[3.14] main/xen: add mitigations for XSA-407
https://xenbits.xen.org/xsa/advisory-407.html
About the xsa407-4.15-00.patch:
Upstream patches xsa407-4.15-*.patch are supposed to be applied after 505771bb1dffdf6f763fad18ee49a913b98abfea, inferred from xsa407.meta, at the time of this writing the thirteenth commit after the tip of the stable-4.15 branch. Since we don't want to "update Xen version to 4.15.4-pre" we choose the commit before that. The command to reproduce the above intermediate patch is:
git format-patch f6e26ce^..d470a54 --stdout > xsa407-4.15-00.patch
Edited by omni