selftests/bpf: Add non-BPF_LSM test for task local storage

Task local storage is enabled for tracing programs. Add two tests for
task local storage without CONFIG_BPF_LSM.

The first test stores a value in sys_enter and read it back in sys_exit.

The second test checks whether the kernel allows allocating task local
storage in exit_creds() (which it should not).
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210225234319.336131-4-songliubraving@fb.com

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#define _GNU_SOURCE         /* See feature_test_macros(7) */
+#include <unistd.h>
+#include <sys/syscall.h>   /* For SYS_xxx definitions */
+#include <sys/types.h>
+#include <test_progs.h>
+#include "task_local_storage.skel.h"
+#include "task_local_storage_exit_creds.skel.h"
+
+static void test_sys_enter_exit(void)
+{
+	struct task_local_storage *skel;
+	int err;
+
+	skel = task_local_storage__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
+		return;
+
+	skel->bss->target_pid = syscall(SYS_gettid);
+
+	err = task_local_storage__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto out;
+
+	syscall(SYS_gettid);
+	syscall(SYS_gettid);
+
+	/* 3x syscalls: 1x attach and 2x gettid */
+	ASSERT_EQ(skel->bss->enter_cnt, 3, "enter_cnt");
+	ASSERT_EQ(skel->bss->exit_cnt, 3, "exit_cnt");
+	ASSERT_EQ(skel->bss->mismatch_cnt, 0, "mismatch_cnt");
+out:
+	task_local_storage__destroy(skel);
+}
+
+static void test_exit_creds(void)
+{
+	struct task_local_storage_exit_creds *skel;
+	int err;
+
+	skel = task_local_storage_exit_creds__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
+		return;
+
+	err = task_local_storage_exit_creds__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach"))
+		goto out;
+
+	/* trigger at least one exit_creds() */
+	if (CHECK_FAIL(system("ls > /dev/null")))
+		goto out;
+
+	/* sync rcu to make sure exit_creds() is called for "ls" */
+	kern_sync_rcu();
+	ASSERT_EQ(skel->bss->valid_ptr_count, 0, "valid_ptr_count");
+	ASSERT_NEQ(skel->bss->null_ptr_count, 0, "null_ptr_count");
+out:
+	task_local_storage_exit_creds__destroy(skel);
+}
+
+void test_task_local_storage(void)
+{
+	if (test__start_subtest("sys_enter_exit"))
+		test_sys_enter_exit();
+	if (test__start_subtest("exit_creds"))
+		test_exit_creds();
+}

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, long);
+} enter_id SEC(".maps");
+
+#define MAGIC_VALUE 0xabcd1234
+
+pid_t target_pid = 0;
+int mismatch_cnt = 0;
+int enter_cnt = 0;
+int exit_cnt = 0;
+
+SEC("tp_btf/sys_enter")
+int BPF_PROG(on_enter, struct pt_regs *regs, long id)
+{
+	struct task_struct *task;
+	long *ptr;
+
+	task = bpf_get_current_task_btf();
+	if (task->pid != target_pid)
+		return 0;
+
+	ptr = bpf_task_storage_get(&enter_id, task, 0,
+				   BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (!ptr)
+		return 0;
+
+	__sync_fetch_and_add(&enter_cnt, 1);
+	*ptr = MAGIC_VALUE + enter_cnt;
+
+	return 0;
+}
+
+SEC("tp_btf/sys_exit")
+int BPF_PROG(on_exit, struct pt_regs *regs, long id)
+{
+	struct task_struct *task;
+	long *ptr;
+
+	task = bpf_get_current_task_btf();
+	if (task->pid != target_pid)
+		return 0;
+
+	ptr = bpf_task_storage_get(&enter_id, task, 0,
+				   BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (!ptr)
+		return 0;
+
+	__sync_fetch_and_add(&exit_cnt, 1);
+	if (*ptr != MAGIC_VALUE + exit_cnt)
+		__sync_fetch_and_add(&mismatch_cnt, 1);
+	return 0;
+}

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, __u64);
+} task_storage SEC(".maps");
+
+int valid_ptr_count = 0;
+int null_ptr_count = 0;
+
+SEC("fentry/exit_creds")
+int BPF_PROG(trace_exit_creds, struct task_struct *task)
+{
+	__u64 *ptr;
+
+	ptr = bpf_task_storage_get(&task_storage, task, 0,
+				   BPF_LOCAL_STORAGE_GET_F_CREATE);
+	if (ptr)
+		__sync_fetch_and_add(&valid_ptr_count, 1);
+	else
+		__sync_fetch_and_add(&null_ptr_count, 1);
+	return 0;
+}