selftests/bpf: validate that tail call invalidates packet pointers

Add a test case with a tail call done from a global sub-program. Such
tails calls should be considered as invalidating packet pointers.

Signed-off-by: Eduard Zingerman <[email protected]>

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

@@ -50,6 +50,13 @@ struct {
 	__uint(map_flags, BPF_F_NO_PREALLOC);
 } sk_storage_map SEC(".maps");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u32));
+} jmp_table SEC(".maps");
+
 SEC("cgroup/skb")
 __description("skb->sk: no NULL check")
 __failure __msg("invalid mem access 'sock_common_or_null'")
@@ -1065,4 +1072,25 @@ int invalidate_pkt_pointers_from_global_func(struct __sk_buff *sk)
 	return TCX_PASS;
 }
 
+__noinline
+int tail_call(struct __sk_buff *sk)
+{
+	bpf_tail_call_static(sk, &jmp_table, 0);
+	return 0;
+}
+
+/* Tail calls invalidate packet pointers. */
+SEC("tc")
+__failure __msg("invalid mem access")
+int invalidate_pkt_pointers_by_tail_call(struct __sk_buff *sk)
+{
+	int *p = (void *)(long)sk->data;
+
+	if ((void *)(p + 1) > (void *)(long)sk->data_end)
+		return TCX_DROP;
+	tail_call(sk);
+	*p = 42; /* this is unsafe */
+	return TCX_PASS;
+}
+
 char _license[] SEC("license") = "GPL";