Subject: Re: [PATCH 1/6] ebpf: add a seccomp program type

From: Tycho Andersen <[email-masked]>
Date: Fri, 4 Sep 2015 15:06:15 -0600

On Fri, Sep 04, 2015 at 01:34:12PM -0700, Kees Cook wrote:
> On Fri, Sep 4, 2015 at 9:04 AM, Tycho Andersen
> <[email-masked]> wrote:
> > +static const struct bpf_func_proto *
> > +seccomp_func_proto(enum bpf_func_id func_id)
> > +{
> > +       /* Right now seccomp eBPF loading doesn't support maps; seccomp filters
> > +        * are considered to be read-only after they're installed, so map fds
> > +        * probably need to be invalidated when a seccomp filter with maps is
> > +        * installed.
> > +        *
> > +        * The rest of these might be reasonable to call from seccomp, so we
> > +        * export them.
> > +        */
> > +       switch (func_id) {
> > +       case BPF_FUNC_ktime_get_ns:
> > +               return &bpf_ktime_get_ns_proto;
> > +       case BPF_FUNC_trace_printk:
> > +               return bpf_get_trace_printk_proto();
> > +       case BPF_FUNC_get_prandom_u32:
> > +               return &bpf_get_prandom_u32_proto;
> > +       case BPF_FUNC_get_smp_processor_id:
> > +               return &bpf_get_smp_processor_id_proto;
> > +       case BPF_FUNC_tail_call:
> > +               return &bpf_tail_call_proto;
> > +       case BPF_FUNC_get_current_pid_tgid:
> > +               return &bpf_get_current_pid_tgid_proto;
> > +       case BPF_FUNC_get_current_uid_gid:
> > +               return &bpf_get_current_uid_gid_proto;
> > +       case BPF_FUNC_get_current_comm:
> > +               return &bpf_get_current_comm_proto;
> > +       default:
> > +               return NULL;
> > +       }
> > +}
> 
> While this list is probably fine, I don't want to mix the addition of
> eBPF functions to the seccomp ABI with the CRIU changes. No function
> calls are currently possible and it should stay that way.

Ok, I can remove them.

> I was expecting to see a validator, similar to the existing BPF
> validator that is called when creating seccomp filters currently. Can
> we add a similar validator for new BPF_PROG_TYPE_SECCOMP?

That's effectively what this patch does; when the eBPF is loaded via
bpf(), you tell bpf() you want a BPF_PROG_TYPE_SECCOMP, and it invokes
this validation/translation code, i.e. it uses
seccomp_is_valid_access() to check and make sure access are aligned
and inside struct seccomp_data.

Tycho