linux-kernel - Re: Sanitize CPU-state when switching from virtual-8086 mode to other task

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Message-ID: <52C0C9F4.50101@zytor.com>
Date:	Sun, 29 Dec 2013 17:18:44 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	halfdog <me@...fdog.net>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
CC:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: Sanitize CPU-state when switching from virtual-8086 mode to other
 task

On 12/29/2013 12:44 PM, halfdog wrote:
> H. Peter Anvin wrote:
>> On 12/28/2013 02:02 PM, halfdog wrote:
>>> It seems that missing CPU-state sanitation during task 
>>> switching triggers kernel-panic. This might be related to 
>>> unhandled FPU-errors. See [1] for POC and serial console log
>>> of OOPs. Due to missing real 32-bit x86-hardware it is not
>>> clear, if this issue might be related to subtle differences in 
>>> virtual-8086 mode handling when inside a virtualbox guest.
>>> 
> 
>> This oops happens inside the guest?  Either way, I would be 
>> *very* skeptical of Virtualbox in this case.
> 
>> You can run a 32-bit kernel on 64-bit hardware, you know...
> 
> I know, but hardware was occupied with long-running simulation.
> 
> With the initial POC, there might be a timing issue involved, with
>  different process layout, exception does not occur in swith_to but
>  sometimes on other locations.
> 
> I created a new random-code testcase [1] , which works around that
>  problem. When booted a Debian initrd and tried id, OOPSes are 
> fired like wild but at least system does not lock up immediately.
> 

Still in VirtualBox?

	-hpa


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