Xen Security Advisory 259 - x86: PV guest may crash Xen with XPTI
-----BEGIN PGP SIGNED MESSAGE-----
Xen Security Advisory XSA-259
x86: PV guest may crash Xen with XPTI
UPDATES IN VERSION 2
The workaround for the Meltdown vulnerability (XSA-254) failed to deal
with an error code path connecting the INT 80 handling with general
exception handling. This results in an unconditional write attempt of
the value zero to an address near 2^64, in cases where a PV guest has no
handler installed for INT 80 on one of its vCPU-s.
A malicious or buggy guest may cause a hypervisor crash, resulting in
a Denial of Service (DoS) affecting the entire host.
All Xen versions which the XSA-254 fixes were applied to are vulnerable.
Only x86 systems are vulnerable. ARM systems are not vulnerable.
Only x86 PV guests can exploit the vulnerability. x86 PVH and HVM
guests cannot exploit the vulnerability.
Running only PVH or HVM guests avoids the vulnerability.
This issue was discovered by Andrew Cooper 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is then no longer applicable.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.)