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

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Date:	Thu, 27 Feb 2014 18:17:59 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vince Weaver <vincent.weaver@...ne.edu>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot

Ok... I think we're definitely talking about a cr2 leak.  The reboot might be a race condition in the NMI nesting handling maybe?

On February 27, 2014 5:34:34 PM PST, Vince Weaver <vincent.weaver@...ne.edu> wrote:
>On Thu, 27 Feb 2014, H. Peter Anvin wrote:
>
>> On 02/27/2014 02:31 PM, Steven Rostedt wrote:
>> > 
>> > Yeah, something is getting mesed up.
>> > 
>> 
>> What it *looks* like to me is that we try to nest the cr2
>save/restore,
>> which doesn't nest because it is a percpu variable.
>> 
>> ... except in the x86-64 case, we *ALSO* save/restore cr2 inside
>> entry_64.S, which makes the stuff in do_nmi completely redundant and
>> there for no good reason.
>> 
>> I would actually suggest we do the equivalent on i386 as well.
>> 
>> Vince, could you try this patch as an experiment?
>
>OK with your patch applied it does not segfault.
>
>The trace looks like you'd expect too:
>
>perf_fuzzer-2910  [000]   255.355331: page_fault_kernel:   
>address=irq_stack_union ip=copy_user_handle_tail error_code=0x0
>perf_fuzzer-2910  [000]   255.355331: function:               
>__do_page_fault
>perf_fuzzer-2910  [000]   255.355331: function:                  
>bad_area_nosemaphore
>perf_fuzzer-2910  [000]   255.355331: function:                     
>__bad_area_nosemaphore
>perf_fuzzer-2910  [000]   255.355332: function:                        
>no_context
>perf_fuzzer-2910  [000]   255.355332: function:                        
>   fixup_exception
>perf_fuzzer-2910  [000]   255.355332: function:                        
>      search_exception_tables
>perf_fuzzer-2910  [000]   255.355332: function:                        
>         search_extable
>perf_fuzzer-2910  [000]   255.355333: function:            
>perf_output_begin
>perf_fuzzer-2910  [000]   255.355333: bprint:              
>perf_output_begin: VMW: event type 2 config 2a st: 2c3e7
>perf_fuzzer-2910  [000]   255.355333: bprint:              
>perf_output_begin: VMW: before event->parent (nil)
>perf_fuzzer-2910  [000]   255.355334: bprint:              
>perf_output_begin: VMW: before rcu_dereference (nil)
>perf_fuzzer-2910  [000]   255.355334: function:            
>__do_page_fault
>perf_fuzzer-2910  [000]   255.355334: function:               
>down_read_trylock
>perf_fuzzer-2910  [000]   255.355334: function:               
>_cond_resched
>perf_fuzzer-2910  [000]   255.355335: function:                find_vma
>perf_fuzzer-2910  [000]   255.355335: function:               
>handle_mm_fault
>perf_fuzzer-2910  [000]   255.355335: function:                  
>__do_fault
>perf_fuzzer-2910  [000]   255.355335: bputs:               
>perf_mmap_fault: VMW: perf_mmap_fault
>perf_fuzzer-2910  [000]   255.355336: bprint:              
>perf_mmap_fault: VMW: perf_mmap_fault 0xffff8800cba6a980
>perf_fuzzer-2910  [000]   255.355336: function:            
>perf_mmap_to_page
>perf_fuzzer-2910  [000]   255.355336: function:            
>_cond_resched
>perf_fuzzer-2910  [000]   255.355336: function:                     
>unlock_page
>perf_fuzzer-2910  [000]   255.355336: function:                        
>page_waitqueue
>perf_fuzzer-2910  [000]   255.355337: function:                        
>__wake_up_bit
>perf_fuzzer-2910  [000]   255.355337: bputs:               
>perf_mmap_fault: VMW: perf_mmap_fault
>perf_fuzzer-2910  [000]   255.355337: function:            
>_cond_resched
>perf_fuzzer-2910  [000]   255.355337: function:                     
>_raw_spin_lock
>perf_fuzzer-2910  [000]   255.355337: function:                     
>page_add_file_rmap
>perf_fuzzer-2910  [000]   255.355338: function:                        
>__inc_zone_page_state
>perf_fuzzer-2910  [000]   255.355338: function:                        
>   __inc_zone_state
>perf_fuzzer-2910  [000]   255.355338: function:                     
>set_page_dirty
>perf_fuzzer-2910  [000]   255.355338: function:                        
>page_mapping
>perf_fuzzer-2910  [000]   255.355338: function:                        
>anon_set_page_dirty
>perf_fuzzer-2910  [000]   255.355339: function:                     
>unlock_page
>
>
>Vince

-- 
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