add test

Author: tecki

tools/testing/selftests/bpf/progs/verifier_sock.c

@@ -1124,6 +1124,13 @@ int static_tail_call(struct __sk_buff *sk)
 	return 0;
 }
 
+static __noinline
+int *static_tail_call_return(struct __sk_buff *sk)
+{
+	bpf_tail_call_static(sk, &jmp_table, 0);
+	return (void *)(long)sk->data;
+}
+
 /* Tail calls in sub-programs invalidate packet pointers. */
 SEC("tc")
 __failure __msg("invalid mem access")
@@ -1166,4 +1173,18 @@ int invalidate_pkt_pointers_by_tail_call(struct __sk_buff *sk)
 	return TCX_PASS;
 }
 
+/* Direct tail calls do not invalidate packet pointers. */
+SEC("tc")
+__success
+int invalidate_pkt_pointers_by_tail_call_return(struct __sk_buff *sk)
+{
+	int *p = (void *)(long)sk->data;
+
+	if ((void *)(p + 1) > (void *)(long)sk->data_end)
+		return TCX_DROP;
+	p = bpf_tail_call_return(sk, &jmp_table, 0);
+	*p = 42; /* this is NOT unsafe: tail calls don't return */
+	return TCX_PASS;
+}
+
 char _license[] SEC("license") = "GPL";