From: "H. Peter Anvin" <hpa@zytor.com>
To: Vince Weaver <vincent.weaver@maine.edu>
Cc: Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot
Date: Tue, 25 Feb 2014 06:34:55 -0800 [thread overview]
Message-ID: <dde99a03-9f97-4cd9-aeef-cb0dcc62a7dc@email.android.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1402250904400.23234@vincent-weaver-1.um.maine.edu>
#2 is what I really don't understand.
I worry something else is going on there
On February 25, 2014 6:07:51 AM PST, Vince Weaver <vincent.weaver@maine.edu> wrote:
>On Mon, 24 Feb 2014, H. Peter Anvin wrote:
>
>> On 02/24/2014 11:30 AM, Peter Zijlstra wrote:
>> > On Mon, Feb 24, 2014 at 02:13:29PM -0500, Steven Rostedt wrote:
>> >> Ah, and x86_64 saves off the cr2 register when entering NMI and
>restores
>> >> it before returning. But it seems to be missing from the i386
>code.
>> >
>> > arch/x86/kernel/nmi.c:
>> >
>> > #define nmi_nesting_preprocess(regs) \
>> > do { \
>> > if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) { \
>> > this_cpu_write(nmi_state, NMI_LATCHED); \
>> > return; \
>> > } \
>> > this_cpu_write(nmi_state, NMI_EXECUTING); \
>> > this_cpu_write(nmi_cr2, read_cr2()); \
>> > } while (0); \
>> > nmi_restart:
>> >
>> > #define nmi_nesting_postprocess() \
>> > do { \
>> > if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) \
>> > write_cr2(this_cpu_read(nmi_cr2)); \
>> > if (this_cpu_dec_return(nmi_state)) \
>> > goto nmi_restart; \
>> > } while (0)
>> >
>> > That very much looks like saving/restoring CR2 to me.
>> >
>> > FWIW; I hate how the x86_64 and i386 versions of this NMI nesting
>magic
>> > are so completely different.
>>
>> Is there any way that nmi_cr2 can end up getting overwritten by
>multiple
>> nestings of some kind? I would have thought it would have made more
>> sense to spill cr2 onto the stack after the stack has been properly
>set up.
>
>So how can I help with debugging this?
>
>While the missing cr2 issue made debugging frustrating, I find the
>other
>aspects of the bug more serious:
>
> 1. Programs that are doing valid memory accesses can segfault
>and worse
>2. This bug can cause an instant-reboot of the system (I assume
>somehow
> with the right combination of memory accesses it causes a
> triple-fault?)
>
>#2 is why I spent all of this time tracking this down, I couldn't leave
>a
>machine fuzzing overnight without the machine rebooting.
>
>Vince
--
Sent from my mobile phone. Please pardon brevity and lack of formatting.
next prev parent reply other threads:[~2014-02-25 14:36 UTC|newest]
Thread overview: 115+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-21 20:25 perf_fuzzer causes reboot Vince Weaver
2014-02-21 22:13 ` perf_fuzzer compiled for x32 " Vince Weaver
2014-02-21 22:34 ` Vince Weaver
2014-02-22 4:50 ` Vince Weaver
2014-02-22 5:03 ` H. Peter Anvin
2014-02-22 6:26 ` H. Peter Anvin
2014-02-23 5:18 ` Vince Weaver
2014-02-23 5:24 ` H. Peter Anvin
2014-02-23 6:07 ` H. Peter Anvin
2014-02-23 14:05 ` Vince Weaver
2014-02-24 3:02 ` Vince Weaver
2014-02-24 5:22 ` H. Peter Anvin
2014-02-24 15:35 ` Vince Weaver
2014-02-24 16:34 ` Vince Weaver
2014-02-24 16:47 ` H. Peter Anvin
2014-02-24 17:10 ` Vince Weaver
2014-02-24 17:25 ` Peter Zijlstra
2014-02-24 17:32 ` Vince Weaver
2014-02-24 17:40 ` H. Peter Anvin
2014-02-24 18:00 ` Vince Weaver
2014-02-24 18:07 ` Vince Weaver
2014-02-24 18:34 ` H. Peter Anvin
2014-02-24 19:13 ` Steven Rostedt
2014-02-24 19:15 ` H. Peter Anvin
2014-02-24 19:30 ` Peter Zijlstra
