Re: CVE request: kernel: KVM: x86: Disallow hypercalls for guest callers in rings > 0

[Eugene Teo <eugene () redhat com>]

Eugene Teo wrote:
> "So far unprivileged guest callers running in ring 3 can issue, e.g., 
> MMU hypercalls. Normally, such callers cannot provide any hand-crafted 
> MMU command structure as it has to be passed by its physical address, 
> but they can still crash the guest kernel by passing random addresses.
>
> To close the hole, this patch considers hypercalls valid only if issued 
> from guest ring 0. This may still be relaxed on a per-hypercall base in 
> the future once required."

So, besides the crash, users in the guest can access the guest kernel 
memory, so the impact is actually more serious than what was noted in 
the commit changelog. Take note.

Eugene