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From: Tianyin Xu <tyxu@illinois.edu>
To: Tycho Andersen <tycho@tycho.pizza>
Cc: Andy Lutomirski <luto@kernel.org>,
	YiFei Zhu <zhuyifei1999@gmail.com>,
	"containers@lists.linux.dev" <containers@lists.linux.dev>,
	bpf <bpf@vger.kernel.org>, "Zhu, YiFei" <yifeifz2@illinois.edu>,
	LSM List <linux-security-module@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	"Kuo, Hsuan-Chi" <hckuo2@illinois.edu>,
	Claudio Canella <claudio.canella@iaik.tugraz.at>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
	Dimitrios Skarlatos <dskarlat@cs.cmu.edu>,
	Giuseppe Scrivano <gscrivan@redhat.com>,
	Hubertus Franke <frankeh@us.ibm.com>,
	Jann Horn <jannh@google.com>,
	"Jia, Jinghao" <jinghao7@illinois.edu>,
	"Torrellas, Josep" <torrella@illinois.edu>,
	Kees Cook <keescook@chromium.org>,
	Sargun Dhillon <sargun@sargun.me>,
	Tobin Feldman-Fitzthum <tobin@ibm.com>,
	Tom Hromatka <tom.hromatka@oracle.com>,
	Will Drewry <wad@chromium.org>
Subject: Re: [RFC PATCH bpf-next seccomp 00/12] eBPF seccomp filters
Date: Thu, 20 May 2021 03:16:10 -0500	[thread overview]
Message-ID: <CAGMVDEEkDeUBcJAswpBjcQNWk7QDcO8BZR=uvVfm-+qe714tYg@mail.gmail.com> (raw)
In-Reply-To: <108b4b9c2daa4123805d2b92cf51374b@DM5PR11MB1692.namprd11.prod.outlook.com>

On Mon, May 17, 2021 at 10:40 AM Tycho Andersen <tycho@tycho.pizza> wrote:
>
> On Sun, May 16, 2021 at 03:38:00AM -0500, Tianyin Xu wrote:
> > On Sat, May 15, 2021 at 10:49 AM Andy Lutomirski <luto@kernel.org> wrote:
> > >
> > > On 5/10/21 10:21 PM, YiFei Zhu wrote:
> > > > On Mon, May 10, 2021 at 12:47 PM Andy Lutomirski <luto@kernel.org> wrote:
> > > >> On Mon, May 10, 2021 at 10:22 AM YiFei Zhu <zhuyifei1999@gmail.com> wrote:
> > > >>>
> > > >>> From: YiFei Zhu <yifeifz2@illinois.edu>
> > > >>>
> > > >>> Based on: https://urldefense.com/v3/__https://lists.linux-foundation.org/pipermail/containers/2018-February/038571.html__;!!DZ3fjg!thbAoRgmCeWjlv0qPDndNZW1j6Y2Kl_huVyUffr4wVbISf-aUiULaWHwkKJrNJyo$
> > > >>>
> > > >>> This patchset enables seccomp filters to be written in eBPF.
> > > >>> Supporting eBPF filters has been proposed a few times in the past.
> > > >>> The main concerns were (1) use cases and (2) security. We have
> > > >>> identified many use cases that can benefit from advanced eBPF
> > > >>> filters, such as:
> > > >>
> > > >> I haven't reviewed this carefully, but I think we need to distinguish
> > > >> a few things:
> > > >>
> > > >> 1. Using the eBPF *language*.
> > > >>
> > > >> 2. Allowing the use of stateful / non-pure eBPF features.
> > > >>
> > > >> 3. Allowing the eBPF programs to read the target process' memory.
> > > >>
> > > >> I'm generally in favor of (1).  I'm not at all sure about (2), and I'm
> > > >> even less convinced by (3).
> > > >>
> > > >>>
> > > >>>   * exec-only-once filter / apply filter after exec
> > > >>
> > > >> This is (2).  I'm not sure it's a good idea.
> > > >
> > > > The basic idea is that for a container runtime it may wait to execute
> > > > a program in a container without that program being able to execve
> > > > another program, stopping any attack that involves loading another
> > > > binary. The container runtime can block any syscall but execve in the
> > > > exec-ed process by using only cBPF.
> > > >
> > > > The use case is suggested by Andrea Arcangeli and Giuseppe Scrivano.
> > > > @Andrea and @Giuseppe, could you clarify more in case I missed
> > > > something?
> > >
> > > We've discussed having a notifier-using filter be able to replace its
> > > filter.  This would allow this and other use cases without any
> > > additional eBPF or cBPF code.
> > >
> >
> > A notifier is not always a solution (even ignoring its perf overhead).
> >
> > One problem, pointed out by Andrea Arcangeli, is that notifiers need
> > userspace daemons. So, it can hardly be used by daemonless container
> > engines like Podman.
>
> I'm not sure I buy this argument. Podman already has a conmon instance
> for each container, this could be a child of that conmon process, or
> live inside conmon itself.
>
> Tycho

I checked with Andrea Arcangeli and Giuseppe Scrivano who are working on Podman.

