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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5310B60F.30806@zytor.com>
Date:	Fri, 28 Feb 2014 08:15:11 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 02/28/2014 07:40 AM, Peter Zijlstra wrote:
> 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.
> 

Well, I was talking about the assumption spelled out in the comment
above copy_from_user_nmi() which pretty much states "cr2 is safe because
cr2 is saved/restored in the NMI wrappers."

	-hpa
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/