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

KVM: s390: Fix memory corruption by not reinjecting CK machine checks

Channel-subsystem damage machine checks are for the host channel
subsystem. The guest channel subsystem is emulated in the userspace VMM.
There is no point in forwarding such machine checks into the guest.

This also simplifies the machine check reinjection and avoids kfree of a
stack variable as reported by sashiko.  There might be still machine
checks that have the ck bit set with another bit (like instruction
damage), mask out the CK bit in s390_backup_mcck_info(), like the CP and
ED bits already are.