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 [thread overview]
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.
next prev parent reply other threads:[~2018-11-13 18:36 UTC|newest]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CALCETrVaPTbgycjzSB0fLUeGL=j1srUh-cL0qsKn6fw6UQgj7Q@mail.gmail.com' \
--to=luto@amacapital.net \
--cc=corbet@lwn.net \
--cc=dave.hansen@linux.intel.com \
--cc=david@fromorbit.com \
--cc=igor.stoppa@gmail.com \
--cc=igor.stoppa@huawei.com \
--cc=jmorris@namei.org \
--cc=keescook@chromium.org \
--cc=kernel-hardening@lists.openwall.com \
--cc=labbott@redhat.com \
--cc=linux-doc@vger.kernel.org \
--cc=linux-integrity@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=mhocko@kernel.org \
--cc=nadav.amit@gmail.com \
--cc=peterz@infradead.org \
--cc=rdunlap@infradead.org \
--cc=rppt@linux.vnet.ibm.com \
--cc=tglx@linutronix.de \
--cc=willy@infradead.org \
--cc=zohar@linux.vnet.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).