From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: Elena Reshetova <elena.reshetova@intel.com>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>,
Arnd Bergmann <arnd@arndb.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
"H. Peter Anvin" <h.peter.anvin@intel.com>,
Will Deacon <will.deacon@arm.com>,
Hans Liljestrand <ishkamiel@gmail.com>,
David Windsor <dwindsor@gmail.com>
Subject: [kernel-hardening] Re: [RFC v4 PATCH 12/13] x86: implementation for HARDENED_ATOMIC
Date: Fri, 11 Nov 2016 21:19:43 +0100 [thread overview]
Message-ID: <20161111201943.GR3117@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CAGXu5j++ZZDmgYqzvx104Bs2iQK+7V_Xn2VgTR7eoCwS2JR0tw@mail.gmail.com>
On Fri, Nov 11, 2016 at 10:00:27AM -0800, Kees Cook wrote:
> Agreed: the first thread will BUG and the second thread is still halfway to 0.
>
> On systems that panic on BUG, things are protected. For the rest of
> the systems, an alternative to "dec" on overflow is to sub (more than)
> NR_CPUS, to keep the saturation below the overflow level. This means
> that it is still detected (BUG) by at least 1 thread, and cannot reach
> 0 (to trigger the flaw) on all other threads, even if they all lose
> the race.
NR_CPUS has nothing to do with anything here. If this is a vcpu that got
scheduled out in between the inc and dec there can be an arbitrary
amount of other crap happening.
> To me, this seems better than taking the cmpxchg performance hit.
To me that shows you shouldn't be allowed near atomic_t. You cannot have
a non-atomic atomic op. That just doesn't happen.
next prev parent reply other threads:[~2016-11-11 20:19 UTC|newest]
Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-10 20:24 [kernel-hardening] [RFC v4 PATCH 00/13] HARDENED_ATOMIC Elena Reshetova
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 01/13] Add architecture independent hardened atomic base Elena Reshetova
2016-11-10 20:41 ` [kernel-hardening] " David Windsor
2016-11-10 21:09 ` Peter Zijlstra
2016-11-10 21:35 ` Peter Zijlstra
2016-11-11 9:06 ` Reshetova, Elena
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 02/13] percpu-refcount: leave atomic counter unprotected Elena Reshetova
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 03/13] kernel: identify wrapping atomic usage Elena Reshetova
2016-11-10 21:58 ` [kernel-hardening] " Peter Zijlstra
2016-11-11 8:49 ` [kernel-hardening] " Reshetova, Elena
2016-11-19 13:28 ` [kernel-hardening] " Paul E. McKenney
2016-11-19 21:39 ` Kees Cook
2016-11-21 20:13 ` Paul E. McKenney
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 04/13] mm: " Elena Reshetova
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 05/13] fs: " Elena Reshetova
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 06/13] net: " Elena Reshetova
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 07/13] net: atm: " Elena Reshetova
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 08/13] security: " Elena Reshetova
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 09/13] drivers: identify wrapping atomic usage (part 1/2) Elena Reshetova
2016-11-10 21:48 ` [kernel-hardening] " Will Deacon
2016-11-11 8:57 ` [kernel-hardening] " Reshetova, Elena
2016-11-11 12:35 ` Mark Rutland
