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

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Message-ID: <20140224141329.1cd3bb52@gandalf.local.home>
Date:	Mon, 24 Feb 2014 14:13:29 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>, "H.J. Lu" <hjl.tools@...il.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot

On Mon, 24 Feb 2014 10:34:13 -0800
"H. Peter Anvin" <hpa@...or.com> wrote:

> On 02/24/2014 10:07 AM, Vince Weaver wrote:
> >>
> >> Anyway I've attached the full tail end of the trace if you want to see 
> >> everything that happens.
> > 
> > and then I note there are *two* kernel page faults.
> > 
> >      perf_fuzzer-2979  [000]   161.475924: page_fault_kernel:    address=irq_stack_union ip=copy_user_generic_string error_code=0x0
> > address=0x1 ip=0xffffffff812a7d9c error_code=0x0
> >      perf_fuzzer-2979  [000]   161.475924: function:                __do_page_fault
> >      perf_fuzzer-2979  [000]   161.475924: function:                   bad_area_nosemaphore
> >      perf_fuzzer-2979  [000]   161.475925: function:                      __bad_area_nosemaphore
> >      perf_fuzzer-2979  [000]   161.475925: function:                         no_context
> >      perf_fuzzer-2979  [000]   161.475925: function:                            fixup_exception
> >      perf_fuzzer-2979  [000]   161.475926: function:                               search_exception_tables
> >      perf_fuzzer-2979  [000]   161.475926: function:                                  search_extable
> >      perf_fuzzer-2979  [000]   161.475927: function:             copy_user_handle_tail
> >      perf_fuzzer-2979  [000]   161.475927: function:             trace_do_page_fault
> >      perf_fuzzer-2979  [000]   161.475928: page_fault_kernel:    address=irq_stack_union ip=copy_user_handle_tail error_code=0x0
> > address=0x1 ip=0xffffffff812a92bb error_code=0x0
> >      perf_fuzzer-2979  [000]   161.475928: function:                __do_page_fault
> >      perf_fuzzer-2979  [000]   161.475928: function:                   bad_area_nosemaphore
> >      perf_fuzzer-2979  [000]   161.475929: function:                      __bad_area_nosemaphore
> >      perf_fuzzer-2979  [000]   161.475929: function:                         no_context
> >      perf_fuzzer-2979  [000]   161.475929: function:                            fixup_exception
> >      perf_fuzzer-2979  [000]   161.475929: function:                               search_exception_tables
> >      perf_fuzzer-2979  [000]   161.475930: function:                                  search_extable
> >      perf_fuzzer-2979  [000]   161.475931: function:             perf_output_begin
> >      perf_fuzzer-2979  [000]   161.475931: function:             perf_output_copy
> > 
> > That second one is in copy_user_handle_tail()
> > 
> 
> Either way, it really seems like we have a case of CR2 leakage out of
> the NMI context.

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.

-- Steve
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