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From: Andy Lutomirski <luto@amacapital.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	Borislav Petkov <bp@alien8.de>, Nadav Amit <nadav.amit@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Brian Gerst <brgerst@gmail.com>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>, Jann Horn <jann@thejh.net>,
	Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)
Date: Wed, 22 Jun 2016 18:22:17 -0700	[thread overview]
Message-ID: <CALCETrUuG0-tGNQ5iAEO2_gaK1eUq7AoALoBeQKcOP8cvxr=eA@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFyahpuy94qqECj0ZA6oD3Vy0r=gY2cH8_dB1a-4XURV2Q@mail.gmail.com>

On Mon, Jun 20, 2016 at 9:01 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Mon, Jun 20, 2016 at 4:43 PM, Andy Lutomirski <luto@kernel.org> wrote:
>>
>> On my laptop, this adds about 1.5µs of overhead to task creation,
>> which seems to be mainly caused by vmalloc inefficiently allocating
>> individual pages even when a higher-order page is available on the
>> freelist.
>
> I really think that problem needs to be fixed before this should be merged.
>
> The easy fix may be to just have a very limited re-use of these stacks
> in generic code, rather than try to do anything fancy with multi-page
> allocations. Just a few of these allocations held in reserve (perhaps
> make the allocations percpu to avoid new locks).

I implemented a percpu cache, and it's useless.

When a task goes away, one reference is held until the next RCU grace
period so that task_struct can be used under RCU (look for
delayed_put_task_struct).  This means that free_task gets called in
giant batches under heavy clone() load, which is the only time that
any of this matters, which means that only get to refill the cache
once per RCU batch, which means that there's very little benefit.

Once thread_info stops living in the stack, we could, in principle,
exempt the stack itself from RCU protection, thus saving a bit of
memory under load and making the cache work.  I've started working on
(optionally, per-arch) getting rid of on-stack thread_info, but that's
not ready yet.

FWIW, the same issue quite possibly hurts non-vmap-stack performance
as well, as it makes it much less likely that a cache-hot stack gets
immediately reused under heavy fork load.

So may I skip this for now?  I think that the performance hit is
unlikely to matter on most workloads, and I also expect the speedup
from not using higher-order allocations to be a decent win on some
workloads.

--Andy

WARNING: multiple messages have this Message-ID (diff)
From: Andy Lutomirski <luto@amacapital.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	Borislav Petkov <bp@alien8.de>, Nadav Amit <nadav.amit@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Brian Gerst <brgerst@gmail.com>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>, Jann Horn <jann@thejh.net>,
	Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: [kernel-hardening] Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)
Date: Wed, 22 Jun 2016 18:22:17 -0700	[thread overview]
Message-ID: <CALCETrUuG0-tGNQ5iAEO2_gaK1eUq7AoALoBeQKcOP8cvxr=eA@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFyahpuy94qqECj0ZA6oD3Vy0r=gY2cH8_dB1a-4XURV2Q@mail.gmail.com>

On Mon, Jun 20, 2016 at 9:01 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Mon, Jun 20, 2016 at 4:43 PM, Andy Lutomirski <luto@kernel.org> wrote:
>>
>> On my laptop, this adds about 1.5µs of overhead to task creation,
>> which seems to be mainly caused by vmalloc inefficiently allocating
>> individual pages even when a higher-order page is available on the
>> freelist.
>
> I really think that problem needs to be fixed before this should be merged.
>
> The easy fix may be to just have a very limited re-use of these stacks
> in generic code, rather than try to do anything fancy with multi-page
> allocations. Just a few of these allocations held in reserve (perhaps
> make the allocations percpu to avoid new locks).

I implemented a percpu cache, and it's useless.

When a task goes away, one reference is held until the next RCU grace
period so that task_struct can be used under RCU (look for
delayed_put_task_struct).  This means that free_task gets called in
giant batches under heavy clone() load, which is the only time that
any of this matters, which means that only get to refill the cache
once per RCU batch, which means that there's very little benefit.

Once thread_info stops living in the stack, we could, in principle,
exempt the stack itself from RCU protection, thus saving a bit of
memory under load and making the cache work.  I've started working on
(optionally, per-arch) getting rid of on-stack thread_info, but that's
not ready yet.

