From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Stephen Smalley <sds@tycho.nsa.gov>
Cc: "KP Singh" <kpsingh@chromium.org>,
"James Morris" <jmorris@namei.org>,
"Kees Cook" <keescook@chromium.org>,
"Casey Schaufler" <casey@schaufler-ca.com>,
"open list" <linux-kernel@vger.kernel.org>,
bpf <bpf@vger.kernel.org>,
linux-security-module@vger.kernel.org,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Thomas Garnier" <thgarnie@chromium.org>,
"Michael Halcrow" <mhalcrow@google.com>,
"Paul Turner" <pjt@google.com>,
"Brendan Gregg" <brendan.d.gregg@gmail.com>,
"Jann Horn" <jannh@google.com>,
"Matthew Garrett" <mjg59@google.com>,
"Christian Brauner" <christian@brauner.io>,
"Mickaël Salaün" <mic@digikod.net>,
"Florent Revest" <revest@chromium.org>,
"Brendan Jackman" <jackmanb@chromium.org>,
"Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
"Mauro Carvalho Chehab" <mchehab+samsung@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Nicolas Ferre" <nicolas.ferre@microchip.com>,
"Stanislav Fomichev" <sdf@google.com>,
"Quentin Monnet" <quentin.monnet@netronome.com>,
"Andrey Ignatov" <rdna@fb.com>, "Joe Stringer" <joe@wand.net.nz>,
"Paul Moore" <paul@paul-moore.com>
Subject: Re: [PATCH bpf-next v1 00/13] MAC and Audit policy using eBPF (KRSI)
Date: Tue, 14 Jan 2020 18:48:32 -0800 [thread overview]
Message-ID: <20200115024830.4ogd3mi5jy5hwr2v@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <49a45583-b4fb-6353-a8d4-6f49287b26eb@tycho.nsa.gov>
On Tue, Jan 14, 2020 at 12:42:22PM -0500, Stephen Smalley wrote:
> On 1/14/20 11:54 AM, Stephen Smalley wrote:
> > On 1/10/20 12:53 PM, Alexei Starovoitov wrote:
> > > On Fri, Jan 10, 2020 at 04:27:58PM +0100, KP Singh wrote:
> > > > On 09-Jan 14:47, Stephen Smalley wrote:
> > > > > On 1/9/20 2:43 PM, KP Singh wrote:
> > > > > > On 10-Jan 06:07, James Morris wrote:
> > > > > > > On Thu, 9 Jan 2020, Stephen Smalley wrote:
> > > > > > >
> > > > > > > > On 1/9/20 1:11 PM, James Morris wrote:
> > > > > > > > > On Wed, 8 Jan 2020, Stephen Smalley wrote:
> > > > > > > > >
> > > > > > > > > > The cover letter subject line and the
> > > > > > > > > > Kconfig help text refer to it as a
> > > > > > > > > > BPF-based "MAC and Audit policy". It
> > > > > > > > > > has an enforce config option that
> > > > > > > > > > enables the bpf programs to deny access,
> > > > > > > > > > providing access control. IIRC,
> > > > > > > > > > in
> > > > > > > > > > the earlier discussion threads, the BPF
> > > > > > > > > > maintainers suggested that Smack
> > > > > > > > > > and
> > > > > > > > > > other LSMs could be entirely
> > > > > > > > > > re-implemented via it in the future, and
> > > > > > > > > > that
> > > > > > > > > > such an implementation would be more optimal.
> > > > > > > > >
> > > > > > > > > In this case, the eBPF code is similar to a
> > > > > > > > > kernel module, rather than a
> > > > > > > > > loadable policy file. It's a loadable
> > > > > > > > > mechanism, rather than a policy, in
> > > > > > > > > my view.
> > > > > > > >
> > > > > > > > I thought you frowned on dynamically loadable
> > > > > > > > LSMs for both security and
> > > > > > > > correctness reasons?
> > > > > >
> > > > > > Based on the feedback from the lists we've updated the design for v2.
> > > > > >
> > > > > > In v2, LSM hook callbacks are allocated dynamically using BPF
> > > > > > trampolines, appended to a separate security_hook_heads and run
> > > > > > only after the statically allocated hooks.
