Date: Thu, 29 Oct 2015 12:00:44 +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 152 (CVE-2015-7971) - x86: some pmu and profiling hypercalls log without rate limiting -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2015-7971 / XSA-152 version 3 x86: some pmu and profiling hypercalls log without rate limiting UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= HYPERCALL_xenoprof_op and HYPERVISOR_xenpmu_op log some errors and attempts at invalid operations. These log messages are not rate-limited, even though they can be triggered by guests. IMPACT ====== A malicious guest could cause repeated logging to the hypervisor console, leading to a Denial of Service attack. VULNERABLE SYSTEMS ================== Xen versions 3.2.x and later are affected. (The VPMU part of the vulnerability is applicable only to Xen 4.6 and later.) ARM systems are not affected. (The pmu hypercall is x86-specific, and xenoprof is not supported on ARM.) MITIGATION ========== The problematic log messages are issued with priority Warning. Therefore they can be rate limited by adding "loglvl=error/warning" to the hypervisor command line or suppressed entirely by adding "loglvl=error". On systems where the guest kernel is controlled by the host rather than guest administrator, running only kernels which do not call these hypercalls will also prevent untrusted guest users from exploiting this issue. However untrusted guest administrators can still trigger it unless further steps are taken to prevent them from loading code into the kernel (e.g. by disabling loadable modules etc) or from using other mechanisms which allow them to run code at kernel privilege. CREDITS ======= This issue was discovered by Jan Beulich of SUSE. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa152-unstable.patch xen-unstable, Xen 4.6.x xsa152-4.5.patch Xen 4.5.x, Xen 4.4.x, Xen 4.3.x $ sha256sum xsa152*.patch 596f51797aa591b5abd068ead03e21215cf70997c98a4a562392499afe47b81c xsa152.patch 7ae2811ea80da29ee234ad5a2cbb5908e03db8fb6c50774d378d77d273e74e39 xsa152-4.5.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 v1.4.12 (GNU/Linux) iQEcBAEBAgAGBQJWMgm/AAoJEIP+FMlX6CvZzPwIAJs/NTew5AJA3bTO6QZtVC2T sRt2F11prjjeklrAcqSC03q2bBpyylLB6PJ1jmmtT0MKtST5BszGA+sJt3G8nxw1 XKN8zNX5Yzfmltgi6ZeWk/1ps6kceb4evhkIUzt1v8Ttge148rEedGrJD9eLeRht XdZr8ujXwP3NGBAesKNf0DugPTR7diYyUzvwven+OXVPg0ZT53t1r6Xref7Vl4p6 5b9uOK3rh/QVRbPGTOA1vzObk0MssBTGA615JGG0da4fr4vVUQsVK/MV/N6oc4fJ iUHUcH83ldLGB9kt3+kq1S6KBESInriytPrKxNFvaKOrPlaOTOKRGvJSW0QZpos= =BsWE -----END PGP SIGNATURE----- Download attachment "xsa152.patch" of type "application/octet-stream" (2404 bytes) Download attachment "xsa152-4.5.patch" of type "application/octet-stream" (1443 bytes)
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