Date: Tue, 04 Apr 2017 12:37:14 +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@....org> Subject: Xen Security Advisory 212 (CVE-2017-7228) - x86: broken check in memory_exchange() permits PV guest breakout -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2017-7228 / XSA-212 version 3 x86: broken check in memory_exchange() permits PV guest breakout UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= The XSA-29 fix introduced an insufficient check on XENMEM_exchange input, allowing the caller to drive hypervisor memory accesses outside of the guest provided input/output arrays. IMPACT ====== A malicious or buggy 64-bit PV guest may be able to access all of system memory, allowing for all of privilege escalation, host crashes, and information leaks. VULNERABLE SYSTEMS ================== All Xen versions are vulnerable. Only x86 systems are affected. ARM systems are not vulnerable. The vulnerability is only exposed to 64-bit PV guests. HVM guests and 32-bit PV guests can't exploit the vulnerability. MITIGATION ========== Running only HVM or 32-bit PV guests will avoid the vulnerability. The vulnerability can be avoided if the guest kernel is controlled by the host rather than guest administrator, provided that further steps are taken to prevent the guest administrator 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 Jann Horn of Google Project Zero. RESOLUTION ========== Applying the attached patch resolves this issue. xsa212.patch xen-unstable, Xen 4.8.x, Xen 4.7.x, Xen 4.6.x, Xen 4.5.x, Xen 4.4.x $ sha256sum xsa212* be1255bcda06158cdb86eb5297e8a271e05318e88cd21035c58a67f9ada6ccba xsa212.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 iQEcBAEBAgAGBQJY45NxAAoJEIP+FMlX6CvZMRMH/jGfTS4hcPuPAiarYhD4D4YQ pVir0eM/gm/8yJE/CT3m3dieKjjl+GAFW4ehRMoIoxVdSlhiwskx5V+8I5qR/Lo6 6F9BPJw6eaEM62yw7YvMl7EuSexP3WgQeyRSf3BckZ0oxEPSHrIUi0/p0B7FNOFr C1EqK9d08dMKA5AEugpXgDI0t7fbYg3Kkm8SVnW5B8+5OI/iyTOOkFoPx1sbEvWX k+zgzodsDuoh8O25+pKVs+verknzGJm9UdCD7vHW8elLg1+1nS2BlfTSr478cDTE FnbnpuE7r1X/HHd2hPHDAZu3g2IUqfBJCLeYZfhIM9Eioei6bVLXh0f33DvlH/U= =L74k -----END PGP SIGNATURE----- Download attachment "xsa212.patch" of type "application/octet-stream" (3392 bytes)
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