Date: Thu, 18 Apr 2013 13:36:19 +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 44 (CVE-2013-1917) - Xen PV DoS vulnerability with SYSENTER -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2013-1917 / XSA-44 version 2 Xen PV DoS vulnerability with SYSENTER UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= The SYSENTER instruction can be used by PV guests to accelerate system call processing. This instruction, however, leaves the EFLAGS register mostly unmodified - in particular, the NT flag doesn't get cleared. If the hypervisor subsequently uses IRET to return to the guest (which it will always do if the guest is a 32-bit one), that instruction will cause a #GP fault to be raised, but the recovery code in the hypervisor will again try to use IRET without intermediately clearing the NT flag. The #GP fault raised on this second IRET is a fatal event, causing the hypervisor to crash. IMPACT ====== Malicious or buggy unprivileged user space can cause the entire host to crash. VULNERABLE SYSTEMS ================== All 64-bit Xen versions from 3.1 onwards running on Intel CPUs are vulnerable. 32-bit Xen is not affected, as it doesn't permit the use of SYSENTER by PV guests. 64-bit Xen run on AMD CPUs isn't affected since AMD CPUs don't allow the use of SYSENTER in long mode. The vulnerability is only exposed by PV guests. MITIGATION ========== Running only HVM guests, or running PV guests on only 32-bit hosts or only AMD CPUs will avoid this vulnerability. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa44-4.1.patch Xen 4.1.x xsa44-4.2.patch Xen 4.2.x xsa44-unstable.patch xen-unstable $ sha256sum xsa44*.patch 3dbf47224be0f8fc66ba08d8a46b910bd9a3e672ffe864aa77c698bef0e27783 xsa44-4.1.patch c6c3afa228426d78e0484b7ac34210f642f79add35c4a04ca5ff7db5f2539e49 xsa44-4.2.patch 0e6ad83da75dc207a165411844c0985fd7f9588d92c2c95911c245485351bf36 xsa44-unstable.patch $ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBAgAGBQJRb/ZcAAoJEIP+FMlX6CvZCwMH/iTJCG4P9d+0nADT6YB3JmPl e9eO+cE+rGHBy5pdKAh1UF1JG9VvQe76hlJP3YS0QaXMNtN6k2dxoHZEj1hpSzKJ Q+KfS/R9yvVlputbfsVPSYYTl1bzDzMlWqyy/cZUZZVpGkMhVw1dLjJp4NvohCWb OABvchlbY1tW2Vk4tNWy4vhVGHdzxegrtttEuAIBoXHtCIIeH3/0nwqokahfKzog cKr5+y9K0JgbFSGP25POu/e7s9+sUKjJfUsFVw3+HknBW+zgJZ8fcu+/J0eJlgb5 0tkq749p+DtRE+kqS4sSM71+iGmnpWh+a0lsBmhARa6pyKVN+ccMvzvh809ItQg= =w315 -----END PGP SIGNATURE----- Download attachment "xsa44-4.1.patch" of type "application/octet-stream" (2844 bytes) Download attachment "xsa44-4.2.patch" of type "application/octet-stream" (2843 bytes) Download attachment "xsa44-unstable.patch" of type "application/octet-stream" (1670 bytes)
Powered by blists - more mailing lists
Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.