Date: Tue, 12 Dec 2017 12:00:14 +0000 From: Xen.org security team <security@....org> To: xen-announce@...ts.xen.org, xen-devel@...ts.xen.org, xen-users@...ts.xen.org, oss-security@...ts.openwall.com CC: Xen.org security team <security-team-members@....org> Subject: Xen Security Advisory 251 - improper bug check in x86 log-dirty handling -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory XSA-251 version 2 improper bug check in x86 log-dirty handling UPDATES IN VERSION 2 ==================== Public release. Provide information for Xen 4.10-in-preparation branch in .meta. ISSUE DESCRIPTION ================= 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). IMPACT ====== A malicious or buggy PV guest may cause a hypervisor crash, resulting in a Denial of Service (DoS) affecting the entire host. VULNERABLE SYSTEMS ================== 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). MITIGATION ========== Running only HVM guests avoids the vulnerability. Avoiding live migration of x86 PV guests also avoids the vulnerability. CREDITS ======= This issue was discovered by Jan Beulich of SUSE. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa251.patch xen-unstable, Xen 4.9.x xsa251-4.8.patch Xen 4.8.x, Xen 4.7.x, Xen 4.6.x xsa251-4.5.patch Xen 4.5.x $ sha256sum xsa251* 152cf5c88c3e441af01cdf5749877cabb6ab961afee9f29ae3077e725b703aa2 xsa251.meta 0dfbcfe459f051abb571d3fbedbe9760a4c6cd540ab5d525627050e3eeb9234e xsa251.patch 345a6e004e0d0d89c7fc8db55d48d68f53402a521bd1aa3cb4168043e1ae5673 xsa251-4.5.patch f8cecf013a3628038e0a4566778852a560b25a1ce2f3872a989087ab2fc9a913 xsa251-4.8.patch $ 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 administrators. 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 Team. (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.) For more information about permissible uses of embargoed information, consult the Xen Project community's agreed Security Policy: http://www.xenproject.org/security-policy.html -----BEGIN PGP SIGNATURE----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAlovuNkMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZvOgIALWR2TD54KrdAAtdp0q6b9eo4VcMi5BACeuOIxoY Ek0YA8CLVhj/zmT4/JFH8hZl4Jq0YkWCmxieAw8RvvzFD8WjS7CjTGjseYLL39rZ tyz+GTJ4ws1AVm/HL0JcYqoIWHv3I5M1OdoEKcAyYt4qoHTC00YtQFoSz0Gkruk0 37OMyAfSo3ex+YUpN4S5RXnXB0gdvIOnZJU2WAYYsXxncsOXSP87ohiK55QfK3zO HcSPbcux/NonLG1KqFGzEIXq3wFv1hXo9MGdKnmoeTkr0uaGjxxWySbTyZ5pPzXD Vyr6/W5GwQjee/48KzYEr/UggfeutUpYfSVnW/KL/CCqqy0= =sgSx -----END PGP SIGNATURE----- Download attachment "xsa251.meta" of type "application/octet-stream" (2407 bytes) Download attachment "xsa251.patch" of type "application/octet-stream" (680 bytes) Download attachment "xsa251-4.5.patch" of type "application/octet-stream" (760 bytes) Download attachment "xsa251-4.8.patch" of type "application/octet-stream" (666 bytes)
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