p)
> return BPF_MAX_TIMED_LOOPS;
> }
> /* Check if we've exhausted our time slice, and zero count. */
> - if (time - p->timestamp >= (NSEC_PER_SEC / 4))
> + if (unlikely(time - p->timestamp >= (NSEC_PER_SEC / 4))) {
> + bpf_prog_report_may_goto_violation();
> return 0;
> + }
> /* Refresh the count for the stack frame. */
> return BPF_MAX_TIMED_LOOPS;
> }
> --
> 2.47.1
>