FWIW, the same issue quite possibly hurts non-vmap-stack performance
as well, as it makes it much less likely that a cache-hot stack gets
immediately reused under heavy fork load.

So may I skip this for now?  I think that the performance hit is
unlikely to matter on most workloads, and I also expect the speedup
from not using higher-order allocations to be a decent win on some
workloads.

--Andy

  parent reply	other threads:[~2016-06-23  1:22 UTC|newest]

Thread overview: 269+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-20 23:43 [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Andy Lutomirski
2016-06-20 23:43 ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43 ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 01/13] x86/mm/hotplug: Don't remove PGD entries in remove_pagetable() Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 02/13] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 03/13] x86/mm: Remove kernel_unmap_pages_in_pgd() and efi_cleanup_page_tables() Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  9:53   ` Matt Fleming
2016-06-21  9:53     ` [kernel-hardening] " Matt Fleming
2016-06-21  9:53     ` Matt Fleming
2016-06-20 23:43 ` [PATCH v3 04/13] mm: Track NR_KERNEL_STACK in KiB instead of number of stacks Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  9:46   ` Vladimir Davydov
2016-06-21  9:46     ` [kernel-hardening] " Vladimir Davydov
2016-06-21  9:46     ` Vladimir Davydov
2016-06-21  9:46     ` Vladimir Davydov
2016-06-22  7:35   ` Michal Hocko
2016-06-22  7:35     ` [kernel-hardening] " Michal Hocko
2016-06-22  7:35     ` Michal Hocko
2016-06-22  7:35     ` Michal Hocko
2016-06-20 23:43 ` [PATCH v3 05/13] mm: Fix memcg stack accounting for sub-page stacks Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  9:54   ` Vladimir Davydov
2016-06-21  9:54     ` [kernel-hardening] " Vladimir Davydov
2016-06-21  9:54     ` Vladimir Davydov
2016-06-21  9:54     ` Vladimir Davydov
2016-06-22  7:38   ` Michal Hocko
2016-06-22  7:38     ` [kernel-hardening] " Michal Hocko
2016-06-22  7:38     ` Michal Hocko
2016-06-22  7:38     ` Michal Hocko
2016-06-20 23:43 ` [PATCH v3 06/13] fork: Add generic vmalloced stack support Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  7:30   ` Jann Horn
2016-06-21  7:30     ` [kernel-hardening] " Jann Horn
2016-06-21  7:30     ` Jann Horn
2016-06-21 16:59     ` Andy Lutomirski
2016-06-21 16:59       ` [kernel-hardening] " Andy Lutomirski
2016-06-21 16:59       ` Andy Lutomirski
2016-06-21 17:13       ` Kees Cook
2016-06-21 17:13         ` [kernel-hardening] " Kees Cook
2016-06-21 17:13         ` Kees Cook
2016-06-21 17:28         ` Andy Lutomirski
2016-06-21 17:28           ` [kernel-hardening] " Andy Lutomirski
2016-06-21 17:28           ` Andy Lutomirski
2016-06-21 18:32         ` [kernel-hardening] " Rik van Riel
2016-06-21 18:32           ` Rik van Riel
2016-06-21 19:44           ` [kernel-hardening] " Arnd Bergmann
2016-06-21 19:44             ` Arnd Bergmann
2016-06-21 19:43             ` [kernel-hardening] " Andy Lutomirski
2016-06-21 19:43               ` Andy Lutomirski
2016-06-21 19:43               ` Andy Lutomirski
2016-07-11 17:00           ` [kernel-hardening] " Andrey Ryabinin
2016-06-20 23:43 ` [PATCH v3 07/13] x86/die: Don't try to recover from an OOPS on a non-default stack Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 08/13] x86/dumpstack: When OOPSing, rewind the stack before do_exit Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 09/13] x86/dumpstack: When dumping stack bytes due to OOPS, start with regs->sp Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 10/13] x86/dumpstack: Try harder to get a call trace on stack overflow Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 11/13] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 12/13] x86/mm/64: Enable vmapped stacks Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 13/13] x86/mm: Improve stack-overflow #PF handling Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  4:01 ` [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Linus Torvalds
