From: Thomas Gleixner <tglx@linutronix.de> To: Andy Lutomirski <luto@kernel.org> Cc: Mathias Krause <minipli@googlemail.com>, Kees Cook <keescook@chromium.org>, "kernel-hardening@lists.openwall.com" <kernel-hardening@lists.openwall.com>, Mark Rutland <mark.rutland@arm.com>, Hoeun Ryu <hoeun.ryu@gmail.com>, PaX Team <pageexec@freemail.hu>, Emese Revfy <re.emese@gmail.com>, Russell King <linux@armlinux.org.uk>, X86 ML <x86@kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, Peter Zijlstra <peterz@infradead.org> Subject: Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Date: Fri, 7 Apr 2017 22:44:39 +0200 (CEST) [thread overview] Message-ID: <alpine.DEB.2.20.1704072125460.1958@nanos> (raw) In-Reply-To: <CALCETrWuZPDjAuE1jnhJNKiZOOEdbus-O6GY8++0UO56Q84PZw@mail.gmail.com> On Fri, 7 Apr 2017, Andy Lutomirski wrote: > On Fri, Apr 7, 2017 at 6:30 AM, Mathias Krause <minipli@googlemail.com> wrote: > > On 7 April 2017 at 15:14, Thomas Gleixner <tglx@linutronix.de> wrote: > >> I really do not care whether PaX wants to chase and verify that over and > >> over. I certainly don't want to take the chance to leak CR0.WP ever and I > >> very much care about extra stuff to check in the entry/exit path. > > > > Fair enough. However, placing a BUG_ON(!(read_cr0() & X86_CR0_WP)) > > somewhere sensible should make those "leaks" visible fast -- and their > > exploitation impossible, i.e. fail hard. > > The leaks surely exist and now we'll just add an exploitable BUG. :) > I think we're approaching this all wrong, actually. The fact that x86 > has this CR0.WP thing is arguably a historical accident, and the fact > that PaX uses it doesn't mean that PaX is doing it the best way for > upstream Linux. As I said before. It should be fused to 1. > Why don't we start at the other end and do a generic non-arch-specific > implementation: set up an mm_struct that contains an RW alias of the > relevant parts of rodata and use use_mm to access it. (That is, > get_fs() to back up the old fs, set_fs(USER_DS), > use_mm(&rare_write_mm), do the write using copy_to_user, undo > everything.) That works too, though I'm not sure that it's more efficient than temporarily creating and undoing a single cpu local alias mapping similar to the kmap_atomic mechanism in the highmem case. Aside of that the alias mapping requires a full PGDIR entry unless you want to get into the mess of keeping yet another identity mapping up to date. Thanks, tglx
WARNING: multiple messages have this Message-ID (diff)
From: tglx@linutronix.de (Thomas Gleixner) To: linux-arm-kernel@lists.infradead.org Subject: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Date: Fri, 7 Apr 2017 22:44:39 +0200 (CEST) [thread overview] Message-ID: <alpine.DEB.2.20.1704072125460.1958@nanos> (raw) In-Reply-To: <CALCETrWuZPDjAuE1jnhJNKiZOOEdbus-O6GY8++0UO56Q84PZw@mail.gmail.com> On Fri, 7 Apr 2017, Andy Lutomirski wrote: > On Fri, Apr 7, 2017 at 6:30 AM, Mathias Krause <minipli@googlemail.com> wrote: > > On 7 April 2017 at 15:14, Thomas Gleixner <tglx@linutronix.de> wrote: > >> I really do not care whether PaX wants to chase and verify that over and > >> over. I certainly don't want to take the chance to leak CR0.WP ever and I > >> very much care about extra stuff to check in the entry/exit path. > > > > Fair enough. However, placing a BUG_ON(!