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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: linux-kernel@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Daniel Mack <daniel@zonque.org>,
	"David S . Miller" <davem@davemloft.net>,
	Kees Cook <keescook@chromium.org>,
	Sargun Dhillon <sargun@sargun.me>,
	kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
	linux-security-module@vger.kernel.org, netdev@vger.kernel.org,
	Tejun Heo <tj@kernel.org>,
	cgroups@vger.kernel.org
Subject: Re: [RFC v2 09/10] landlock: Handle cgroups (performance)
Date: Sat, 27 Aug 2016 11:06:44 -0700
Message-ID: <20160827180642.GA38754@ast-mbp.thefacebook.com> (raw)
In-Reply-To: <57C19E6E.6040908@digikod.net>

On Sat, Aug 27, 2016 at 04:06:38PM +0200, Mickaël Salaün wrote:
> 
> On 27/08/2016 01:05, Alexei Starovoitov wrote:
> > On Fri, Aug 26, 2016 at 05:10:40PM +0200, Mickaël Salaün wrote:
> >>
> >>>
> >>> - I don't think such 'for' loop can scale. The solution needs to work
> >>> with thousands of containers and thousands of cgroups.
> >>> In the patch 06/10 the proposal is to use 'current' as holder of
> >>> the programs:
> >>> +   for (prog = current->seccomp.landlock_prog;
> >>> +                   prog; prog = prog->prev) {
> >>> +           if (prog->filter == landlock_ret->filter) {
> >>> +                   cur_ret = BPF_PROG_RUN(prog->prog, (void *)&ctx);
> >>> +                   break;
> >>> +           }
> >>> +   }
> >>> imo that's the root of scalability issue.
> >>> I think to be able to scale the bpf programs have to be attached to
> >>> cgroups instead of tasks.
> >>> That would be very different api. seccomp doesn't need to be touched.
> >>> But that is the only way I see to be able to scale.
> >>
> >> Landlock is inspired from seccomp which also use a BPF program per
> >> thread. For seccomp, each BPF programs are executed for each syscall.
> >> For Landlock, some BPF programs are executed for some LSM hooks. I don't
> >> see why it is a scale issue for Landlock comparing to seccomp. I also
> >> don't see why storing the BPF program list pointer in the cgroup struct
> >> instead of the task struct change a lot here. The BPF programs execution
> >> will be the same anyway (for each LSM hook). Kees should probably have a
> >> better opinion on this.
> > 
> > seccomp has its own issues and copying them doesn't make this lsm any better.
> > Like seccomp bpf programs are all gigantic switch statement that looks
> > for interesting syscall numbers. All syscalls of a task are paying
> > non-trivial seccomp penalty due to such design. If bpf was attached per
> > syscall it would have been much cheaper. Of course doing it this way
> > for seccomp is not easy, but for lsm such facility is already there.
> > Blank call of a single bpf prog for all lsm hooks is unnecessary
> > overhead that can and should be avoided.
> 
> It's probably a misunderstanding. Contrary to seccomp which run all the
> thread's BPF programs for any syscall, Landlock only run eBPF programs
> for the triggered LSM hooks, if their type match. Indeed, thanks to the
> multiple eBPF program types and contrary to seccomp, Landlock only run
> an eBPF program when needed. Landlock will have almost no performance
> overhead if the syscalls do not trigger the watched LSM hooks for the
> current process.

that's not what I see in the patch 06/10:
all lsm_hooks in 'static struct security_hook_list landlock_hooks'
(which eventually means all lsm hooks) will call
static inline int landlock_hook_##NAME
which will call landlock_run_prog()
which does:
+ for (landlock_ret = current->seccomp.landlock_ret;
+      landlock_ret; landlock_ret = landlock_ret->prev) {
+    if (landlock_ret->triggered) {
+       ctx.cookie = landlock_ret->cookie;
+       for (prog = current->seccomp.landlock_prog;
+            prog; prog = prog->prev) {
+               if (prog->filter == landlock_ret->filter) {
+                       cur_ret = BPF_PROG_RUN(prog->prog, (void *)&ctx);
+                       break;
+               }
+       }

that is unacceptable overhead and not a scalable design.
It kinda works for 3 lsm_hooks as in patch 6, but doesn't scale
as soon as more lsm hooks are added.

> As said above, Landlock will not run an eBPF programs when not strictly
> needed. Attaching to a cgroup will have the same performance impact as
> attaching to a process hierarchy.

