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

From: halfdog
Date: Sun Dec 29 2013 - 15:47:01 EST

Hash: SHA1

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.



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