2016-06-21  4:01   ` [kernel-hardening] " Linus Torvalds
2016-06-21  4:01   ` Linus Torvalds
2016-06-21 16:45   ` Andy Lutomirski
2016-06-21 16:45     ` [kernel-hardening] " Andy Lutomirski
2016-06-21 16:45     ` Andy Lutomirski
2016-06-21 17:16     ` Linus Torvalds
2016-06-21 17:16       ` [kernel-hardening] " Linus Torvalds
2016-06-21 17:16       ` Linus Torvalds
2016-06-21 17:27       ` Andy Lutomirski
2016-06-21 17:27         ` [kernel-hardening] " Andy Lutomirski
2016-06-21 17:27         ` Andy Lutomirski
2016-06-21 18:12         ` Kees Cook
2016-06-21 18:12           ` [kernel-hardening] " Kees Cook
2016-06-21 18:12           ` Kees Cook
2016-06-21 18:19           ` [kernel-hardening] " Rik van Riel
2016-06-21 18:19             ` Rik van Riel
2016-06-23  1:22   ` Andy Lutomirski [this message]
2016-06-23  1:22     ` [kernel-hardening] " Andy Lutomirski
2016-06-23  1:22     ` Andy Lutomirski
2016-06-23  6:02     ` Linus Torvalds
2016-06-23  6:02       ` [kernel-hardening] " Linus Torvalds
2016-06-23  6:02       ` Linus Torvalds
2016-06-23 14:31       ` Oleg Nesterov
2016-06-23 14:31         ` [kernel-hardening] " Oleg Nesterov
2016-06-23 14:31         ` Oleg Nesterov
2016-06-23 16:30         ` Linus Torvalds
2016-06-23 16:30           ` [kernel-hardening] " Linus Torvalds
2016-06-23 16:30           ` Linus Torvalds
2016-06-23 16:41           ` Andy Lutomirski
2016-06-23 16:41             ` [kernel-hardening] " Andy Lutomirski
2016-06-23 16:41             ` Andy Lutomirski
2016-06-23 17:10             ` Oleg Nesterov
2016-06-23 17:10               ` [kernel-hardening] " Oleg Nesterov
2016-06-23 17:10               ` Oleg Nesterov
2016-09-06 16:19             ` Jann Horn
2016-09-06 16:19               ` [kernel-hardening] " Jann Horn
2016-09-06 16:19               ` Jann Horn
2016-09-06 16:40               ` Andy Lutomirski
2016-09-06 16:40                 ` [kernel-hardening] " Andy Lutomirski
2016-09-06 16:40                 ` Andy Lutomirski
2016-06-23 17:03           ` Oleg Nesterov
2016-06-23 17:03             ` [kernel-hardening] " Oleg Nesterov
2016-06-23 17:03             ` Oleg Nesterov
2016-06-23 17:44             ` Linus Torvalds
2016-06-23 17:44               ` [kernel-hardening] " Linus Torvalds
2016-06-23 17:44               ` Linus Torvalds
2016-06-23 17:52               ` Linus Torvalds
2016-06-23 17:52                 ` [kernel-hardening] " Linus Torvalds
2016-06-23 17:52                 ` Linus Torvalds
2016-06-23 18:00                 ` Kees Cook
2016-06-23 18:00                   ` [kernel-hardening] " Kees Cook
2016-06-23 18:00                   ` Kees Cook
2016-06-23 18:54                   ` Peter Zijlstra
2016-06-23 18:54                     ` [kernel-hardening] " Peter Zijlstra
2016-06-23 18:54                     ` Peter Zijlstra
2016-06-23 18:12                 ` Oleg Nesterov
2016-06-23 18:12                   ` [kernel-hardening] " Oleg Nesterov
2016-06-23 18:12                   ` Oleg Nesterov
2016-06-23 18:55                   ` Peter Zijlstra
2016-06-23 18:55                     ` [kernel-hardening] " Peter Zijlstra
2016-06-23 18:55                     ` Peter Zijlstra
2016-06-23 18:46                 ` Linus Torvalds
2016-06-23 18:46                   ` [kernel-hardening] " Linus Torvalds
2016-06-23 18:46                   ` Linus Torvalds
2016-06-23 19:08                   ` Andy Lutomirski
2016-06-23 19:08                     ` [kernel-hardening] " Andy Lutomirski
2016-06-23 19:08                     ` Andy Lutomirski
2016-06-23 18:53                 ` Peter Zijlstra
