From: Andy Lutomirski <luto@amacapital.net> To: Igor Stoppa <igor.stoppa@gmail.com> Cc: Matthew Wilcox <willy@infradead.org>, Tycho Andersen <tycho@tycho.ws>, Kees Cook <keescook@chromium.org>, Peter Zijlstra <peterz@infradead.org>, Mimi Zohar <zohar@linux.vnet.ibm.com>, 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>, linux-security-module <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, 30 Oct 2018 14:02:12 -0700 Message-ID: <BAA65A07-F3AF-4209-9D18-7075CEF11EE8@amacapital.net> (raw) In-Reply-To: <9edbdf8b-b5fb-5a82-43b4-b639f5ec8484@gmail.com> > On Oct 30, 2018, at 1:43 PM, Igor Stoppa <igor.stoppa@gmail.com> wrote: > >> On 30/10/2018 21:20, Matthew Wilcox wrote: >>> On Tue, Oct 30, 2018 at 12:28:41PM -0600, Tycho Andersen wrote: >>>> On Tue, Oct 30, 2018 at 10:58:14AM -0700, Matthew Wilcox wrote: >>>> On Tue, Oct 30, 2018 at 10:06:51AM -0700, Andy Lutomirski wrote: >>>>>> On Oct 30, 2018, at 9:37 AM, Kees Cook <keescook@chromium.org> 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. >>>> >>>> I'd like to understand this approach a little better. In a syscall path, >>>> we run with the user task's mm. What you're proposing is that when we >>>> want to modify rare data, we switch to rare_mm which contains a >>>> writable mapping to all the kernel data which is rare-write. >>>> >>>> So the API might look something like this: >>>> >>>> void *p = rare_alloc(...); /* writable pointer */ >>>> p->a = x; >>>> q = rare_protect(p); /* read-only pointer */ > > With pools and memory allocated from vmap_areas, I was able to say > > protect(pool) > > and that would do a swipe on all the pages currently in use. > In the SELinux policyDB, for example, one doesn't really want to individually protect each allocation. > > The loading phase happens usually at boot, when the system can be assumed to be sane (one might even preload a bare-bone set of rules from initramfs and then replace it later on, with the full blown set). > > There is no need to process each of these tens of thousands allocations and initialization as write-rare. > > Would it be possible to do the same here? I don’t see why not, although getting the API right will be a tad complicated. > >>>> >>>> To subsequently modify q, >>>> >>>> p = rare_modify(q); >>>> q->a = y; >>> >>> Do you mean >>> >>> p->a = y; >>> >>> here? I assume the intent is that q isn't writable ever, but that's >>> the one we have in the structure at rest. >> Yes, that was my intent, thanks. >> To handle the list case that Igor has pointed out, you might want to >> do something like this: >> list_for_each_entry(x, &xs, entry) { >> struct foo *writable = rare_modify(entry); > > Would this mapping be impossible to spoof by other cores? > Indeed. Only the core with the special mm loaded could see it. But I dislike allowing regular writes in the protected region. We really only need four write primitives: 1. Just write one value. Call at any time (except NMI). 2. Just copy some bytes. Same as (1) but any number of bytes. 3,4: Same as 1 and 2 but must be called inside a special rare write region. This is purely an optimization. Actually getting a modifiable pointer should be disallowed for two reasons: 1. Some architectures may want to use a special write-different-address-space operation. Heck, x86 could, too: make the actual offset be a secret and shove the offset into FSBASE or similar. Then %fs-prefixed writes would do the rare writes. 2. Alternatively, x86 could set the U bit. Then the actual writes would use the uaccess helpers, giving extra protection via SMAP. We don’t really want a situation where an unchecked pointer in the rare write region completely defeats the mechanism.
next prev 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 [this message] 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 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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