s390/zcrypt: Pad trailing CCA or EP11 message with zeros

In the Linux kernel, the following vulnerability has been resolved:

s390/zcrypt: Pad trailing CCA or EP11 message with zeros

The both functions xcrb_msg_to_type6cprb_msgx() and xcrb_msg_to_type6_ep11cprb_msgx() copy the user space message into a kernel buffer based on the message length. But on further processing the message is supposed to be 4 byte length adjusted. Thus up to 3 bytes of uninitialized kernel memory are forwarded to further processing steps and may unwanted expose kernel memory to the crypto card firmware.

This patch contains code to pad the gap between user space copied message and message buffer length sent down to further processing of the CCA or EP11 message to zeros.