(read_cr0() & X86_CR0_WP)) > > somewhere sensible should make those "leaks" visible fast -- and their > > exploitation impossible, i.e. fail hard. > > The leaks surely exist and now we'll just add an exploitable BUG. :) > I think we're approaching this all wrong, actually. The fact that x86 > has this CR0.WP thing is arguably a historical accident, and the fact > that PaX uses it doesn't mean that PaX is doing it the best way for > upstream Linux. As I said before. It should be fused to 1. > Why don't we start at the other end and do a generic non-arch-specific > implementation: set up an mm_struct that contains an RW alias of the > relevant parts of rodata and use use_mm to access it. (That is, > get_fs() to back up the old fs, set_fs(USER_DS), > use_mm(&rare_write_mm), do the write using copy_to_user, undo > everything.) That works too, though I'm not sure that it's more efficient than temporarily creating and undoing a single cpu local alias mapping similar to the kmap_atomic mechanism in the highmem case. Aside of that the alias mapping requires a full PGDIR entry unless you want to get into the mess of keeping yet another identity mapping up to date. Thanks, tglx
next prev parent reply other threads:[~2017-04-07 20:45 UTC|newest] Thread overview: 188+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-29 18:15 [RFC v2] Introduce rare_write() infrastructure Kees Cook 2017-03-29 18:15 ` [kernel-hardening] " Kees Cook 2017-03-29 18:15 ` Kees Cook 2017-03-29 18:15 ` [RFC v2][PATCH 01/11] " Kees Cook 2017-03-29 18:15 ` [kernel-hardening] " Kees Cook 2017-03-29 18:15 ` Kees Cook 2017-03-29 18:23 ` Kees Cook 2017-03-29 18:23 ` [kernel-hardening] " Kees Cook 2017-03-29 18:23 ` Kees Cook 2017-03-30 7:44 ` Ho-Eun Ryu 2017-03-30 7:44 ` [kernel-hardening] " Ho-Eun Ryu 2017-03-30 7:44 ` Ho-Eun Ryu 2017-03-30 17:02 ` Kees Cook 2017-03-30 17:02 ` [kernel-hardening] " Kees Cook 2017-03-30 17:02 ` Kees Cook 2017-04-07 8:09 ` Ho-Eun Ryu 2017-04-07 8:09 ` [kernel-hardening] " Ho-Eun Ryu 2017-04-07 8:09 ` Ho-Eun Ryu 2017-04-07 20:38 ` Kees Cook 2017-04-07 20:38 ` [kernel-hardening] " Kees Cook 2017-04-07 20:38 ` Kees Cook 2017-03-29 18:15 ` [RFC v2][PATCH 02/11] lkdtm: add test for " Kees Cook 2017-03-29 18:15 ` [kernel-hardening] " Kees Cook 2017-03-29 18:15 ` Kees Cook 2017-03-30 9:34 ` [kernel-hardening] " Ian Campbell 2017-03-30 9:34 ` Ian Campbell 2017-03-30 16:16 ` Kees Cook 2017-03-30 16:16 ` Kees Cook 2017-03-30 16:16 ` Kees Cook 2017-03-29 18:15 ` [RFC v2][PATCH 03/11] net: switch sock_diag handlers to rare_write() Kees Cook 2017-03-29 18:15 ` [kernel-hardening] " Kees Cook 2017-03-29 18:15 ` Kees Cook 2017-03-29 18:15 ` [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Kees Cook 2017-03-29 18:15 ` [kernel-hardening] " Kees Cook 2017-03-29 18:15 ` Kees Cook 2017-03-29 22:38 ` Andy Lutomirski 2017-03-29 22:38 ` [kernel-hardening] " Andy Lutomirski 2017-03-29 22:38 ` Andy Lutomirski 2017-03-30 1:41 ` Kees Cook 2017-03-30 1:41 ` [kernel-hardening] " Kees Cook 2017-03-30 1:41 ` Kees Cook 2017-04-05 23:57 ` Andy Lutomirski 2017-04-05 23:57 ` [kernel-hardening] " Andy Lutomirski 2017-04-05 23:57 ` Andy Lutomirski 2017-04-06 0:14 ` Kees Cook 2017-04-06 0:14 ` [kernel-hardening] " Kees Cook 2017-04-06 0:14 ` Kees Cook 2017-04-06 15:59 ` Andy Lutomirski 2017-04-06 15:59 ` [kernel-hardening] " Andy Lutomirski 2017-04-06 15:59 ` Andy Lutomirski 2017-04-07 8:34 ` [kernel-hardening] " Mathias Krause 2017-04-07 8:34 ` Mathias Krause 2017-04-07 8:34 ` Mathias Krause 2017-04-07 9:46 ` Thomas Gleixner 2017-04-07 9:46 ` Thomas Gleixner 2017-04-07 9:46 ` Thomas Gleixner 2017-04-07 10:51 ` Mathias Krause 2017-04-07 10:51 ` Mathias Krause 2017-04-07 10:51 ` Mathias Krause 2017-04-07 13:14 ` Thomas Gleixner 2017-04-07 13:14 ` Thomas Gleixner 2017-04-07 13:14 ` Thomas Gleixner 2017-04-07 13:30 ` Mathias Krause 2017-04-07 13:30 ` Mathias Krause 2017-04-07 13:30 ` Mathias Krause 2017-04-07 16:14 ` Andy Lutomirski 2017-04-07 16:14 ` Andy Lutomirski 2017-04-07 16:14 ` Andy Lutomirski 2017-04-07 16:22 ` Mark Rutland 2017-04-07 16:22 ` Mark Rutland 2017-04-07 16:22 ` Mark Rutland 2017-04-07 19:58 ` PaX Team 2017-04-07 19:58 ` PaX Team 2017-04-07 19:58 ` PaX Team 2017-04-08 4:58 ` Andy Lutomirski 2017-04-08 4:58 ` Andy Lutomirski 2017-04-08 4:58 ` Andy Lutomirski 2017-04-09 12:47 ` PaX Team 2017-04-09 12:47 ` PaX Team 2017-04-09 12:47 ` PaX Team 2017-04-10 0:10 ` Andy Lutomirski 2017-04-10 0:10 ` Andy Lutomirski 2017-04-10 0:10 ` Andy Lutomirski 2017-04-10 10:42 ` PaX Team 2017-04-10 10:42 ` PaX Team 2017-04-10 10:42 ` PaX Team 2017-04-10 16:01 ` Andy Lutomirski 2017-04-10 16:01 ` Andy Lutomirski 2017-04-10 16:01 ` Andy Lutomirski 2017-04-07 20:44 ` Thomas Gleixner [this message] 2017-04-07 20:44 ` Thomas Gleixner 2017-04-07 20:44 ` Thomas Gleixner 2017-04-07 21:20 ` Kees Cook 2017-04-07 21:20 ` Kees Cook 2017-04-07 21:20 ` Kees Cook 2017-04-08 4:12 ` Daniel Micay 2017-04-08 4:12 ` Daniel Micay 2017-04-08 4:12 ` Daniel Micay 2017-04-08 4:13 ` Daniel Micay 2017-04-08 4:13 ` Daniel Micay 2017-04-08 4:13 ` Daniel Micay 2017-04-08 4:21 ` Daniel Micay 2017-04-08 4:21 ` Daniel Micay 2017-04-08 4:21 ` Daniel Micay 2017-04-08 5:07 ` Andy Lutomirski 2017-04-08 5:07 ` Andy Lutomirski 2017-04-08 5:07 ` Andy Lutomirski 2017-04-08 7:33 ` Daniel Micay 2017-04-08 7:33 ` Daniel Micay 2017-04-08 7:33 ` Daniel Micay 2017-04-08 15:20 ` Andy Lutomirski 2017-04-08 15:20 ` Andy Lutomirski 2017-04-08 15:20 ` Andy Lutomirski 2017-04-09 10:53 ` Ingo Molnar 2017-04-09 10:53 ` Ingo Molnar 2017-04-09 10:53 ` Ingo Molnar 2017-04-10 10:22 ` Mark Rutland 2017-04-10 