Re: [PATCH bpf-next v2 2/6] bpf: Introduce css_task open-coded iterator kfuncs

Chuyi Zhou
2023-09-13T04:57:03Z

Hello Martin.

在 2023/9/13 03:57, Martin KaFai Lau 写道:
> On 9/12/23 12:01 AM, Chuyi Zhou wrote:
>> +__bpf_kfunc int bpf_iter_css_task_new(struct bpf_iter_css_task *it,
>> +        struct cgroup_subsys_state *css, unsigned int flags)
>> +{
>> +    struct bpf_iter_css_task_kern *kit = (void *)it;
>> +
>> +    BUILD_BUG_ON(sizeof(struct bpf_iter_css_task_kern) !=
>> sizeof(struct bpf_iter_css_task));
>> +    BUILD_BUG_ON(__alignof__(struct bpf_iter_css_task_kern) !=
>> +                    __alignof__(struct bpf_iter_css_task));
>> +
>> +    switch (flags) {
>> +    case CSS_TASK_ITER_PROCS | CSS_TASK_ITER_THREADED:
>> +    case CSS_TASK_ITER_PROCS:
>> +    case 0:
>> +        break;
>> +    default:
>> +        return -EINVAL;
>> +    }
>> +
>> +    kit->css_it = kzalloc(sizeof(struct css_task_iter), GFP_KERNEL);
>> +    if (!kit->css_it)
>> +        return -ENOMEM;
>> +    css_task_iter_start(css, flags, kit->css_it);
>> +    return 0;
>> +}
>> +
>
>> +static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
>> +{
>> +    enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
>> +
>> +    switch (prog_type) {
>> +    case BPF_PROG_TYPE_LSM:
>
> This will allow the non-sleepable lsm prog to call
> bpf_iter_css_task_new. The above kzalloc(GFP_KERNEL) in
> bpf_iter_css_task_new should trigger a lockdep error in the lsm selftest
> in patch 6.

Thanks for your test. I missed the dmesg error since I did not set
CONFIG_LOCKDEP.

I think here we can use kzalloc(GFP_ATOMIC) to eliminate this error if
we want to use this iter in non-sleepable lsm prog. I just tested, it
works well.

>
>> +        return true;
>> +    case BPF_TRACE_ITER:
>> +        return env->prog->aux->sleepable;
>> +    default:
>> +        return false;
>> +    }
>> +}
>