On 18/7/26 06:49, Emil Tsalapatis wrote: > 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.
We are unable to implement it with a syscall example, because libbpf does not support creating a rdonly internal map for global percpu data. We have no '.ropercpu' section support in libbpf. Will add comment to explain the reason of hardcoded insns. Thanks, Leon > [...]