2016-06-23 18:53                   ` [kernel-hardening] " Peter Zijlstra
2016-06-23 18:53                   ` Peter Zijlstra
2016-06-23 19:09                   ` Andy Lutomirski
2016-06-23 19:09                     ` [kernel-hardening] " Andy Lutomirski
2016-06-23 19:09                     ` Andy Lutomirski
2016-06-23 19:13                     ` Peter Zijlstra
2016-06-23 19:13                       ` [kernel-hardening] " Peter Zijlstra
2016-06-23 19:13                       ` Peter Zijlstra
2016-06-23 19:17                   ` Linus Torvalds
2016-06-23 19:17                     ` [kernel-hardening] " Linus Torvalds
2016-06-23 19:17                     ` Linus Torvalds
2016-06-24  6:17                     ` Linus Torvalds
2016-06-24  6:17                       ` [kernel-hardening] " Linus Torvalds
2016-06-24  6:17                       ` Linus Torvalds
2016-06-24 12:25                       ` Brian Gerst
2016-06-24 12:25                         ` [kernel-hardening] " Brian Gerst
2016-06-24 12:25                         ` Brian Gerst
2016-06-24 17:21                         ` Linus Torvalds
2016-06-24 17:21                           ` [kernel-hardening] " Linus Torvalds
2016-06-24 17:21                           ` Linus Torvalds
2016-06-24 17:40                           ` Linus Torvalds
2016-06-24 17:40                             ` [kernel-hardening] " Linus Torvalds
2016-06-24 17:40                             ` Linus Torvalds
2016-06-24 17:47                             ` Andy Lutomirski
2016-06-24 17:47                               ` [kernel-hardening] " Andy Lutomirski
2016-06-24 17:47                               ` Andy Lutomirski
2016-06-24 17:56                               ` Linus Torvalds
2016-06-24 17:56                                 ` [kernel-hardening] " Linus Torvalds
2016-06-24 17:56                                 ` Linus Torvalds
2016-06-24 18:36                                 ` Andy Lutomirski
2016-06-24 18:36                                   ` [kernel-hardening] " Andy Lutomirski
2016-06-24 18:36                                   ` Andy Lutomirski
2016-06-24 17:51                             ` Linus Torvalds
2016-06-24 17:51                               ` [kernel-hardening] " Linus Torvalds
2016-06-24 17:51                               ` Linus Torvalds
2016-06-24 18:11                               ` Linus Torvalds
2016-06-24 18:11                                 ` [kernel-hardening] " Linus Torvalds
2016-06-24 18:11                                 ` Linus Torvalds
2016-06-24 20:25                                 ` Josh Poimboeuf
2016-06-24 20:25                                   ` [kernel-hardening] " Josh Poimboeuf
2016-06-24 20:25                                   ` Josh Poimboeuf
2016-06-24 20:51                                   ` Josh Poimboeuf
2016-06-24 20:51                                     ` [kernel-hardening] " Josh Poimboeuf
2016-06-24 20:51                                     ` Josh Poimboeuf
2016-06-24 20:53                                     ` Andy Lutomirski
2016-06-24 20:53                                       ` [kernel-hardening] " Andy Lutomirski
2016-06-24 20:53                                       ` Andy Lutomirski
2016-06-24 21:06                                     ` Linus Torvalds
2016-06-24 21:06                                       ` [kernel-hardening] " Linus Torvalds
2016-06-24 21:06                                       ` Linus Torvalds
2016-06-24 21:25                                       ` Andy Lutomirski
2016-06-24 21:25                                         ` [kernel-hardening] " Andy Lutomirski
2016-06-24 21:25                                         ` Andy Lutomirski
2016-06-24 21:32                                         ` Linus Torvalds
