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

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Message-ID: <20140228154026.GH9987@twins.programming.kicks-ass.net>
Date:	Fri, 28 Feb 2014 16:40:26 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot

On Fri, Feb 28, 2014 at 07:13:06AM -0800, H. Peter Anvin wrote:
> If I'm reading this right we end up going from the page fault
> tracepoint to copy_from_user_nmi() without going through NMI, and the
> cr2 corruption is obvious.  I guess the assumption that only the NMI
> path needed to save cr2 is flawed?

It was never assumed it would only go through NMI, but that it would be
NMI safe -- and as it turns out, it is that.

What I did assume was that any other callsites would be safe, seeing how
they'd already be running in 'normal' contexts.

I had not considered people putting tracepoints _that_ early in the
exception paths.

Note that there's more tracepoints there than the one mentioned.
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