The xen_biovec_phys_mergeable function in drivers/xen/biomerge.c in Xen might allow local OS guest users to corrupt block device data streams and consequently obtain sensitive memory information, cause a denial of service, or gain host OS privileges by leveraging incorrect block IO merge-ability calculation.
https://usn.ubuntu.com/3655-2/
https://usn.ubuntu.com/3655-1/
https://support.citrix.com/article/CTX225941
https://security.gentoo.org/glsa/201801-14
https://bugzilla.redhat.com/show_bug.cgi?id=1477656
http://xenbits.xen.org/xsa/advisory-229.html
http://www.securitytracker.com/id/1039176
http://www.securityfocus.com/bid/100343