Otherwise besides mis-handling the instruction, the comparison failure
case would result in uninitialized stack data being handed back to the
guest in rDX:rAX (32 bits leaked for 32-bit guests, 96 bits for 64-bit
ones).
This is CVE-2016-9932 / XSA-200.
Signed-off-by: Jan Beulich <jbeulich@suse.com>