Re: Sanitize CPU-state when switching from virtual-8086 mode to othertask

From: H. Peter Anvin
Date: Sun Dec 29 2013 - 20:19:54 EST

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?


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