2016-06-24 21:32                                           ` [kernel-hardening] " Linus Torvalds
2016-06-24 21:32                                           ` Linus Torvalds
2016-06-24 21:34                                           ` Andy Lutomirski
2016-06-24 21:34                                             ` [kernel-hardening] " Andy Lutomirski
2016-06-24 21:34                                             ` Andy Lutomirski
2016-06-25  2:41                                             ` Linus Torvalds
2016-06-25  2:41                                               ` [kernel-hardening] " Linus Torvalds
2016-06-25  2:41                                               ` Linus Torvalds
2016-06-25 23:19                                               ` Andy Lutomirski
2016-06-25 23:19                                                 ` [kernel-hardening] " Andy Lutomirski
2016-06-25 23:19                                                 ` Andy Lutomirski
2016-06-25 23:30                                                 ` Andy Lutomirski
2016-06-25 23:30                                                   ` [kernel-hardening] " Andy Lutomirski
2016-06-25 23:30                                                   ` Andy Lutomirski
2016-06-26  1:23                                                   ` Linus Torvalds
2016-06-26  1:23                                                     ` [kernel-hardening] " Linus Torvalds
2016-06-26  1:23                                                     ` Linus Torvalds
2016-06-23 18:52               ` Oleg Nesterov
2016-06-23 18:52                 ` [kernel-hardening] " Oleg Nesterov
2016-06-23 18:52                 ` Oleg Nesterov
2016-06-24 14:05                 ` Michal Hocko
2016-06-24 14:05                   ` [kernel-hardening] " Michal Hocko
2016-06-24 14:05                   ` Michal Hocko
2016-06-24 15:06                   ` Michal Hocko
2016-06-24 15:06                     ` [kernel-hardening] " Michal Hocko
2016-06-24 15:06                     ` Michal Hocko
2016-06-24 15:06                     ` Michal Hocko
2016-06-24 20:22                     ` Oleg Nesterov
2016-06-24 20:22                       ` [kernel-hardening] " Oleg Nesterov
2016-06-24 20:22                       ` Oleg Nesterov
2016-06-27 10:36                       ` Michal Hocko
2016-06-27 10:36                         ` [kernel-hardening] " Michal Hocko
2016-06-27 10:36                         ` Michal Hocko
2016-06-23 19:11         ` Peter Zijlstra
2016-06-23 19:11           ` [kernel-hardening] " Peter Zijlstra
2016-06-23 19:11           ` Peter Zijlstra
2016-06-23 19:34           ` Linus Torvalds
2016-06-23 19:34             ` [kernel-hardening] " Linus Torvalds
2016-06-23 19:34             ` Linus Torvalds
2016-06-23 19:46             ` Peter Zijlstra
2016-06-23 19:46               ` [kernel-hardening] " Peter Zijlstra
2016-06-23 19:46               ` Peter Zijlstra
2016-06-21  9:24 ` Arnd Bergmann
2016-06-21  9:24   ` [kernel-hardening] " Arnd Bergmann
2016-06-21  9:24   ` Arnd Bergmann
2016-06-21 17:16   ` Kees Cook
2016-06-21 17:16     ` [kernel-hardening] " Kees Cook
2016-06-21 17:16     ` Kees Cook
2016-06-21 18:02     ` [kernel-hardening] " Rik van Riel
2016-06-21 18:02       ` Rik van Riel
2016-06-21 18:05       ` [kernel-hardening] " Andy Lutomirski
2016-06-21 18:05         ` Andy Lutomirski
2016-06-21 18:05         ` Andy Lutomirski
2016-06-21 19:47     ` Arnd Bergmann
2016-06-21 19:47       ` [kernel-hardening] " Arnd Bergmann
2016-06-21 19:47       ` Arnd Bergmann
2016-06-21 19:47       ` Andy Lutomirski
2016-06-21 19:47         ` [kernel-hardening] " Andy Lutomirski
2016-06-21 19:47         ` Andy Lutomirski
2016-06-21 20:18         ` Kees Cook
2016-06-21 20:18           ` [kernel-hardening] " Kees Cook
2016-06-21 20:18           ` Kees Cook

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