Having a prog per cgroup per lsm_hook is the only scalable way I
could come up with. If you see another way, please propose.
current->seccomp.landlock_prog is not the answer.

  reply index

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-25 10:32 [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 01/10] landlock: Add Kconfig Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 02/10] bpf: Move u64_to_ptr() to BPF headers and inline it Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 03/10] bpf,landlock: Add a new arraymap type to deal with (Landlock) handles Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 04/10] seccomp: Split put_seccomp_filter() with put_seccomp() Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 05/10] seccomp: Handle Landlock Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 06/10] landlock: Add LSM hooks Mickaël Salaün
2016-08-30 18:56   ` Andy Lutomirski
2016-08-30 20:10     ` Mickaël Salaün
2016-08-30 20:18       ` Andy Lutomirski
2016-08-30 20:27         ` Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 07/10] landlock: Add errno check Mickaël Salaün
2016-08-25 11:13   ` Andy Lutomirski
2016-08-25 10:32 ` [RFC v2 08/10] landlock: Handle file system comparisons Mickaël Salaün
2016-08-25 11:12   ` Andy Lutomirski
2016-08-25 14:10     ` Mickaël Salaün
2016-08-26 14:57       ` Andy Lutomirski
2016-08-27 13:45         ` Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 09/10] landlock: Handle cgroups Mickaël Salaün
2016-08-25 11:09   ` Andy Lutomirski
2016-08-25 14:44     ` Mickaël Salaün
2016-08-26 12:55       ` Tejun Heo
2016-08-26 14:20       ` Andy Lutomirski
2016-08-26 15:50         ` Tejun Heo
2016-08-26  2:14   ` Alexei Starovoitov
2016-08-26 15:10     ` Mickaël Salaün
2016-08-26 23:05       ` Alexei Starovoitov
2016-08-27  7:30         ` Andy Lutomirski
2016-08-27 18:11           ` Alexei Starovoitov
2016-08-28  8:14             ` Andy Lutomirski
2016-08-27 14:06         ` [RFC v2 09/10] landlock: Handle cgroups (performance) Mickaël Salaün
2016-08-27 18:06           ` Alexei Starovoitov [this message]
2016-08-27 19:35             ` Mickaël Salaün
2016-08-27 20:43               ` Alexei Starovoitov
2016-08-27 21:14                 ` Mickaël Salaün
2016-08-28  8:13                   ` Andy Lutomirski
2016-08-28  9:42                     ` Mickaël Salaün
2016-08-30 18:55                       ` Andy Lutomirski
2016-08-30 20:20                         ` Mickaël Salaün
2016-08-30 20:23                           ` Andy Lutomirski
2016-08-30 20:33                             ` Mickaël Salaün
2016-08-30 20:55                               ` Alexei Starovoitov
2016-08-30 21:45                                 ` Andy Lutomirski
2016-08-31  1:36                                   ` Alexei Starovoitov
2016-08-31  3:29                                     ` Andy Lutomirski
2016-08-27 14:19         ` [RFC v2 09/10] landlock: Handle cgroups (netfilter match) Mickaël Salaün
2016-08-27 18:32           ` Alexei Starovoitov
2016-08-27 14:34         ` [RFC v2 09/10] landlock: Handle cgroups (program types) Mickaël Salaün
2016-08-27 18:19           ` Alexei Starovoitov
2016-08-27 19:55             ` Mickaël Salaün
2016-08-27 20:56               ` Alexei Starovoitov
2016-08-27 21:18                 ` Mickaël Salaün
2016-08-25 10:32 ` [RFC v2 10/10] samples/landlock: Add sandbox example Mickaël Salaün
2016-08-25 11:05 ` [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Andy Lutomirski
2016-08-25 13:57   ` Mickaël Salaün
2016-08-27  7:40 ` Andy Lutomirski
2016-08-27 15:10   ` Mickaël Salaün
2016-08-27 15:21     ` [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing (cgroup delegation) Mickaël Salaün
2016-08-30 16:06 ` [RFC v2 00/10] Landlock LSM: Unprivileged sandboxing Andy Lutomirski
2016-08-30 19:51   ` Mickaël Salaün
2016-08-30 19:55     ` Andy Lutomirski
2016-09-15  9:19 ` Pavel Machek
2016-09-20 17:08   ` Mickaël Salaün
2016-09-24  7:45     ` Pavel Machek
2016-10-03 22:56     ` Kees Cook
2016-10-05 20:30       ` Mickaël Salaün

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