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From: Andy Lutomirski <luto@amacapital.net>
To: Igor Stoppa <igor.stoppa@huawei.com>
Cc: Igor Stoppa <igor.stoppa@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Nadav Amit <nadav.amit@gmail.com>,
	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 10:35:53 -0800
Message-ID: <CALCETrVaPTbgycjzSB0fLUeGL=j1srUh-cL0qsKn6fw6UQgj7Q@mail.gmail.com> (raw)
In-Reply-To: <17a007eb-43ea-e4da-b066-0d8c502f5f6e@huawei.com>

On Tue, Nov 13, 2018 at 10:26 AM Igor Stoppa <igor.stoppa@huawei.com> wrote:
>
> On 13/11/2018 19:16, Andy Lutomirski wrote:
>
> > should be
> > entirely abstracted away by an appropriate API, so neither SELinux nor
> > IMA need to be aware that there's an mm_struct involved.
>
> Yes, that is fine. In my proposal I was thinking about tying it to the
> core/thread that performs the actual write.
>
> The high level API could be something like:
>
> wr_memcpy(void *src, void *dst, uint_t size)
>
> >  It's also
> > entirely possible that some architectures won't even use an mm_struct
> > behind the scenes -- x86, for example, could have avoided it if there
> > were a kernel equivalent of PKRU.  Sadly, there isn't.
>
> The mm_struct - or whatever is the means to do the write on that
> architecture - can be kept hidden from the API.
>
> But the reason why I was proposing to have one mm_struct per writer is
> that, iiuc, the secondary mapping is created in the secondary mm_struct
> for each writer using it.
>
> So the updating of IMA measurements would have, theoretically, also
> write access to the SELinux AVC. Which I was trying to avoid.
> And similarly any other write rare updater. Is this correct?

If you call a wr_memcpy() function with the signature you suggested,
then you can overwrite any memory of this type.  Having a different
mm_struct under the hood makes no difference.  As far as I'm
concerned, for *dynamically allocated* rare-writable memory, you might
as well allocate all the paging structures at the same time, so the
mm_struct will always contain the mappings.  If there are serious bugs
in wr_memcpy() that cause it to write to the wrong place, we have
bigger problems.

I can imagine that we'd want a *typed* wr_memcpy()-like API some day,
but that can wait for v2.  And it still doesn't obviously need
multiple mm_structs.

>
> >> 2) Iiuc, the purpose of the 2 pages being remapped is that the target of
> >> the patch might spill across the page boundary, however if I deal with
> >> the modification of generic data, I shouldn't (shouldn't I?) assume that
> >> the data will not span across multiple pages.
> >
> > The reason for the particular architecture of text_poke() is to avoid
> > memory allocation to get it working.  i think that prmem/rare_write
> > should have each rare-writable kernel address map to a unique user
> > address, possibly just by offsetting everything by a constant.  For
> > rare_write, you don't actually need it to work as such until fairly
> > late in boot, since the rare_writable data will just be writable early
> > on.
>
> Yes, that is true. I think it's safe to assume, from an attack pattern,
> that as long as user space is not started, the system can be considered
> ok. Even user-space code run from initrd should be ok, since it can be
> bundled (and signed) as a single binary with the kernel.
>
> Modules loaded from a regular filesystem are a bit more risky, because
> an attack might inject a rogue key in the key-ring and use it to load
> malicious modules.

If a malicious module is loaded, the game is over.

>
> >> If the data spans across multiple pages, in unknown amount, I suppose
> >> that I should not keep interrupts disabled for an unknown time, as it
> >> would hurt preemption.
> >>
> >> What I thought, in my initial patch-set, was to iterate over each page
> >> that must be written to, in a loop, re-enabling interrupts in-between
> >> iterations, to give pending interrupts a chance to be served.
> >>
> >> This would mean that the data being written to would not be consistent,
> >> but it's a problem that would have to be addressed anyways, since it can
> >> be still read by other cores, while the write is ongoing.
> >
> > This probably makes sense, except that enabling and disabling
> > interrupts means you also need to restore the original mm_struct (most
> > likely), which is slow.  I don't think there's a generic way to check
> > whether in interrupt is pending without turning interrupts on.
>
> The only "excuse" I have is that write_rare is opt-in and is "rare".
> Maybe the enabling/disabling of interrupts - and the consequent switch
> of mm_struct - could be somehow tied to the latency configuration?
>
> If preemption is disabled, the expectations on the system latency are
> anyway more relaxed.
>
> But I'm not sure how it would work against I/O.

I think it's entirely reasonable for the API to internally break up
very large memcpys.

  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
2018-11-13 19:35                             ` Igor Stoppa
2018-11-13 18:26                     ` Igor Stoppa
2018-11-13 18:35                       ` Andy Lutomirski [this message]
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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