selftests/bpf: Verify calling core kfuncs from BPF_PROG_TYPE_SYCALL

Now that we can call some kfuncs from BPF_PROG_TYPE_SYSCALL progs, let's
add some selftests that verify as much. As a bonus, let's also verify
that we can't call the progs from raw tracepoints. Do do this, we add a
new selftest suite called verifier_kfunc_prog_types.

Signed-off-by: David Vernet <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/prog_tests/verifier_kfunc_prog_types.c

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+
+#include "verifier_kfunc_prog_types.skel.h"
+
+void test_verifier_kfunc_prog_types(void)
+{
+	RUN_TESTS(verifier_kfunc_prog_types);
+}

tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h

···
 	struct cgroup __kptr * cgrp;
 };
 
-struct hash_map {
+struct {
 	__uint(type, BPF_MAP_TYPE_HASH);
 	__type(key, int);
 	__type(value, struct __cgrps_kfunc_map_value);

tools/testing/selftests/bpf/progs/task_kfunc_common.h

···
 	struct task_struct __kptr * task;
 };
 
-struct hash_map {
+struct {
 	__uint(type, BPF_MAP_TYPE_HASH);
 	__type(key, int);
 	__type(value, struct __tasks_kfunc_map_value);

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+#include "bpf_misc.h"
+#include "cgrp_kfunc_common.h"
+#include "cpumask_common.h"
+#include "task_kfunc_common.h"
+
+char _license[] SEC("license") = "GPL";
+
+/***************
+ * Task kfuncs *
+ ***************/
+
+static void task_kfunc_load_test(void)
+{
+	struct task_struct *current, *ref_1, *ref_2;
+
+	current = bpf_get_current_task_btf();
+	ref_1 = bpf_task_from_pid(current->pid);
+	if (!ref_1)
+		return;
+
+	ref_2 = bpf_task_acquire(ref_1);
+	if (ref_2)
+		bpf_task_release(ref_2);
+	bpf_task_release(ref_1);
+}
+
+SEC("raw_tp")
+__failure __msg("calling kernel function")
+int BPF_PROG(task_kfunc_raw_tp)
+{
+	task_kfunc_load_test();
+	return 0;
+}
+
+SEC("syscall")
+__success
+int BPF_PROG(task_kfunc_syscall)
+{
+	task_kfunc_load_test();
+	return 0;
+}
+
+/*****************
+ * cgroup kfuncs *
+ *****************/
+
+static void cgrp_kfunc_load_test(void)
+{
+	struct cgroup *cgrp, *ref;
+
+	cgrp = bpf_cgroup_from_id(0);
+	if (!cgrp)
+		return;
+
+	ref = bpf_cgroup_acquire(cgrp);
+	if (!ref) {
+		bpf_cgroup_release(cgrp);
+		return;
+	}
+
+	bpf_cgroup_release(ref);
+	bpf_cgroup_release(cgrp);
+}
+
+SEC("raw_tp")
+__failure __msg("calling kernel function")
+int BPF_PROG(cgrp_kfunc_raw_tp)
+{
+	cgrp_kfunc_load_test();
+	return 0;
+}
+
+SEC("syscall")
+__success
+int BPF_PROG(cgrp_kfunc_syscall)
+{
+	cgrp_kfunc_load_test();
+	return 0;
+}
+
+/******************
+ * cpumask kfuncs *
+ ******************/
+
+static void cpumask_kfunc_load_test(void)
+{
+	struct bpf_cpumask *alloc, *ref;
+
+	alloc = bpf_cpumask_create();
+	if (!alloc)
+		return;
+
+	ref = bpf_cpumask_acquire(alloc);
+	bpf_cpumask_set_cpu(0, alloc);
+	bpf_cpumask_test_cpu(0, (const struct cpumask *)ref);
+
+	bpf_cpumask_release(ref);
+	bpf_cpumask_release(alloc);
+}
+
+SEC("raw_tp")
+__failure __msg("calling kernel function")
+int BPF_PROG(cpumask_kfunc_raw_tp)
+{
+	cpumask_kfunc_load_test();
+	return 0;
+}
+
+SEC("syscall")
+__success
+int BPF_PROG(cpumask_kfunc_syscall)
+{
+	cpumask_kfunc_load_test();
+	return 0;
+}