Date: Tue, 22 Nov 2016 12:02:12 +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@....org> Subject: Xen Security Advisory 192 (CVE-2016-9382) - x86 task switch to VM86 mode mis-handled -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2016-9382 / XSA-192 version 3 x86 task switch to VM86 mode mis-handled UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= LDTR, just like TR, is purely a protected mode facility. Hence even when switching to a VM86 mode task, LDTR loading needs to follow protected mode semantics. This was violated by the code. IMPACT ====== On SVM (AMD hardware): a malicious unprivileged guest process can escalate its privilege to that of the guest operating system. On both SVM and VMX (Intel hardware): a malicious unprivileged guest process can crash the guest. VULNERABLE SYSTEMS ================== Only 32-bit x86 HVM guests are vulnerable. Furthermore, only guest operating systems which actually make use of hardware task switching, and allow a new task to start in VM86 mode, are vulnerable. We are not aware of any such operating systems. The vulnerability is NOT exposed on any PV guests. The vulnerability is NOT exposed on any 64-bit guests, ARM systems are NOT vulnerable. Xen versions from 4.0 onwards are affected. Xen versions 3.4 and earlier are not affected. MITIGATION ========== For guests which are affected, the vulnerability could possibly be mitigated by disabling access to VM86 mode by unprivileged guest programs. Details would depend on the (so far hypothetical) vulnerable guest kernel. CREDITS ======= This issue was discovered by Jan Beulich of SUSE. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa192.patch xen-unstable, Xen 4.7.x, Xen 4.6.x xsa192-4.5.patch Xen 4.5.x, Xen 4.4.x $ sha256sum xsa192* 687b0216eefd5ecef8a3135cc6f542cb3d9ff35e8e9696a157703e84656c35e8 xsa192.patch bb0c6622c6f5c5eb9a680020d865802069446830b4a170bcb82336f6c3b77f55 xsa192-4.5.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----- Version: GnuPG v1 iQEcBAEBAgAGBQJYNDJ9AAoJEIP+FMlX6CvZy5gIALU7weBZNJeQzBUMoQn6fAG/ KNP3Br3BDYHC/MMbyIAkkEyHTfsR1xFNAHHb2Tb/Wl7v081owV7JwO3bkf0FJ88w K8RXFeUbt1z5rAdt1B088CbZA4/KkGRBd32vicUIE7+9EnkgSOlLc8abjind+yQ9 2CtOHwDL0LVbjjGF6VdME9pooDZf2ZT1fHfClUbwPFsfTMKjUeJcfoVFqenifmYR wTYPtw6z+cCrjBlPyleglh/2uAc6ncTIQAC8Ee2dJyKv4wMqP60u97ANylnN3DpZ DTl+VUYdNsy78R9/xbqF7dT5gCeDV9y1rDoqHQwwtSGL/lvjU0ujbEtG7XS2/7M= =chON -----END PGP SIGNATURE----- [ CONTENT OF TYPE application/octet-stream SKIPPED ] [ CONTENT OF TYPE application/octet-stream SKIPPED ]
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