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

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Message-ID: <530B86CB.3070702@zytor.com>
Date:	Mon, 24 Feb 2014 09:52:11 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Vince Weaver <vincent.weaver@...ne.edu>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H.J. Lu" <hjl.tools@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: perf_fuzzer compiled for x32 causes reboot

On 02/24/2014 09:25 AM, Peter Zijlstra wrote:
>>
>> What is likely happening is the user page fault is triggering 
>> code to do a "perf_callchain" dump, which is calling copy_from_user_nmi()
>> which calls copy_user_generic_string() which is somehow getting the user
>> RBP in the RDI register somehow?
> 
> So that code very much relies on the 'recursive' NMI/iret magic from
> Steve, patch 3f3c8b8c4b2a3 (and assorted fixes later).
> 
> If CR2 is getting corrupted; 7fbb98c5cb075 seems relevant.
> 
> Peter, does x32 have a slightly different ABI/calling convention that
> would make any of these patches just slightly 'off'?
> 

As long as we're talking kernel code, x32 isn't even involved (we do not
support compiling the kernel as x32 and most likely never will.)

	-hpa


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