2014-02-24 19:32 ` Steven Rostedt
2014-02-25 3:49 ` H. Peter Anvin
2014-02-25 14:07 ` Vince Weaver
2014-02-25 14:34 ` H. Peter Anvin [this message]
2014-02-25 14:43 ` Steven Rostedt
2014-02-25 15:33 ` Vince Weaver
2014-02-26 15:06 ` Vince Weaver
2014-02-27 22:06 ` Vince Weaver
2014-02-27 22:31 ` Steven Rostedt
2014-02-27 22:52 ` H. Peter Anvin
2014-02-27 23:30 ` Steven Rostedt
2014-02-27 23:46 ` H. Peter Anvin
2014-02-28 1:00 ` Vince Weaver
2014-02-28 20:34 ` Paul E. McKenney
2014-02-28 20:47 ` Steven Rostedt
2014-02-28 20:54 ` Peter Zijlstra
2014-02-28 21:17 ` Paul E. McKenney
2014-02-28 21:27 ` Peter Zijlstra
2014-02-28 21:51 ` Paul E. McKenney
2014-02-28 21:55 ` Peter Zijlstra
2014-02-28 22:05 ` Steven Rostedt
2014-02-28 22:23 ` Paul E. McKenney
2014-02-28 1:34 ` Vince Weaver
2014-02-28 2:17 ` H. Peter Anvin
2014-02-28 2:57 ` Steven Rostedt
2014-02-28 11:11 ` Peter Zijlstra
2014-02-28 13:37 ` Steven Rostedt
2014-02-28 14:15 ` Vince Weaver
2014-02-28 14:23 ` Steven Rostedt
2014-02-28 15:07 ` Vince Weaver
2014-02-28 15:13 ` H. Peter Anvin
2014-02-28 15:40 ` Peter Zijlstra
2014-02-28 16:15 ` H. Peter Anvin
2014-02-28 16:29 ` Steven Rostedt
2014-02-28 19:33 ` [PATCH] x86: Rename copy_from_user_nmi() to copy_from_user_trace() Steven Rostedt
2014-02-28 20:46 ` Peter Zijlstra
2014-02-28 20:51 ` Steven Rostedt
2014-02-28 20:58 ` Peter Zijlstra
2014-02-28 21:01 ` Steven Rostedt
2014-02-28 21:17 ` Peter Zijlstra
2014-02-28 20:56 ` perf_fuzzer compiled for x32 causes reboot Peter Zijlstra
2014-02-28 21:06 ` Steven Rostedt
2014-03-01 9:16 ` Ingo Molnar
2014-03-01 9:50 ` Borislav Petkov
2014-03-01 16:50 ` H. Peter Anvin
2014-03-04 23:05 ` Borislav Petkov
2014-03-03 9:16 ` Peter Zijlstra
2014-02-28 20:55 ` Peter Zijlstra
2014-02-28 15:20 ` Steven Rostedt
2014-02-28 15:30 ` Steven Rostedt
2014-02-28 20:38 ` H. Peter Anvin
2014-02-28 20:46 ` Steven Rostedt
2014-02-28 21:18 ` Vince Weaver
2014-02-28 21:30 ` Steven Rostedt
2014-02-28 23:34 ` Vince Weaver
2014-03-01 0:43 ` H. Peter Anvin
2014-03-01 3:36 ` Steven Rostedt
2014-03-01 16:24 ` Andi Kleen
2014-03-02 15:34 ` Vince Weaver
2014-03-02 16:02 ` Vince Weaver
2014-02-28 9:39 ` Peter Zijlstra
2014-02-24 17:40 ` Peter Zijlstra
2014-02-24 17:41 ` Vince Weaver
2014-02-24 17:42 ` H. Peter Anvin
2014-02-24 17:52 ` H. Peter Anvin
2014-02-28 15:33 [PATCH] x86 trace: Fix page fault tracing bug Jiri Olsa
2014-02-28 15:47 ` Peter Zijlstra
2014-02-28 16:05 ` [PATCHv2] " Jiri Olsa
2014-02-28 16:11 ` H. Peter Anvin
2014-02-28 16:23 ` Steven Rostedt
2014-02-28 16:15 ` Steven Rostedt
2014-03-05 0:03 ` [tip:x86/urgent] x86, trace: Fix CR2 corruption when tracing page faults tip-bot for Jiri Olsa
2014-03-05 11:14 ` Peter Zijlstra
2014-03-05 12:20 ` Steven Rostedt
2014-03-05 12:25 ` Peter Zijlstra
2014-03-05 12:33 ` Steven Rostedt
2014-03-05 12:54 ` Peter Zijlstra
2014-03-05 13:02 ` Peter Zijlstra
2014-03-05 13:07 ` Peter Zijlstra
2014-03-05 12:36 ` Peter Zijlstra
2014-03-05 13:00 ` Steven Rostedt
2014-03-05 13:08 ` Peter Zijlstra
2014-03-05 21:37 ` H. Peter Anvin
2014-03-06 8:40 ` Peter Zijlstra
2014-03-06 11:02 ` Steven Rostedt
2014-03-06 14:53 ` [PATCH] x86: Further robustify CR2 handling vs tracing Peter Zijlstra
2014-03-07 23:07 ` [tip:x86/urgent] x86, trace: " tip-bot for Peter Zijlstra
2014-02-28 15:47 ` [PATCH] x86 trace: Fix page fault tracing bug Jiri Olsa
2014-02-28 16:00 ` Steven Rostedt
2014-02-28 16:01 ` Steven Rostedt
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