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From: Andy Lutomirski <luto@kernel.org>
To: Igor Stoppa <igor.stoppa@huawei.com>
Cc: Nadav Amit <nadav.amit@gmail.com>,
	Igor Stoppa <igor.stoppa@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Mimi Zohar <zohar@linux.vnet.ibm.com>,
	Matthew Wilcox <willy@infradead.org>,
	Dave Chinner <david@fromorbit.com>,
	James Morris <jmorris@namei.org>,
	Michal Hocko <mhocko@kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	linux-integrity <linux-integrity@vger.kernel.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Laura Abbott <labbott@redhat.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 10/17] prmem: documentation
Date: Tue, 13 Nov 2018 10:48:57 -0800
Message-ID: <CALCETrXfBePNs_bs1OroLn9Kdi91FktZ0==N7JK7e=CX=uUisg@mail.gmail.com> (raw)
In-Reply-To: <9373ccf0-f51b-4bfa-2b16-e03ebf3c670d@huawei.com>

On Tue, Nov 13, 2018 at 10:31 AM Igor Stoppa <igor.stoppa@huawei.com> wrote:
>
> On 13/11/2018 19:47, Andy Lutomirski wrote:
>
> > For general rare-writish stuff, I don't think we want IRQs running
> > with them mapped anywhere for write.  For AVC and IMA, I'm less sure.
>
> Why would these be less sensitive?

I'm not really saying they're less sensitive so much as that the
considerations are different.  I think the original rare-write code is
based on ideas from grsecurity, and it was intended to protect static
data like structs full of function pointers.   Those targets have some
different properties:

 - Static targets are at addresses that are much more guessable, so
they're easier targets for most attacks.  (Not spraying attacks like
the ones you're interested in, though.)

 - Static targets are higher value.  No offense to IMA or AVC, but
outright execution of shellcode, hijacking of control flow, or compete
disablement of core security features is higher impact than bypassing
SELinux or IMA.  Why would you bother corrupting the AVC if you could
instead just set enforcing=0?  (I suppose that corrupting the AVC is
less likely to be noticed by monitoring tools.)

 - Static targets are small.  This means that the interrupt latency
would be negligible, especially in comparison to the latency of
replacing the entire SELinux policy object.

Anyway, I'm not all that familiar with SELinux under the hood, but I'm
wondering if a different approach to thinks like the policy database
might be appropriate.  When the policy is changed, rather than
allocating rare-write memory and writing to it, what if we instead
allocated normal memory, wrote to it, write-protected it, and then
used the rare-write infrastructure to do a much smaller write to
replace the pointer?

Admittedly, this creates a window where another core could corrupt the
data as it's being written.  That may not matter so much if an
attacker can't force a policy update.  Alternatively, the update code
could re-verify the policy after write-protecting it, or there could
be a fancy API to allocate some temporarily-writable memory (by
creating a whole new mm_struct, mapping the memory writable just in
that mm_struct, and activating it) so that only the actual policy
loader could touch the memory.  But I'm mostly speculating here, since
I'm not familiar with the code in question.

Anyway, I tend to think that the right way to approach mainlining all
this is to first get the basic rare write support for static data into
place and then to build on that.  I think it's great that you're
pushing this effort, but doing this for SELinux and IMA is a bigger
project than doing it for static data, and it might make sense to do
it in bite-sized pieces.

Does any of this make sense?

