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

[Chuyi Zhou]

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;
> > +    }
> > +}