From: Christian Brauner <christian.brauner@ubuntu.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: YiFei Zhu <zhuyifei1999@gmail.com>,
containers@lists.linux.dev, bpf <bpf@vger.kernel.org>,
YiFei Zhu <yifeifz2@illinois.edu>,
LSM List <linux-security-module@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Austin Kuo <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>, Jinghao Jia <jinghao7@illinois.edu>,
Josep Torrellas <torrella@illinois.edu>,
Kees Cook <keescook@chromium.org>,
Sargun Dhillon <sargun@sargun.me>, Tianyin Xu <tyxu@illinois.edu>,
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 11:05:43 +0200 [thread overview]
Message-ID: <20210520090543.vay4guole7hkeaf3@wittgenstein> (raw)
In-Reply-To: <b3a1684b-86e4-74c4-184b-7700613aa838@kernel.org>
On Sat, May 15, 2021 at 08:49:01AM -0700, Andy Lutomirski 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://lists.linux-foundation.org/pipermail/containers/2018-February/038571.html
> >>>
> >>> 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.
Are you referring to sm like I sketched in
https://lore.kernel.org/containers/20210301110907.2qoxmiy55gpkgwnq@wittgenstein/
?
>
> >> eBPF doesn't really have a privilege model yet. There was a long and
> >> disappointing thread about this awhile back.
> >
> > The idea is that “seccomp-eBPF does not make life easier for an
> > adversary”. Any attack an adversary could potentially utilize
> > seccomp-eBPF, they can do the same with other eBPF features, i.e. it
> > would be an issue with eBPF in general rather than specifically
> > seccomp’s use of eBPF.
> >
> > Here it is referring to the helpers goes to the base
> > bpf_base_func_proto if the caller is unprivileged (!bpf_capable ||
> > !perfmon_capable). In this case, if the adversary would utilize eBPF
> > helpers to perform an attack, they could do it via another
> > unprivileged prog type.
> >
> > That said, there are a few additional helpers this patchset is adding:
> > * get_current_uid_gid
> > * get_current_pid_tgid
> > These two provide public information (are namespaces a concern?). I
If they are seen from userspace in any way then these must be resolved
relative to the caller's userns or caller's pidns. So yes, namespaces
need to be taken into account.
> > have no idea what kind of exploit it could add unless the adversary
> > somehow side-channels the task_struct? But in that case, how is the
> > reading of task_struct different from how the rest of the kernel is
> > reading task_struct?
>
> Yes, namespaces are a concern. This idea got mostly shot down for kdbus
> (what ever happened to that?), and it likely has the same problems for
> seccomp.
>
> >>
> >> What is this for?
> >
> > Memory reading opens up lots of use cases. For example, logging what
> > files are being opened without imposing too much performance penalty
> > from strace. Or as an accelerator for user notify emulation, where
> > syscalls can be rejected on a fast path if we know the memory contents
> > does not satisfy certain conditions that user notify will check.
> >
>
> This has all kinds of race conditions.
>
>
> I hate to be a party pooper, but this patchset is going to very high bar
> to acceptance. Right now, seccomp has a couple of excellent properties:
>
> First, while it has limited expressiveness, it is simple enough that the
> implementation can be easily understood and the scope for
> vulnerabilities that fall through the cracks of the seccomp sandbox
> model is low. Compare this to Windows' low-integrity/high-integrity
> sandbox system: there is a never ending string of sandbox escapes due to
> token misuse, unexpected things at various integrity levels, etc.
> Seccomp doesn't have tokens or integrity levels, and these bugs don't
> happen.
>
> Second, seccomp works, almost unchanged, in a completely unprivileged
> context. The last time making eBPF work sensibly in a less- or
Yeah, which is pretty important.
next prev parent reply other threads:[~2021-05-20 9:05 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 [this message]
[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
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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