10:22 ` Mark Rutland 2017-04-10 10:22 ` Mark Rutland 2017-04-09 20:24 ` PaX Team 2017-04-09 20:24 ` PaX Team 2017-04-09 20:24 ` PaX Team 2017-04-10 0:31 ` Andy Lutomirski 2017-04-10 0:31 ` Andy Lutomirski 2017-04-10 0:31 ` Andy Lutomirski 2017-04-10 19:47 ` PaX Team 2017-04-10 19:47 ` PaX Team 2017-04-10 19:47 ` PaX Team 2017-04-10 20:27 ` Andy Lutomirski 2017-04-10 20:27 ` Andy Lutomirski 2017-04-10 20:27 ` Andy Lutomirski 2017-04-10 20:13 ` Kees Cook 2017-04-10 20:13 ` Kees Cook 2017-04-10 20:13 ` Kees Cook 2017-04-10 20:17 ` Andy Lutomirski 2017-04-10 20:17 ` Andy Lutomirski 2017-04-10 20:17 ` Andy Lutomirski 2017-04-07 19:25 ` Thomas Gleixner 2017-04-07 19:25 ` Thomas Gleixner 2017-04-07 19:25 ` Thomas Gleixner 2017-04-07 14:45 ` Peter Zijlstra 2017-04-07 14:45 ` Peter Zijlstra 2017-04-07 14:45 ` Peter Zijlstra 2017-04-10 10:29 ` Mark Rutland 2017-04-10 10:29 ` Mark Rutland 2017-04-10 10:29 ` Mark Rutland 2017-04-07 19:52 ` PaX Team 2017-04-07 19:52 ` PaX Team 2017-04-07 19:52 ` PaX Team 2017-04-10 8:26 ` Thomas Gleixner 2017-04-10 8:26 ` Thomas Gleixner 2017-04-10 8:26 ` Thomas Gleixner 2017-04-10 19:55 ` PaX Team 2017-04-10 19:55 ` PaX Team 2017-04-10 19:55 ` PaX Team 2017-04-07 9:37 ` Peter Zijlstra 2017-04-07 9:37 ` [kernel-hardening] " Peter Zijlstra 2017-04-07 9:37 ` Peter Zijlstra 2017-03-29 18:15 ` [RFC v2][PATCH 05/11] ARM: mm: dump: Add domain to output Kees Cook 2017-03-29 18:15 ` [kernel-hardening] " Kees Cook 2017-03-29 18:15 ` Kees Cook 2017-03-29 18:15 ` [RFC v2][PATCH 06/11] ARM: domains: Extract common USER domain init Kees Cook 2017-03-29 18:15 ` [kernel-hardening] " Kees Cook 2017-03-29 18:15 ` Kees Cook 2017-03-29 18:15 ` [RFC v2][PATCH 07/11] ARM: mm: set DOMAIN_WR_RARE for rodata Kees Cook 2017-03-29 18:15 ` [kernel-hardening] " Kees Cook 2017-03-29 18:15 ` Kees Cook 2017-03-29 18:16 ` [RFC v2][PATCH 08/11] ARM: Implement __arch_rare_write_begin/end() Kees Cook 2017-03-29 18:16 ` [kernel-hardening] " Kees Cook 2017-03-29 18:16 ` Kees Cook 2017-04-07 9:36 ` Peter Zijlstra 2017-04-07 9:36 ` [kernel-hardening] " Peter Zijlstra 2017-04-07 9:36 ` Peter Zijlstra 2017-03-29 18:16 ` [RFC v2][PATCH 09/11] list: add rare_write() list helpers Kees Cook 2017-03-29 18:16 ` [kernel-hardening] " Kees Cook 2017-03-29 18:16 ` Kees Cook 2017-03-29 18:16 ` [RFC v2][PATCH 10/11] gcc-plugins: Add constify plugin Kees Cook 2017-03-29 18:16 ` [kernel-hardening] " Kees Cook 2017-03-29 18:16 ` Kees Cook 2017-03-29 18:16 ` [RFC v2][PATCH 11/11] cgroups: force all struct cftype const Kees Cook 2017-03-29 18:16 ` [kernel-hardening] " Kees Cook 2017-03-29 18:16 ` Kees Cook 2017-03-29 19:00 ` [RFC v2] Introduce rare_write() infrastructure Russell King - ARM Linux 2017-03-29 19:00 ` [kernel-hardening] " Russell King - ARM Linux 2017-03-29 19:00 ` Russell King - ARM Linux 2017-03-29 19:14 ` Kees Cook 2017-03-29 19:14 ` [kernel-hardening] " Kees Cook 2017-03-29 19:14 ` Kees Cook
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