Cannot debug hypervisor

WINDBG
1

I'm using WinDbg to debug my hypervisor. But seems like reliance of interrupts causes issues. This has never happened before. When I put a breakpoint to anywhere in my host code, the WinDbg successfully hits the breakpoint. But after a few instructions of assembly, WinDbg freezes for 30 seconds. Saying "busy". And then, I'm welcomed with a page fault because stack is somehow trashed and my VmExit handler is triggered.

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The run_vmx_guest on the stack is where the guest register restoration happens. And due to its reliance on stack, and since stack is garbage, it page faults.

The problem doesn't happen when a breakpoint isn't put. It works perfectly fine even whee WinDbg is attached. Everything goes wrong after hitting a breakpoint.

I haven't tinkered with host IDT or something. It's same as the normal IDT. This issue didn't happen before. It just began.

2

Try this, do your development in an emulated QEMU virtual machine. Connect windbg to the QEMU gdb interface using the windbg exdi adapter (it works pretty well with qemu). I’ve done things like this on ARM64, but think this all works on x64 too. So then the windbg stub does not run on the target machine, it has run control and memory read/write thought the qemu gdb stub, so you can single step through interrupts or whatever. It’s not quite an nice as native windbg, but can debug situations that normal windbg can’t. I’m not sure windbg will be so happy when you change VMs, but with the exdi interface you could refresh the connection and get windbg to get it’s context synced for the new vm context.