Xen through 4.14.x allows guest OS administrators to obtain sensitive information (such as AES keys from outside the guest) via a side-channel attack on a power/energy monitoring interface, aka a "Platypus" attack. NOTE: there is only one logically independent fix: to change the access control for each such interface in Xen.
https://xenbits.xen.org/xsa/advisory-351.html
https://www.zdnet.com/article/new-platypus-attack-can-steal-data-from-intel-cpus/
https://www.debian.org/security/2020/dsa-4804