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Date: Fri, 28 Feb 2014 09:23:41 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: Vince Weaver <vincent.weaver@maine.edu>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Peter Zijlstra <peterz@infradead.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot
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On Fri, 28 Feb 2014 09:15:33 -0500 (EST)
Vince Weaver <vincent.weaver@maine.edu> wrote:

> On Thu, 27 Feb 2014, Steven Rostedt wrote:
> 
> > On Thu, 27 Feb 2014 20:34:34 -0500 (EST)
> > Vince Weaver <vincent.weaver@maine.edu> wrote:
> > 
> > 
> > > > 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.
> > > 
> > 
> > Vince, Great! Can you remove Peter's patch, and try this one. It
> > removes the crud to save the cr2 from entry_64.S and makes both i386
> > and x86_64 do the same thing in regards to cr2 handling.
> 
> no, with only this patch applied it segfaults as per previous:
> 
> [  126.396049] perf_fuzzer[2904]: segfault at 17a0 ip 00000000004017fd sp 00000000ffaff3f0 error 6 in perf_fuzzer[400000+d1000]

Interesting. Are you doing a perf function trace?

And just in case, can you add this patch and make sure the copy is
called by NMI.

-- Steve

diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index ddf9ecb..ca943cd 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -29,6 +29,7 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
 	 */
 	pagefault_disable();
 	ret = __copy_from_user_inatomic(to, from, n);
+	trace_dump_stack(2)
 	pagefault_enable();
 
 	return ret;