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

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Message-ID: <20140228103005.0dbe31e1@gandalf.local.home>
Date:	Fri, 28 Feb 2014 10:30:05 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Seiji Aguchi <seiji.aguchi@....com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot

On Fri, 28 Feb 2014 10:20:00 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> Below is a patch that should fix this. Please remove all other patches
> and try this out.

Updated patch, as Peter Zijlstra on IRC asked me if the
exception_enter() can be traced. And looking at it, it sure can be.

-- Steve

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 6dea040..f606b67 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1271,9 +1271,15 @@ dotraplinkage void __kprobes
 trace_do_page_fault(struct pt_regs *regs, unsigned long error_code)
 {
 	enum ctx_state prev_state;
+	unsigned long cr2;
 
+	/* The trace might fault, save the cr2 register */
+	cr2 = read_cr2();
 	prev_state = exception_enter();
 	trace_page_fault_entries(regs, error_code);
+	/* Put back the original cr2 if needed */
+	if (cr2 != read_cr2())
+		write_cr2(cr2);
 	__do_page_fault(regs, error_code);
 	exception_exit(prev_state);
 }
--
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