On Wed Jul 15, 2026 at 11:32 AM EDT, Leon Hwang wrote:
> 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 <[email protected]>
> ---
> .../bpf/prog_tests/global_data_init.c | 83 +++++++++++++++++++
> 1 file changed, 83 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 f7a56e3fdbce..d4405646847a 100644
> --- a/tools/testing/selftests/bpf/prog_tests/global_data_init.c
> +++ b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
> @@ -199,6 +199,85 @@ 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)
> +{
> + 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(),
> + };
Why hardcode this as inline assembly? Can we do a syscall example in the
progs/? That way there will also be a concrete example of how we're
using the feature in practice.
> + 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);
> + 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)) {
> @@ -210,4 +289,8 @@ 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();
> }
