Re: KVM hook for code integrity checking

[Avi Kivity <avi@redhat.com>]

On 04/30/2010 05:53 PM, Suen Chun Hui wrote:
> Dear KVM developers,
>
> I'm currently working on an open source security patch to use KVM to
> implement code verification on a guest VM in runtime. Thus, it would be
> very helpful if someone can point to me the right function or place to
> look at for adding 2 hooks into the KVM paging code to:
>
> 1. Detect a new guest page (which I assume will imply a new pte and
> imply a new spte).
> Currently, I'm considering putting a hook in the function
> mmu_set_spte(), but may there is a better place.
> This hook will be used as the main entry point into the code
> verification function
>    

This is in general not possible.  Hosts with npt or ept will not see new 
guest ptes.

It could be done with physical pages, but you'll have no way of knowing 
if the pages are used in userspace, the kernel, or both.

> 2. Detect a write fault to a read-only spte (eg. for the case of
> updating the dirty bit back to the guest pte)
> Unfortunately, I'm unable to find an appropriate place where this
> actually takes place after reading the code many times.
> This hook will be used to prevent a secondary "peek" page from modifying
> an existing verified code page.
>    

set_spte() or mmu_set_spte() may work.

-- 
error compiling committee.c: too many arguments to function