[PATCH bpf-next v12 08/10] selftests/bpf: Test direct reading/writing read-only percpu_array map

[Leon Hwang <leon.hwang@linux.dev>]

Verify these two cases:

1. Direct reading the data of read-only percpu data's percpu_array map
   is allowed.
2. Direct writing the data of read-only percpu data's percpu_array map
   is disallowed.

Assisted-by: Codex:gpt-5.5-xhigh
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 .../bpf/prog_tests/global_data_init.c         | 90 +++++++++++++++++++
 1 file changed, 90 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/global_data_init.c b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
index 06d163a022dc..9688b417a90b 100644
--- a/tools/testing/selftests/bpf/prog_tests/global_data_init.c
+++ b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
@@ -236,6 +236,92 @@ static void test_global_percpu_data_lskel(void)
 	test_global_percpu_data_lskel__destroy(lskel);
 }
 
+static int create_rdonly_percpu_array(void)
+{
+	LIBBPF_OPTS(bpf_map_create_opts, map_opts,
+		    .map_flags = BPF_F_RDONLY_PROG,
+	);
+	int key = 0, map_fd, err;
+	__u64 value = 0;
+
+	map_fd = bpf_map_create(BPF_MAP_TYPE_PERCPU_ARRAY, "percpu_ro_map", sizeof(int),
+				sizeof(__u64), 1, &map_opts);
+	if (!ASSERT_GE(map_fd, 0, "bpf_map_create"))
+		return -1;
+
+	err = bpf_map_update_elem(map_fd, &key, &value, BPF_F_ALL_CPUS);
+	if (!ASSERT_OK(err, "bpf_map_update_elem"))
+		goto out;
+
+	err = bpf_map_freeze(map_fd);
+	if (!ASSERT_OK(err, "bpf_map_freeze"))
+		goto out;
+
+	return map_fd;
+
+out:
+	close(map_fd);
+	return -1;
+}
+
+static void test_global_percpu_data_rdonly_direct_read(void)
+{
+	/*
+	 * Raw instructions with manually prepared rdonly percpu_array map
+	 * for testing direct-read global percpu data, because libbpf
+	 * doesn't have rdonly internal percpu_array map support for
+	 * global percpu data.
+	 */
+	struct bpf_insn insns[] = {
+		BPF_LD_MAP_VALUE(BPF_REG_1, 0, 0),
+		BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 0),
+		BPF_EXIT_INSN(),
+	};
+	int map_fd, prog_fd;
+
+	map_fd = create_rdonly_percpu_array();
+	if (map_fd < 0)
+		return;
+
+	insns[0].imm = map_fd;
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "percpu_ro_prog", "GPL", insns,
+				ARRAY_SIZE(insns), NULL);
+	if (ASSERT_GE(prog_fd, 0, "bpf_prog_load"))
+		close(prog_fd);
+	close(map_fd);
+}
+
+static void test_global_percpu_data_rdonly_direct_write(void)
+{
+	LIBBPF_OPTS(bpf_prog_load_opts, prog_opts);
+	/* See the comment in test_global_percpu_data_rdonly_direct_read() */
+	struct bpf_insn insns[] = {
+		BPF_LD_MAP_VALUE(BPF_REG_1, 0, 0),
+		BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 0),
+		BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 0),
+		BPF_EXIT_INSN(),
+	};
+	char log_buf[256] = {};
+	int map_fd, prog_fd;
+
+	prog_opts.log_buf = log_buf;
+	prog_opts.log_size = sizeof(log_buf);
+	prog_opts.log_level = 1;
+
+	map_fd = create_rdonly_percpu_array();
+	if (map_fd < 0)
+		return;
+
+	insns[0].imm = map_fd;
+	prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, "percpu_ro_prog", "GPL", insns,
+				ARRAY_SIZE(insns), &prog_opts);
+	if (!ASSERT_LT(prog_fd, 0, "bpf_prog_load"))
+		close(prog_fd);
+	else
+		ASSERT_HAS_SUBSTR(log_buf, "write into map forbidden", "verifier log");
+	close(map_fd);
+}
+
 void test_global_percpu_data(void)
 {
 	if (!feat_supported(NULL, FEAT_PERCPU_DATA)) {
@@ -247,4 +333,8 @@ void test_global_percpu_data(void)
 		test_global_percpu_data_init();
 	if (test__start_subtest("lskel"))
 		test_global_percpu_data_lskel();
+	if (test__start_subtest("rdonly_direct_read"))
+		test_global_percpu_data_rdonly_direct_read();
+	if (test__start_subtest("rdonly_direct_write"))
+		test_global_percpu_data_rdonly_direct_write();
 }
-- 
2.55.0