Memory sharing, available to x86 HVM guests only, uses a special value
in the global machine to physical address translation table (M2P). PV
guests have full control over M2P entries corresponding to pages they
own. A bug check (specifically, an assertion that an M2P entry is not
the special "shared" indicator) was insufficiently qualified, and as a
consequence is triggerable by PV guests in log-dirty mode
(e.g. because of being live migrated).
A malicious or buggy PV guest may cause a hypervisor crash, resulting in
a Denial of Service (DoS) affecting the entire host.
Xen versions 4.0 and later are affected. Xen versions 3.4 and earlier
are not affected.
Only x86 systems are vulnerable. ARM systems are not vulnerable.
x86 HVM guests cannot exploit this vulnerability.
Only x86 PV guests can exploit this vulnerability, and only when being
run in shadow mode. PV guests are typically run in shadow mode for live
migration, as well as for features like VM snapshot.
Note that save / restore does *not* use shadow mode, and so does not
expose this vulnerability. Some downstreams also include a "non-live
migration" feature, which also does not use shadow mode (and thus does
not expose this vulnerability).
Running only HVM guests avoids the vulnerability.
Avoiding live migration of x86 PV guests also avoids the vulnerability.
Name: the Xen project
Upstream: Jan Beulich (SUSE)
Created xen tracking bugs for this issue:
Affects: fedora-all [bug 1525018]