  parent reply index

Thread overview: 140+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-23 21:34 [RFC v1 PATCH 00/17] prmem: protected memory Igor Stoppa
2018-10-23 21:34 ` [PATCH 01/17] prmem: linker section for static write rare Igor Stoppa
2018-10-23 21:34 ` [PATCH 02/17] prmem: write rare for static allocation Igor Stoppa
2018-10-25  0:24   ` Dave Hansen
2018-10-29 18:03     ` Igor Stoppa
2018-10-26  9:41   ` Peter Zijlstra
2018-10-29 20:01     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 03/17] prmem: vmalloc support for dynamic allocation Igor Stoppa
2018-10-25  0:26   ` Dave Hansen
2018-10-29 18:07     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 04/17] prmem: " Igor Stoppa
2018-10-23 21:34 ` [PATCH 05/17] prmem: shorthands for write rare on common types Igor Stoppa
2018-10-25  0:28   ` Dave Hansen
2018-10-29 18:12     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 06/17] prmem: test cases for memory protection Igor Stoppa
2018-10-24  3:27   ` Randy Dunlap
2018-10-24 14:24     ` Igor Stoppa
2018-10-25 16:43   ` Dave Hansen
2018-10-29 18:16     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 07/17] prmem: lkdtm tests " Igor Stoppa
2018-10-23 21:34 ` [PATCH 08/17] prmem: struct page: track vmap_area Igor Stoppa
2018-10-24  3:12   ` Matthew Wilcox
2018-10-24 23:01     ` Igor Stoppa
2018-10-25  2:13       ` Matthew Wilcox
2018-10-29 18:21         ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 09/17] prmem: hardened usercopy Igor Stoppa
2018-10-29 11:45   ` Chris von Recklinghausen
2018-10-29 18:24     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 10/17] prmem: documentation Igor Stoppa
2018-10-24  3:48   ` Randy Dunlap
2018-10-24 14:30     ` Igor Stoppa
2018-10-24 23:04   ` Mike Rapoport
2018-10-29 19:05     ` Igor Stoppa
2018-10-26  9:26   ` Peter Zijlstra
2018-10-26 10:20     ` Matthew Wilcox
2018-10-29 19:28       ` Igor Stoppa
2018-10-26 10:46     ` Kees Cook
2018-10-28 18:31       ` Peter Zijlstra
2018-10-29 21:04         ` Igor Stoppa
2018-10-30 15:26           ` Peter Zijlstra
2018-10-30 16:37             ` Kees Cook
2018-10-30 17:06               ` Andy Lutomirski
2018-10-30 17:58                 ` Matthew Wilcox
2018-10-30 18:03                   ` Dave Hansen
2018-10-31  9:18                     ` Peter Zijlstra
2018-10-30 18:28                   ` Tycho Andersen
2018-10-30 19:20                     ` Matthew Wilcox
2018-10-30 20:43                       ` Igor Stoppa
2018-10-30 21:02                         ` Andy Lutomirski
2018-10-30 21:07                           ` Kees Cook
2018-10-30 21:25                             ` Igor Stoppa
2018-10-30 22:15                           ` Igor Stoppa
2018-10-31 10:11                             ` Peter Zijlstra
2018-10-31 20:38                               ` Andy Lutomirski
2018-10-31 20:53                                 ` Andy Lutomirski
2018-10-31  9:45                           ` Peter Zijlstra
2018-10-30 21:35                         ` Matthew Wilcox
2018-10-30 21:49                           ` Igor Stoppa
2018-10-31  4:41                           ` Andy Lutomirski
2018-10-31  9:08                             ` Igor Stoppa
2018-10-31 19:38                               ` Igor Stoppa
2018-10-31 10:02                             ` Peter Zijlstra
2018-10-31 20:36                               ` Andy Lutomirski
2018-10-31 21:00                                 ` Peter Zijlstra
2018-10-31 22:57                                   ` Andy Lutomirski
2018-10-31 23:10                                     ` Igor Stoppa
2018-10-31 23:19                                       ` Andy Lutomirski
2018-10-31 23:26                                         ` Igor Stoppa
2018-11-01  8:21                                           ` Thomas Gleixner
2018-11-01 15:58                                             ` Igor Stoppa
