An issue was discovered in Xen through 4.13.x, allowing guest OS users to cause a denial of service because of a bad error path in GNTTABOP_map_grant. Grant table operations are expected to return 0 for success, and a negative number for errors. Some misplaced brackets cause one error path to return 1 instead of a negative value. The grant table code in Linux treats this condition as success, and proceeds with incorrectly initialised state. A buggy or malicious guest can construct its grant table in such a way that, when a backend domain tries to map a grant, it hits the incorrect error path. This will crash a Linux based dom0 or backend domain.
https://xenbits.xen.org/xsa/advisory-316.html
https://www.debian.org/security/2020/dsa-4723
https://security.gentoo.org/glsa/202005-08
http://xenbits.xen.org/xsa/advisory-316.html
http://www.openwall.com/lists/oss-security/2020/04/14/3
http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00006.html