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

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Date:   Wed, 1 Jul 2020 08:21:13 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     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 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.
So we won't be able to convert it to BTF in pahole.
Looking at how we failed to extend address_space() attribute to
support existing __rcu
and __user annotations I don't have high hopes of achieving annotations
via compiler (either gcc or clang). So plan B is to engage with sparse folks and
make it emit BTF with __rcu, __user and other annotations.