[PATCH bpf-next v5 07/12] bpf: Report may_goto timeout to BPF stderr

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Begin reporting may_goto timeouts to BPF program's stderr stream.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/core.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 037d67cf5fb1..fe8a53f3c5bc 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