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From: KP Singh <kpsingh@chromium.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
	"David S. Miller" <davem@davemloft.net>,
	paulmck@kernel.org, Networking <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v5 bpf-next 2/5] bpf: Introduce sleepable BPF programs
Date: Wed, 1 Jul 2020 11:15:55 +0200
Message-ID: <CACYkzJ5kGxxA1E70EKah_hWbsb7hoUy8s_Y__uCeSyYxVezaBA@mail.gmail.com> (raw)
In-Reply-To: <20200630234117.arqmjpbivy5fhhmk@ast-mbp.dhcp.thefacebook.com>

On Wed, Jul 1, 2020 at 1:41 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Jul 01, 2020 at 01:26:44AM +0200, Daniel Borkmann wrote:
> > On 6/30/20 6:33 AM, Alexei Starovoitov wrote:
> > [...]
> > > +/* list of non-sleepable kernel functions that are otherwise
> > > + * available to attach by bpf_lsm or fmod_ret progs.
> > > + */
> > > +static int check_sleepable_blacklist(unsigned long addr)
> > > +{
> > > +#ifdef CONFIG_BPF_LSM
> > > +   if (addr == (long)bpf_lsm_task_free)
> > > +           return -EINVAL;
> > > +#endif
> > > +#ifdef CONFIG_SECURITY
> > > +   if (addr == (long)security_task_free)
> > > +           return -EINVAL;
> > > +#endif
> > > +   return 0;
> > > +}
> >
> > Would be nice to have some sort of generic function annotation to describe
> > that code cannot sleep inside of it, and then filter based on that. Anyway,
> > is above from manual code inspection?
>
> yep. all manual. I don't think there is a way to automate it.
> At least I cannot think of one.
>
> > What about others like security_sock_rcv_skb() for example which could be
> > bh_lock_sock()'ed (or, generally hooks running in softirq context)?
>
> ahh. it's in running in bh at that point? then it should be added to blacklist.
>
> The rough idea I had is to try all lsm_* and security_* hooks with all
> debug kernel flags and see which ones will complain. Then add them to blacklist.
> Unfortunately I'm completely swamped and cannot promise to do that
> in the coming months.
> So either we wait for somebody to do due diligence or land it knowing
> that blacklist is incomplete and fix it up one by one.
> I think the folks who're waiting on sleepable work would prefer the latter.
> I'm fine whichever way.

Chiming in since I belong to the folks who are waiting on sleepable BPF patches:

1. Let's obviously add security_sock_rcv_skb to the list.
2. I can help in combing through the LSM hooks (at least the comments)
     to look for any other obvious candidates.
3. I think it's okay (for us) for this list to be a WIP and build on it with
    proper warnings (in the changelog / comments).
4. To make it easier for figuring out which hooks cannot sleep,
     It would be nice if we could:

    * Have a helper say, bool bpf_cant_sleep(), available when
       DEBUG_ATOMIC_SLEEP is enabled.
    * Attach LSM programs to all hooks which call this helper and gather data.
    * Let this run on dev machines, run workloads which use the LSM hooks .

4. Finally, once we do the hard work. We can also think of augmenting the
    LSM_HOOK macro to have structured access to whether a hook is sleepable
    or not (instead of relying on comments).

- KP

  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-30  4:33 [PATCH v5 bpf-next 0/5] bpf: Introduce minimal support for sleepable progs Alexei Starovoitov
2020-06-30  4:33 ` [PATCH v5 bpf-next 1/5] bpf: Remove redundant synchronize_rcu Alexei Starovoitov
2020-06-30 20:55   ` Paul E. McKenney
2020-06-30  4:33 ` [PATCH v5 bpf-next 2/5] bpf: Introduce sleepable BPF programs Alexei Starovoitov
2020-06-30 22:04   ` Paul E. McKenney
2020-06-30 23:26   ` Daniel Borkmann
2020-06-30 23:41     ` Alexei Starovoitov
2020-07-01  9:15       ` KP Singh [this message]
2020-07-01  9:34         ` Daniel Borkmann
2020-07-01 15:21           ` Alexei Starovoitov
2020-07-01  9:17       ` Daniel Borkmann
2020-07-01 15:14         ` Alexei Starovoitov
2020-07-01 19:03           ` KP Singh
2020-06-30  4:33 ` [PATCH v5 bpf-next 3/5] bpf: Add bpf_copy_from_user() helper Alexei Starovoitov
2020-06-30 11:41   ` KP Singh
2020-06-30  4:33 ` [PATCH v5 bpf-next 4/5] libbpf: support sleepable progs Alexei Starovoitov
2020-06-30  4:33 ` [PATCH v5 bpf-next 5/5] selftests/bpf: Add sleepable tests Alexei Starovoitov
2020-06-30  5:14 ` [PATCH v5 bpf-next 0/5] bpf: Introduce minimal support for sleepable progs Andrii Nakryiko

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