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 10/13] drivers: identify wrapping atomic usage (part 2/2) Elena Reshetova
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 11/13] x86: identify wrapping atomic usage Elena Reshetova
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 12/13] x86: implementation for HARDENED_ATOMIC Elena Reshetova
2016-11-10 20:40 ` [kernel-hardening] " Peter Zijlstra
2016-11-10 21:04 ` Kees Cook
2016-11-10 21:16 ` Peter Zijlstra
2016-11-10 21:32 ` Kees Cook
2016-11-10 21:46 ` Peter Zijlstra
2016-11-10 22:50 ` Peter Zijlstra
2016-11-10 23:07 ` Kees Cook
2016-11-10 23:30 ` Peter Zijlstra
2016-11-11 9:32 ` [kernel-hardening] " Reshetova, Elena
2016-11-11 10:29 ` [kernel-hardening] " Peter Zijlstra
2016-11-11 18:00 ` Kees Cook
2016-11-11 20:19 ` Peter Zijlstra [this message]
2016-11-10 21:33 ` Peter Zijlstra
2016-11-11 9:20 ` [kernel-hardening] " Reshetova, Elena
2016-11-10 20:24 ` [kernel-hardening] [RFC v4 PATCH 13/13] lkdtm: add tests for atomic over-/underflow Elena Reshetova
2016-11-10 20:37 ` [RFC v4 PATCH 00/13] HARDENED_ATOMIC Peter Zijlstra
2016-11-10 20:37 ` [kernel-hardening] " Peter Zijlstra
2016-11-10 20:48 ` Will Deacon
2016-11-10 20:48 ` [kernel-hardening] " Will Deacon
2016-11-10 21:01 ` Kees Cook
2016-11-10 21:01 ` [kernel-hardening] " Kees Cook
2016-11-10 21:23 ` David Windsor
2016-11-10 21:27 ` Kees Cook
2016-11-10 21:27 ` Kees Cook
2016-11-10 21:39 ` David Windsor
2016-11-10 21:39 ` David Windsor
2016-11-10 21:39 ` Peter Zijlstra
2016-11-10 21:13 ` Peter Zijlstra
2016-11-10 21:13 ` [kernel-hardening] " Peter Zijlstra
2016-11-10 21:23 ` Kees Cook
2016-11-10 21:23 ` [kernel-hardening] " Kees Cook
2016-11-11 4:25 ` Rik van Riel
2016-11-10 22:27 ` Greg KH
2016-11-10 23:15 ` Kees Cook
2016-11-10 23:15 ` Kees Cook
2016-11-10 23:38 ` Greg KH
2016-11-10 23:38 ` Greg KH
2016-11-11 7:50 ` David Windsor
2016-11-11 17:43 ` Kees Cook
2016-11-11 17:46 ` Peter Zijlstra
2016-11-11 18:04 ` Kees Cook
2016-11-11 20:17 ` Peter Zijlstra
2016-11-14 20:31 ` Kees Cook
2016-11-15 8:01 ` Peter Zijlstra
2016-11-15 16:50 ` Rik van Riel
2016-11-15 17:23 ` Kees Cook
2016-11-16 17:09 ` Rik van Riel
2016-11-16 17:32 ` Peter Zijlstra
2016-11-16 17:41 ` Rik van Riel
2016-11-16 17:34 ` Reshetova, Elena
2016-11-17 8:37 ` Peter Zijlstra
2016-11-17 9:04 ` Reshetova, Elena
2016-11-17 9:36 ` Peter Zijlstra
2016-11-17 9:36 ` Julia Lawall
2016-11-17 10:16 ` Peter Zijlstra
2016-11-17 11:19 ` Mark Rutland
2016-11-17 11:32 ` Julia Lawall
2016-11-17 12:59 ` Julia Lawall
2016-11-11 18:47 ` Mark Rutland
2016-11-11 19:39 ` Will Deacon
2016-11-11 18:31 ` Mark Rutland
2016-11-11 20:05 ` Peter Zijlstra
2016-11-15 10:36 ` Mark Rutland
2016-11-15 11:21 ` Peter Zijlstra
2016-11-15 18:02 ` Mark Rutland
2016-11-10 23:57 ` Peter Zijlstra
2016-11-10 23:57 ` Peter Zijlstra
2016-11-11 0:29 ` Colin Vidal
2016-11-11 12:41 ` Mark Rutland
2016-11-11 12:47 ` Peter Zijlstra
2016-11-11 13:00 ` Peter Zijlstra
2016-11-11 14:39 ` Thomas Gleixner
2016-11-11 14:48 ` Peter Zijlstra
2016-11-11 23:07 ` Peter Zijlstra
2016-11-13 11:03 ` Greg KH
2016-11-13 11:03 ` Greg KH
2016-11-10 20:56 ` Kees Cook
2016-11-10 20:56 ` [kernel-hardening] " Kees Cook
2016-11-11 3:20 ` David Windsor
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