> > > > > >
> > > > > > The security_hook_heads for all the other LSMs (SELinux, AppArmor etc)
> > > > > > still remains __lsm_ro_after_init and cannot be modified. We are still
> > > > > > working on v2 (not ready for review yet) but the general idea can be
> > > > > > seen here:
> > > > > >
> > > > > > https://github.com/sinkap/linux-krsi/blob/patch/v1/trampoline_prototype/security/bpf/lsm.c
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > Evaluating the security impact of this is the next
> > > > > > > step. My understanding
> > > > > > > is that eBPF via BTF is constrained to read only access to hook
> > > > > > > parameters, and that its behavior would be entirely restrictive.
> > > > > > >
> > > > > > > I'd like to understand the security impact more
> > > > > > > fully, though. Can the
> > > > > > > eBPF code make arbitrary writes to the kernel, or
> > > > > > > read anything other than
> > > > > > > the correctly bounded LSM hook parameters?
> > > > > > >
> > > > > >
> > > > > > As mentioned, the BPF verifier does not allow writes to BTF types.
> > > > > >
> > > > > > > > And a traditional security module would necessarily fall
> > > > > > > > under GPL; is the eBPF code required to be
> > > > > > > > likewise? If not, KRSI is a
> > > > > > > > gateway for proprietary LSMs...
> > > > > > >
> > > > > > > Right, we do not want this to be a GPL bypass.
> > > > > >
> > > > > > This is not intended to be a GPL bypass and the BPF verifier checks
> > > > > > for license compatibility of the loaded program with GPL.
> > > > >
> > > > > IIUC, it checks that the program is GPL compatible if it
> > > > > uses a function
> > > > > marked GPL-only. But what specifically is marked GPL-only
> > > > > that is required
> > > > > for eBPF programs using KRSI?
> > > >
> > > > Good point! If no-one objects, I can add it to the BPF_PROG_TYPE_LSM
> > > > specific verification for the v2 of the patch-set which would require
> > > > all BPF-LSM programs to be GPL.
> > >
> > > I don't think it's a good idea to enforce license on the program.
> > > The kernel doesn't do it for modules.
> > > For years all of BPF tracing progs were GPL because they have to use
> > > GPL-ed helpers to do anything meaningful.
> > > So for KRSI just make sure that all helpers are GPL-ed as well.
> >
> > IIUC, the example eBPF code included in this patch series showed a
> > program that used a GPL-only helper for the purpose of reporting event
> > output to userspace. But it could have just as easily omitted the use of
> > that helper and still implemented its own arbitrary access control model
> > on the LSM hooks to which it attached. It seems like the question is
> > whether the kernel developers are ok with exposing the entire LSM hook
> > interface and all the associated data structures to non-GPLd code,
> > irrespective of what helpers it may or may not use.
>
> Also, to be clear, while kernel modules aren't necessarily GPL, prior to
> this patch series, all Linux security modules were necessarily GPLd in order
> to use the LSM interface.
Because they use securityfs_create_file() GPL-ed api, right?
but not because module license is enforced.
> So allowing non-GPL eBPF-based LSMs would be a
> change.
I don't see it this way. seccomp progs technically unlicensed. Yet they can
disallow any syscall. Primitive KRSI progs like
int bpf-prog(void*) { return REJECT; }
would be able to do selectively disable a syscall with an overhead acceptable
in production systems (unlike seccomp). I want this use case to be available to
people. It's a bait, because to do real progs people would need to GPL them.
Key helpers bpf_perf_event_output, bpf_ktime_get_ns, bpf_trace_printk are all
GPL-ed. It may look that most networking helpers are not-GPL, but real life is
different. To debug programs bpf_trace_printk() is necessary. To have
communication with user space bpf_perf_event_output() is necssary. To measure
anything or implement timestamps bpf_ktime_get_ns() is necessary. So today all
meaninful bpf programs are GPL. Those that are not GPL probably exist, but
they're toy programs. Hence I have zero concerns about GPL bypass coming from
tracing, networking, and, in the future, KRSI progs too.
