Re: [Xen-devel] VMI: singlestep event not received

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Mon, Apr 22, 2019 at 6:00 PM Mathieu Tarral
<mathieu.tarral@xxxxxxxxxxxxxx> wrote:
>
> On Monday 22 April 2019 11:22, Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx> 
> wrote:
>
> > On 4/22/19 1:26 AM, Mathieu Tarral wrote:
> >
> > > The problem is that RtlUserThreadStart is paged-out, so i'm trying to 
> > > reach it via singlestepping as a backup solution.
> >
> > FWIW, you can just use xc_hvm_inject_trap() with a TRAP_page_fault
> > parameter to cause the OS to bring a paged out page back into main memory.
>
> The problem is that i'm fully based on LibVMI, which doesn't provide an API 
> for page injection yet.
>
> I think Tamas was waiting for a full support of pagefault injection on Xen 
> before opening an API.
>
> Maybe we should open an issue to track the progress about it.
>
> Thanks anyway for the suggestion !

Not having a LibVMI wrapper should not prevent you from using a libxc
function directly. There are many corner-cases regarding when it is
safe to inject a pagefault into the guest to bring back pages and that
logic is not trivial enough to be implemented in LibVMI. It's way too
specific to the usecase to decide when it's safe to do that. So in
this case, if you know you are in ring3 of your target process you can
just call the libxc function directly.

Tamas

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