information leak via internal x86 system device emulation
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.
uninitialized memory, hypervisor栈上的内容会被拷贝到虚拟机。
x86/HVM: return all ones on wrong-sized reads of system device I/O ports
So far the value presented to the guest remained uninitialized.
*val = ~0;
A malicious HVM guest might be able to read sensitive data relating to other guests.