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

[Eugene Teo <eugeneteo () kernel sg>]

"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."

This was introduced in v2.6.25-rc1, and fixed in 2.6.31.

cvss2=7.2/AV:L/AC:L/Au:N/C:C/I:C/A:C

Upstream commit:
http://git.kernel.org/linus/07708c4af1346ab1521b26a202f438366b7bcffd

References:
http://patchwork.kernel.org/patch/38926/
https://bugzilla.redhat.com/show_bug.cgi?id=524124

Thanks, Eugene