Re: [GSoC] GSoC Introduction : Fuzzing Xen hypercall interface

[Wei Liu <wei.liu2@citrix.com>]

On Thu, Mar 16, 2017 at 04:53:38PM +0100, Felix Schmoll wrote:
[...]
> 
> Hi,
> 
> I installed Xen from source and I figured out that for the hypercall I have
> to make a two-line change in xen/xen/common/kernel.c and a couple of
> headers. I mostly went with what I got by grepping for the
> "xen_version"-hypercall. It seems really basic but after struggling with
> this for quite a while I have some questions:
> 
> 1.
> -How do I test this? The usual way to make hypercalls seems to use the
> libxc-library, so do I have to change that as well?

Good question. You can do it in the libxc library. You write a function
for libxc, which then calls into the libxencall library to issue the
hypercall. There are plenty of examples there.

> -The "xen_version"-hypercall had a couple of COMPAT_versions, do I need
> them? This seems to be related with if I need to support both ARM and x86,
> although I'm really not sure here. Is it fine to just choose to support the
> one which my hypervisor is running on?

The compat layer is to support 32 bit guests on 64 bit Xen. You can
ignore that for this simple exercise, just run 64 bit guests on 64 bit
hypervisor.


> -Do I need to make changes in the XSM module? Again, this pops up when
> grepping for xen_version but it's disabled by default anyways and I'd
> otherwise just try to have a minimal working set.

Ignore that for now.

> 
> 2.
> -A stub for what? dom0?
> 

You will need to provide a function in order to use the trace-pc
mechanism. For now just provide an empty stub function is fine.

When it comes to the real project, the function will be filled in.

Again, feel free to ask more questions.

Wei.

> Felix

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