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From: Nadav Amit <nadav.amit@gmail.com>
To: Andy Lutomirski <luto@amacapital.net>,
	Igor Stoppa <igor.stoppa@gmail.com>
Cc: 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>,
	Igor Stoppa <igor.stoppa@huawei.com>,
	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 09:43:53 -0800
Message-ID: <386C0CB1-C4B1-43E2-A754-DA8DBE4FB3CB@gmail.com> (raw)
In-Reply-To: <CALCETrXNckT9W288VXx-6inO5qYn-6dUPocKGcBT0GCO3xi3ZQ@mail.gmail.com>

From: Andy Lutomirski
Sent: November 13, 2018 at 5:16:09 PM GMT
> To: Igor Stoppa <igor.stoppa@gmail.com>
> Cc: 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>, Igor Stoppa <igor.stoppa@huawei.com>, 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
> 
> 
> On Tue, Nov 13, 2018 at 6:25 AM Igor Stoppa <igor.stoppa@gmail.com> wrote:
>> Hello,
>> I've been studying v4 of the patch-set [1] that Nadav has been working on.
>> Incidentally, I think it would be useful to cc also the
>> security/hardening ml.
>> The patch-set seems to be close to final, so I am resuming this discussion.
>> 
>> On 30/10/2018 19:06, Andy Lutomirski wrote:
>> 
>>> I support the addition of a rare-write mechanism to the upstream kernel.  And I think that there is only one sane way to implement it: using an mm_struct. That mm_struct, just like any sane mm_struct, should only differ from init_mm in that it has extra mappings in the *user* region.
>> 
>> After reading the code, I see what you meant.
>> I think I can work with it.
>> 
>> But I have a couple of questions wrt the use of this mechanism, in the
>> context of write rare.
>> 
>> 
>> 1) mm_struct.
>> 
>> Iiuc, the purpose of the patchset is mostly (only?) to patch kernel code
>> (live patch?), which seems to happen sequentially and in a relatively
>> standardized way, like replacing the NOPs specifically placed in the
>> functions that need patching.
>> 
>> This is a bit different from the more generic write-rare case, applied
>> to data.
>> 
>> As example, I have in mind a system where both IMA and SELinux are in use.
>> 
>> In this system, a file is accessed for the first time.
>> 
>> That would trigger 2 things:
>> - evaluation of the SELinux rules and probably update of the AVC cache
>> - IMA measurement and update of the measurements
>> 
>> Both of them could be write protected, meaning that they would both have
>> to be modified through the write rare mechanism.
>> 
>> While the events, for 1 specific file, would be sequential, it's not
>> difficult to imagine that multiple files could be accessed at the same time.
>> 
>> If the update of the data structures in both IMA and SELinux must use
>> the same mm_struct, that would have to be somehow regulated and it would
>> introduce an unnecessary (imho) dependency.
>> 
>> How about having one mm_struct for each writer (core or thread)?
> 
> I don't think that helps anything.  I think the mm_struct used for
> prmem (or rare_write or whatever you want to call it) 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.  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.
> 
>> 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.
> 
>> 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.

I guess that enabling IRQs might break some hidden assumptions in the code,
but is there a fundamental reason that IRQs need to be disabled? use_mm()
got them enabled, although it is only suitable for kernel threads.


  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 [this message]
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
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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