xen-kernel -- Information leak via internal x86 system device emulation

The Xen Project reports:

Emulation routines in the hypervisor dealing with certain system devices check whether the access size by the guest is a supported one. When the access size is unsupported these routines failed to set the data to be returned to the guest for read accesses, so that hypervisor stack contents are copied into the destination of the operation, thus becoming visible to the guest.

A malicious HVM guest might be able to read sensitive data relating to other guests.

[source]