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).
Regards,
Sander
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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