linux-kernel - Re: perf_fuzzer compiled for x32 causes reboot

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Date:	Sat, 22 Feb 2014 21:24:11 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vince Weaver <vincent.weaver@...ne.edu>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, "H.J. Lu" <hjl.tools@...il.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot

What is the instructions around it, by any chance?

On February 22, 2014 9:18:17 PM PST, Vince Weaver <vincent.weaver@...ne.edu> wrote:
>On Fri, 21 Feb 2014, H. Peter Anvin wrote:
>
>> Error 6 reflects a write in userspace to a not-present page.
>> 
>> Since your previous trace indicates that the value of the register in
>question
>> is a different one, I'm guessing that what we have here is PEBS
>getting
>> activated.  0x120 is 2*0x90, and 0x90 is the size of a 64-bit PEBS
>record.
>
>I'm having problems generating a replayable syscall trace that exhibits
>
>the problem.
>
>It turns out that the segfault address listed (the multiple of 0x120) 
>happens to be the value in the RBP register at the time of the
>segfault.
>
>That's odd, as the instruction is
>	movdqa %xmm0,(%rdi)
>and rdi is the valid mmap address of the perf ring buffer
>	rdi            0xf7768000	4151738368
>
>so I'm not sure why RBP is involved at all.
>
>In all of the cases I've investigated the precise_ip value has been set
>
>for the problem event... but none of the events have been hardware
>events
>(software and breakpoint so far).  So probably not PEBS related?
>
>Vince

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