Advisory: XSA-224

XSA-224 has multiple CVEs assigned. This testcase exercises CVE-2017-10920 specifically.

When a grant is mapped with both host and device mappings as being writeable, and unmapped with two separate unmap hypercalls, one too many references are dropped. This causes Xen to loose track of one writeable mapping.

See also: tests/xsa-224/main.c