bpf: make sure scalar args don't accept __arg_nonnull tag

Move scalar arg processing in btf_prepare_func_args() after all pointer
arg processing is done. This makes it easier to do validation. One
example of unintended behavior right now is ability to specify
__arg_nonnull for integer/enum arguments. This patch fixes this.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240105000909.2818934-3-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/btf.c

@@ -7058,10 +7058,6 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 
 		while (btf_type_is_modifier(t))
 			t = btf_type_by_id(btf, t->type);
-		if (btf_type_is_int(t) || btf_is_any_enum(t)) {
-			sub->args[i].arg_type = ARG_ANYTHING;
-			continue;
-		}
 		if (btf_type_is_ptr(t) && btf_get_prog_ctx_type(log, btf, t, prog_type, i)) {
 			sub->args[i].arg_type = ARG_PTR_TO_CTX;
 			continue;
@@ -7091,6 +7087,10 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 			bpf_log(log, "arg#%d marked as non-null, but is not a pointer type\n", i);
 			return -EINVAL;
 		}
+		if (btf_type_is_int(t) || btf_is_any_enum(t)) {
+			sub->args[i].arg_type = ARG_ANYTHING;
+			continue;
+		}
 		bpf_log(log, "Arg#%d type %s in %s() is not supported yet.\n",
 			i, btf_type_str(t), tname);
 		return -EINVAL;