You are right that Podman is not completely daemonless. However, “the
fact it's no entirely daemonless doesn't imply it's a good idea to
make it worse and to add complexity to the background conmon daemon or
to add more daemons.”

TL;DR. User notifiers are surely more flexible, but are also more
expensive and complex to implement, compared with ebpf filters. /*
I’ll reply to Sargun’s performance argument in a separate email */

I'm sure you know Podman well, but let me still move some jade from
Andrea and Giuseppe (all credits on podmon/crun are theirs) to
elaborate the point, for folks cced on the list who are not very
familiar with Podman.

Basically, the current order goes as follows:

         podman -> conmon -> crun -> container_binary
                               \
                                - seccomp done at crun level, not conmon

At runtime, what's left is:

         conmon -> container_binary  /* podman disappears; crun disappears */

So, to go through and use seccomp notify to block `exec`, we can
either start the container_binary with a seccomp agent wrapper, or
bloat the common binary (as pointed out by Tycho).

If we go with the first approach, we will have:

         podman -> conmon -> crun -> seccomp_agent -> container_binary

So, at runtime we'd be left with one more daemon:

        conmon -> seccomp_agent -> container_binary

Apparently, nobody likes one more daemon. So, the proposal from
Giuseppe was/is to use user notifiers as plugins (.so) loaded by
conmon:
https://github.com/containers/conmon/pull/190
https://github.com/containers/crun/pull/438

Now, with the ebpf filter support, one can implement the same thing
using an embarrassingly simple ebpf filter and, thanks to Giuseppe,
this is well supported by crun.

-- 
Tianyin Xu
University of Illinois at Urbana-Champaign
https://tianyin.github.io/

  parent reply	other threads:[~2021-05-20  8:39 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10 17:22 [RFC PATCH bpf-next seccomp 00/12] eBPF seccomp filters YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 01/12] seccomp: Move no_new_privs check to after prepare_filter YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 02/12] bpf, seccomp: Add eBPF filter capabilities YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 03/12] seccomp, ptrace: Add a mechanism to retrieve attached eBPF seccomp filters YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 04/12] libbpf: recognize section "seccomp" YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 05/12] samples/bpf: Add eBPF seccomp sample programs YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 06/12] lsm: New hook seccomp_extended YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 07/12] bpf/verifier: allow restricting direct map access YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 08/12] seccomp-ebpf: restrict filter to almost cBPF if LSM request such YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 09/12] yama: (concept) restrict seccomp-eBPF with ptrace_scope YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 10/12] seccomp-ebpf: Add ability to read user memory YiFei Zhu
2021-05-11  2:04   ` Alexei Starovoitov
2021-05-11  7:14     ` YiFei Zhu
2021-05-12 22:36       ` Alexei Starovoitov
2021-05-13  5:26         ` YiFei Zhu
2021-05-13 14:53           ` Andy Lutomirski
2021-05-13 17:12             ` YiFei Zhu
2021-05-13 17:15               ` Andy Lutomirski
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 11/12] bpf/verifier: support NULL-able ptr to BTF ID as helper argument YiFei Zhu
2021-05-10 17:22 ` [RFC PATCH bpf-next seccomp 12/12] seccomp-ebpf: support task storage from BPF-LSM, defaulting to group leader YiFei Zhu
2021-05-11  1:58   ` Alexei Starovoitov
2021-05-11  5:44     ` YiFei Zhu
2021-05-12 21:56       ` Alexei Starovoitov
2021-05-10 17:47 ` [RFC PATCH bpf-next seccomp 00/12] eBPF seccomp filters Andy Lutomirski
2021-05-11  5:21   ` YiFei Zhu
2021-05-15 15:49     ` Andy Lutomirski
2021-05-20  9:05       ` Christian Brauner
     [not found]     ` <fffbea8189794a8da539f6082af3de8e@DM5PR11MB1692.namprd11.prod.outlook.com>
2021-05-16  8:38       ` Tianyin Xu
2021-05-17 15:40         ` Tycho Andersen
2021-05-17 17:07         ` Sargun Dhillon
     [not found]         ` <108b4b9c2daa4123805d2b92cf51374b@DM5PR11MB1692.namprd11.prod.outlook.com>
2021-05-20  8:16           ` Tianyin Xu [this message]
2021-05-20  8:56             ` Christian Brauner
2021-05-20  9:37               ` Christian Brauner
2021-06-01 19:55               ` Kees Cook
2021-06-09  6:32                 ` Jinghao Jia
2021-06-09  6:27               ` Jinghao Jia
     [not found]             ` <00fe481c572d486289bc88780f48e88f@DM5PR11MB1692.namprd11.prod.outlook.com>
2021-05-20 22:13               ` Tianyin Xu
     [not found]         ` <eae2a0e5038b41c4af87edcb3d4cdc13@DM5PR11MB1692.namprd11.prod.outlook.com>
2021-05-20  8:22           ` Tianyin Xu
2021-05-24 18:55             ` Sargun Dhillon

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