selftests/bpf: Add tests for user- and non-CO-RE BPF_CORE_READ() variants

Add selftests validating that newly added variations of BPF_CORE_READ(), for
use with user-space addresses and for non-CO-RE reads, work as expected.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20201218235614.2284956-4-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+
+#include <test_progs.h>
+
+struct callback_head {
+	struct callback_head *next;
+	void (*func)(struct callback_head *head);
+};
+
+/* ___shuffled flavor is just an illusion for BPF code, it doesn't really
+ * exist and user-space needs to provide data in the memory layout that
+ * matches callback_head. We just defined ___shuffled flavor to make it easier
+ * to work with the skeleton
+ */
+struct callback_head___shuffled {
+	struct callback_head___shuffled *next;
+	void (*func)(struct callback_head *head);
+};
+
+#include "test_core_read_macros.skel.h"
+
+void test_core_read_macros(void)
+{
+	int duration = 0, err;
+	struct test_core_read_macros* skel;
+	struct test_core_read_macros__bss *bss;
+	struct callback_head u_probe_in;
+	struct callback_head___shuffled u_core_in;
+
+	skel = test_core_read_macros__open_and_load();
+	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
+		return;
+	bss = skel->bss;
+	bss->my_pid = getpid();
+
+	/* next pointers have to be set from the kernel side */
+	bss->k_probe_in.func = (void *)(long)0x1234;
+	bss->k_core_in.func = (void *)(long)0xabcd;
+
+	u_probe_in.next = &u_probe_in;
+	u_probe_in.func = (void *)(long)0x5678;
+	bss->u_probe_in = &u_probe_in;
+
+	u_core_in.next = &u_core_in;
+	u_core_in.func = (void *)(long)0xdbca;
+	bss->u_core_in = &u_core_in;
+
+	err = test_core_read_macros__attach(skel);
+	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
+		goto cleanup;
+
+	/* trigger tracepoint */
+	usleep(1);
+
+	ASSERT_EQ(bss->k_probe_out, 0x1234, "k_probe_out");
+	ASSERT_EQ(bss->k_core_out, 0xabcd, "k_core_out");
+
+	ASSERT_EQ(bss->u_probe_out, 0x5678, "u_probe_out");
+	ASSERT_EQ(bss->u_core_out, 0xdbca, "u_core_out");
+
+cleanup:
+	test_core_read_macros__destroy(skel);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Facebook
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+
+char _license[] SEC("license") = "GPL";
+
+/* shuffled layout for relocatable (CO-RE) reads */
+struct callback_head___shuffled {
+	void (*func)(struct callback_head___shuffled *head);
+	struct callback_head___shuffled *next;
+};
+
+struct callback_head k_probe_in = {};
+struct callback_head___shuffled k_core_in = {};
+
+struct callback_head *u_probe_in = 0;
+struct callback_head___shuffled *u_core_in = 0;
+
+long k_probe_out = 0;
+long u_probe_out = 0;
+
+long k_core_out = 0;
+long u_core_out = 0;
+
+int my_pid = 0;
+
+SEC("raw_tracepoint/sys_enter")
+int handler(void *ctx)
+{
+	int pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (my_pid != pid)
+		return 0;
+
+	/* next pointers for kernel address space have to be initialized from
+	 * BPF side, user-space mmaped addresses are stil user-space addresses
+	 */
+	k_probe_in.next = &k_probe_in;
+	__builtin_preserve_access_index(({k_core_in.next = &k_core_in;}));
+
+	k_probe_out = (long)BPF_PROBE_READ(&k_probe_in, next, next, func);
+	k_core_out = (long)BPF_CORE_READ(&k_core_in, next, next, func);
+	u_probe_out = (long)BPF_PROBE_READ_USER(u_probe_in, next, next, func);
+	u_core_out = (long)BPF_CORE_READ_USER(u_core_in, next, next, func);
+
+	return 0;
+}