[vbox-dev] IDT kernel patching

Sander van Leeuwen Sander.Vanleeuwen at Sun.COM
Wed Oct 8 11:14:59 GMT 2008

Do you execute sidt and patch the IDT with interrupts turned off? (IF=0)
Sidt is a non-faulting supervisor instruction that will give you our 
shadow tables if it's not patched. If you clear IF,
then you will get the right guest table pointer.

This limitation does not apply to hardware virtualization (VT-x & AMD-V).



albert wrote:
> Greetings all,
> My apologies if this is not the correct newsgroup for the following 
> question:
> I am patiently migrating the rr0d kernel debugger 
> (http://rr0d.droids-corp.org/)
> to run smoothly inside a windows xp guest. The host system is a Debian 
> running virtualbox 1.6.2. <http://1.6.2.>
> Video direct memory access seems to be partially fine, but the biggest 
> problem seems to be the interrupt table patching.
> It would appear that Virtualbox doesn't like anybody from touching the 
> kernel supervisor arena,
> even from ring 0. Is this a limitation of the software? Or is the 
> debugger really doing something nasty?
> The debugger code calls the mnemonic sidt to obain the base address to 
> the IDT (which works fine) and then patches several entries to get 
> control over certain interrupts (int 0, 3, 13 and a few others)
> During this operation, I get the following entries in the virtualbox 
> log file:
>              FATAL ERROR: trpmgcShadowIDTWriteHandler: eip=F4226AD2 
> pvFault=F700F468 pvRange=F700F450
>              CheckPageFault: write to hypervisor region f700f46c
>              FATAL ERROR: trpmgcShadowIDTWriteHandler: eip=F4226AF3 
> pvFault=F700F46C pvRange=F700F450
> Any suggestions greatly appreciated.
> cheers,
> albert
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Kind regards / Mit freundlichen Gruessen / Met vriendelijke groet


Sun Microsystems GmbH        Sander van Leeuwen
Werkstrasse 24               Senior Staff Engineer, VirtualBox
71384 Weinstadt, Germany     mailto:Sander.Vanleeuwen at sun.com

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