netdev - Re: [PATCH v5 bpf-next 2/5] bpf: Introduce sleepable BPF programs

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Message-ID: <CAADnVQJQFD2NTZRyqv1DHCFMcNRWn10Qnwnff-tL8iUYSbM91g@mail.gmail.com>
Date:   Fri, 10 Jul 2020 15:59:53 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        KP Singh <kpsingh@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v5 bpf-next 2/5] bpf: Introduce sleepable BPF programs

On Fri, Jul 10, 2020 at 10:00 AM Arnaldo Carvalho de Melo
<arnaldo.melo@...il.com> wrote:
>
> Em Wed, Jul 01, 2020 at 08:21:13AM -0700, Alexei Starovoitov escreveu:
> > On Wed, Jul 1, 2020 at 2:34 AM Daniel Borkmann <daniel@...earbox.net> wrote:
> > >
> > > +1, I think augmenting mid-term would be the best given check_sleepable_blacklist()
> > > is rather a very fragile workaround^hack and it's also a generic lsm/sec hooks issue
> >
> > I tried to make that crystal clear back in march during bpf virtual conference.
> > imo whitelist is just as fragile as blacklist. Underlying
> > implementation can change.
> >
> > > (at least for BPF_PROG_TYPE_LSM type & for the sake of documenting it for other LSMs).
> > > Perhaps there are function attributes that could be used and later retrieved via BTF?
> >
> > Even if we convince gcc folks to add another function attribute it
> > won't appear in dwarf.
>
> Warning, hack ahead!
>
> Perhaps we could do that with some sort of convention, i.e. define some
> type and make a function returning that type to have the desired
> attribute?
>
> I.e.
>
> typedef __attribute__foo__int int;
>
> __attribute__foo__int function_bla(...)
> {
> }
>
> ?

What about lsm hooks returning void ?
I guess for lsm we can hack something like that,
but for __rcu and __user that won't really work.
The kernel changes will be too massive.