selftests/bpf: Add tests for iter arg check

Add selftests to cover argument type check for iterator kfuncs, and
cover all three kinds (new, next, destroy). Without the fix in the
previous patch, the selftest would not cause a verifier error.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20241203000238.3602922-3-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: kkdwivedi

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

@@ -1486,4 +1486,30 @@ int iter_subprog_check_stacksafe(const void *ctx)
 	return 0;
 }
 
+struct bpf_iter_num global_it;
+
+SEC("raw_tp")
+__failure __msg("arg#0 expected pointer to an iterator on stack")
+int iter_new_bad_arg(const void *ctx)
+{
+	bpf_iter_num_new(&global_it, 0, 1);
+	return 0;
+}
+
+SEC("raw_tp")
+__failure __msg("arg#0 expected pointer to an iterator on stack")
+int iter_next_bad_arg(const void *ctx)
+{
+	bpf_iter_num_next(&global_it);
+	return 0;
+}
+
+SEC("raw_tp")
+__failure __msg("arg#0 expected pointer to an iterator on stack")
+int iter_destroy_bad_arg(const void *ctx)
+{
+	bpf_iter_num_destroy(&global_it);
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";