Date: Thu, 06 Feb 2014 12:38:51 +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 85 - Off-by-one error in FLASK_AVC_CACHESTAT hypercall -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory XSA-85 version 2 Off-by-one error in FLASK_AVC_CACHESTAT hypercall UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= The FLASK_AVC_CACHESTAT hypercall, which provides access to per-cpu statistics on the Flask security policy, incorrectly validates the CPU for which statistics are being requested. IMPACT ====== An attacker can cause the hypervisor to read past the end of an array. This may result in either a host crash, leading to a denial of service, or access to a small and static region of hypervisor memory, leading to an information leak. VULNERABLE SYSTEMS ================== Xen version 4.2 and later are vulnerable to this issue when built with XSM/Flask support. XSM support is disabled by default and is enabled by building with XSM_ENABLE=y. Only systems with the maximum supported number of physical CPUs are vulnerable. Systems with a greater number of physical CPUs will only make use of the maximum supported number and are therefore vulnerable. By default the following maximums apply: * x86_32: 128 (only until Xen 4.2.x) * x86_64: 256 These defaults can be overridden at build time via max_phys_cpus=N. The vulnerable hypercall is exposed to all domains. MITIGATION ========== Rebuilding Xen with more supported physical CPUs can avoid the vulnerability; provided that the supported number is strictly greater than the actual number of CPUs on any host on which the hypervisor is to run. If XSM is compiled in, but not actually in use, compiling it out (with XSM_ENABLE=n) will avoid the vulnerability. CREDITS ======= This issue was discovered by Matthew Daley. RESOLUTION ========== Applying the attached patch resolves this issue. xsa85.patch xen-unstable, Xen 4.3.x, Xen 4.2.x $ sha256sum xsa85*.patch 20571024e6815eeb40d2f92a3d70ae699047cffafb5431ec74b652e0843a5315 xsa85.patch $ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQEcBAEBAgAGBQJS84H+AAoJEIP+FMlX6CvZXy8H/An+HT3e3Av9G3PWIv+i10O3 FE7fhT53tBCbDlcqDghoO9PE6YctWV8glJHdg5TfpzXkjbVL2Go/poUhwvVqxePj ja5x5saXHvXoKwglc7sZmryil5bhecTKspNL5AfTlvP4dyNZMnOAvlbnyCtKUS45 bH0TSonTL50yRH1tCEaIKYDnOisIk3E5yduIpkRnqwamKw+DbHMGlmq5sPZq4rLH EYa/yhqh4bDStGAlRuBHG8ms+F7SgxH8dTjXhCbTe5BeAxYg1cP5yGX61y14xJJt KAObUS4E1KOcP1jRWIQ1HhHQxwWwEDdRk+ZQspGuIt34hY1SfMcbpFu7LutcI4Y= =SiDW -----END PGP SIGNATURE----- Download attachment "xsa85.patch" of type "application/octet-stream" (948 bytes)
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