Re: Emulating in response of an int3 vm_event

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 01/12/15 01:21, Tamas K Lengyel wrote:
>
>
> On Mon, Nov 30, 2015 at 7:01 PM, Razvan Cojocaru
> <rcojocaru@bitdefender.com <mailto:rcojocaru@bitdefender.com>> wrote:
>
>     On 12/01/2015 01:32 AM, Tamas K Lengyel wrote:
>     > Hi all,
>     > I'm trying to extend the current vm_event system to be able to
>     emulate
>     > over an in-guest breakpoint using the
>     VM_EVENT_FLAG_SET_EMUL_READ_DATA
>     > feature. The idea is to have the vm_event listener send back the
>     > contents of the memory that was overwritten by the breakpoint
>     > instruction, have Xen emulate one instruction, and resume execution
>     > normally afterwards. This would eliminate the need of removing the
>     > breakpoint, singlestepping, and placing the breakpoint back again.
>     >
>     > Unfortunately I encounter this crash when I call
>     > hvm_mem_access_emulate_one in the event response handler:
>     >
>     > (XEN) vm_event.c:72:d0v0 Checking flags on int3 response 37
>     > (XEN) Xen BUG at /share/src/xen/xen/include/asm/hvm/vmx/vmx.h:372
>

This BUG() is the cause of the crash.

It is a bad parameter to VMREAD, by the looks of it.

~Andrew

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