next prev parent reply other threads:[~2020-01-15 2:48 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-20 15:41 [PATCH bpf-next v1 00/13] MAC and Audit policy using eBPF (KRSI) KP Singh
2019-12-20 15:41 ` [PATCH bpf-next v1 01/13] bpf: Refactor BPF_EVENT context macros to its own header KP Singh
2019-12-20 20:10 ` Andrii Nakryiko
2019-12-20 20:26 ` KP Singh
2019-12-20 15:41 ` [PATCH bpf-next v1 02/13] bpf: lsm: Add a skeleton and config options KP Singh
2020-01-07 21:13 ` James Morris
2019-12-20 15:41 ` [PATCH bpf-next v1 03/13] bpf: lsm: Introduce types for eBPF based LSM KP Singh
2019-12-20 15:41 ` [PATCH bpf-next v1 04/13] bpf: lsm: Allow btf_id based attachment for LSM hooks KP Singh
2019-12-23 23:54 ` Andrii Nakryiko
2019-12-30 19:22 ` KP Singh
2019-12-20 15:42 ` [PATCH bpf-next v1 05/13] tools/libbpf: Add support in libbpf for BPF_PROG_TYPE_LSM KP Singh
2019-12-24 0:07 ` Andrii Nakryiko
2019-12-24 0:09 ` Andrii Nakryiko
2020-01-03 23:59 ` KP Singh
2019-12-20 15:42 ` [PATCH bpf-next v1 06/13] bpf: lsm: Init Hooks and create files in securityfs KP Singh
2019-12-24 6:28 ` Andrii Nakryiko
2019-12-30 15:37 ` KP Singh
2019-12-30 18:52 ` Andrii Nakryiko
2019-12-30 19:20 ` Kees Cook
2020-01-03 23:53 ` KP Singh
2020-01-07 21:22 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 07/13] bpf: lsm: Implement attach, detach and execution KP Singh
2019-12-24 5:48 ` Andrii Nakryiko
2020-01-07 21:27 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 08/13] bpf: lsm: Show attached program names in hook read handler KP Singh
2020-01-07 21:28 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 09/13] bpf: lsm: Add a helper function bpf_lsm_event_output KP Singh
2019-12-24 6:36 ` Andrii Nakryiko
2019-12-30 15:11 ` KP Singh
2019-12-30 18:56 ` Andrii Nakryiko
2019-12-20 15:42 ` [PATCH bpf-next v1 10/13] bpf: lsm: Handle attachment of the same program KP Singh
2019-12-24 6:38 ` Andrii Nakryiko
2020-01-08 18:21 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 11/13] tools/libbpf: Add bpf_program__attach_lsm KP Singh
2019-12-24 6:44 ` Andrii Nakryiko
2020-01-08 18:24 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 12/13] bpf: lsm: Add selftests for BPF_PROG_TYPE_LSM KP Singh
2019-12-24 6:49 ` Andrii Nakryiko
2020-01-04 0:09 ` KP Singh
2020-01-09 17:59 ` Andrii Nakryiko
2020-01-08 18:25 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 13/13] bpf: lsm: Add Documentation KP Singh
2019-12-20 17:17 ` [PATCH bpf-next v1 00/13] MAC and Audit policy using eBPF (KRSI) Casey Schaufler
2019-12-20 17:38 ` KP Singh
2019-12-30 19:15 ` Kees Cook
2020-01-08 15:25 ` Stephen Smalley
2020-01-08 18:58 ` James Morris
2020-01-08 19:33 ` Stephen Smalley
2020-01-09 18:11 ` James Morris
2020-01-09 18:23 ` Greg Kroah-Hartman
2020-01-09 18:58 ` Stephen Smalley
2020-01-09 19:07 ` James Morris
2020-01-09 19:43 ` KP Singh
2020-01-09 19:47 ` Stephen Smalley
2020-01-10 15:27 ` KP Singh
2020-01-10 17:48 ` James Morris
2020-01-10 17:53 ` Alexei Starovoitov
2020-01-14 16:54 ` Stephen Smalley
2020-01-14 17:42 ` Stephen Smalley
2020-01-15 2:48 ` Alexei Starovoitov [this message]
2020-01-15 13:59 ` Stephen Smalley
2020-01-15 14:09 ` Greg Kroah-Hartman
2020-01-15 22:23 ` Alexei Starovoitov
2020-01-09 19:11 ` KP Singh
2020-01-08 18:27 ` James Morris
2019-12-20 22:46 ` Mickaël Salaün
2019-12-30 19:30 ` Kees Cook
2019-12-31 12:11 ` Mickaël Salaün
2019-12-22 1:27 ` Alexei Starovoitov
2019-12-30 14:58 ` KP Singh
2019-12-30 19:14 ` Andrii Nakryiko
2019-12-24 6:51 ` Andrii Nakryiko
2019-12-30 15:04 ` KP Singh
2019-12-30 18:58 ` Andrii Nakryiko
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