2018-11-01 17:08                                     ` Peter Zijlstra
2018-10-30 18:51                   ` Andy Lutomirski
2018-10-30 19:14                     ` Kees Cook
2018-10-30 21:25                     ` Matthew Wilcox
2018-10-30 21:55                       ` Igor Stoppa
2018-10-30 22:08                         ` Matthew Wilcox
2018-10-31  9:29                       ` Peter Zijlstra
2018-10-30 23:18                     ` Nadav Amit
2018-10-31  9:08                       ` Peter Zijlstra
2018-11-01 16:31                         ` Nadav Amit
2018-11-02 21:11                           ` Nadav Amit
2018-10-31  9:36                   ` Peter Zijlstra
2018-10-31 11:33                     ` Matthew Wilcox
2018-11-13 14:25                 ` Igor Stoppa
2018-11-13 17:16                   ` Andy Lutomirski
2018-11-13 17:43                     ` Nadav Amit
2018-11-13 17:47                       ` Andy Lutomirski
2018-11-13 18:06                         ` Nadav Amit
2018-11-13 18:31                         ` Igor Stoppa
2018-11-13 18:33                           ` Igor Stoppa
2018-11-13 18:36                             ` Andy Lutomirski
2018-11-13 19:03                               ` Igor Stoppa
2018-11-21 16:34                               ` Igor Stoppa
2018-11-21 17:36                                 ` Nadav Amit
2018-11-21 18:01                                   ` Igor Stoppa
2018-11-21 18:15                                 ` Andy Lutomirski
2018-11-22 19:27                                   ` Igor Stoppa
2018-11-22 20:04                                     ` Matthew Wilcox
2018-11-22 20:53                                       ` Andy Lutomirski
2018-12-04 12:34                                         ` Igor Stoppa
2018-11-13 18:48                           ` Andy Lutomirski [this message]
2018-11-13 19:35                             ` Igor Stoppa
2018-11-13 18:26                     ` Igor Stoppa
2018-11-13 18:35                       ` Andy Lutomirski
2018-11-13 19:01                         ` Igor Stoppa
2018-10-31  9:27               ` Igor Stoppa
2018-10-26 11:09     ` Markus Heiser
2018-10-29 19:35       ` Igor Stoppa
2018-10-26 15:05     ` Jonathan Corbet
2018-10-29 19:38       ` Igor Stoppa
2018-10-29 20:35     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 11/17] prmem: llist: use designated initializer Igor Stoppa
2018-10-23 21:34 ` [PATCH 12/17] prmem: linked list: set alignment Igor Stoppa
2018-10-26  9:31   ` Peter Zijlstra
2018-10-23 21:35 ` [PATCH 13/17] prmem: linked list: disable layout randomization Igor Stoppa
2018-10-24 13:43   ` Alexey Dobriyan
2018-10-29 19:40     ` Igor Stoppa
2018-10-26  9:32   ` Peter Zijlstra
2018-10-26 10:17     ` Matthew Wilcox
2018-10-30 15:39       ` Peter Zijlstra
2018-10-23 21:35 ` [PATCH 14/17] prmem: llist, hlist, both plain and rcu Igor Stoppa
2018-10-24 11:37   ` Mathieu Desnoyers
2018-10-24 14:03     ` Igor Stoppa
2018-10-24 14:56       ` Tycho Andersen
2018-10-24 22:52         ` Igor Stoppa
2018-10-25  8:11           ` Tycho Andersen
2018-10-28  9:52       ` Steven Rostedt
2018-10-29 19:43         ` Igor Stoppa
2018-10-26  9:38   ` Peter Zijlstra
2018-10-23 21:35 ` [PATCH 15/17] prmem: test cases for prlist and prhlist Igor Stoppa
2018-10-23 21:35 ` [PATCH 16/17] prmem: pratomic-long Igor Stoppa
2018-10-25  0:13   ` Peter Zijlstra
2018-10-29 21:17     ` Igor Stoppa
2018-10-30 15:58       ` Peter Zijlstra
2018-10-30 16:28         ` Will Deacon
2018-10-31  9:10           ` Peter Zijlstra
2018-11-01  3:28             ` Kees Cook
2018-10-23 21:35 ` [PATCH 17/17] prmem: ima: turn the measurements list write rare Igor Stoppa
2018-10-24 23:03 ` [RFC v1 PATCH 00/17] prmem: protected memory Dave Chinner
2018-10-29 19:47   ` Igor Stoppa

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