x86: incorrect error handling for guest p2m page removals
UPDATES IN VERSION 2
The internal function querying a domain's p2m table grabs the p2m lock
by default, so that the answer to the query remains true until the
caller can act on that information; it is up to the caller then to
release the lock. Unfortunately, certain failure paths don't release
A malicious or buggy guest may cause a deadlock, resulting in a DoS
(Denial of Service) affecting the entire host.
Xen 4.11 and onward are vulnerable.
Only x86 systems are vulnerable. ARM systems are not vulnerable.
Only systems running untrusted HVM or PVH guests are vulnerable.
Systems running only PV guests are not vulnerable.
Running only PV guests will avoid this vulnerability.
This issue was discovered by Paul Durrant of Citrix.
Applying the appropriate attached patch resolves this issue.
DEPLOYMENT DURING EMBARGO
Deployment of the patches and/or mitigations described above (or
others which are substantially similar) is permitted during the
embargo, even on public-facing systems with untrusted guest users and
But: Distribution of updated software is prohibited (except to other
members of the predisclosure list).
Predisclosure list members who wish to deploy significantly different
patches and/or mitigations, please contact the Xen Project Security
(Note: this during-embargo deployment notice is retained in
post-embargo publicly released Xen Project advisories, even though it
is then no longer applicable. This is to enable the community to have
oversight of the Xen Project Security Team's decisionmaking.)