The make_response function in drivers/block/xen-blkback/blkback.c in the Linux kernel before 4.11.8 allows guest OS users to obtain sensitive information from host OS (or other guest OS) kernel memory by leveraging the copying of uninitialized padding fields in Xen block-interface response structures, aka XSA-216.
https://github.com/torvalds/linux/commit/089bc0143f489bd3a4578bdff5f4ca68fb26f341
https://lists.debian.org/debian-lts-announce/2018/09/msg00007.html
https://security.gentoo.org/glsa/201708-03
https://xenbits.xen.org/xsa/advisory-216.html
http://www.debian.org/security/2017/dsa-3920
http://www.debian.org/security/2017/dsa-3927
http://www.debian.org/security/2017/dsa-3945
http://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.11.8