Date: Wed, 21 Dec 2016 12:01:30 +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 202 (CVE-2016-10024) - x86 PV guests may be able to mask interrupts -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2016-10024 / XSA-202 version 3 x86 PV guests may be able to mask interrupts UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= Certain PV guest kernel operations (page table writes in particular) need emulation, and use Xen's general x86 instruction emulator. This allows a malicious guest kernel which asynchronously modifies its instruction stream to effect the clearing of EFLAGS.IF from the state used to return to guest context. IMPACT ====== A malicious guest kernel administrator can cause a host hang or crash, resulting in a Denial of Service. VULNERABLE SYSTEMS ================== All Xen versions are vulnerable. Only x86 PV guests can exploit the vulnerability. Neither ARM guests nor x86 HVM guests can exploit the vulnerability. MITIGATION ========== Running only HVM guests will avoid the vulnerability. For PV guests 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 Jan Beulich of SUSE. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa202.patch xen-unstable, Xen 4.8.x, Xen 4.7.x xsa202-4.6.patch Xen 4.6.x, Xen 4.5.x xsa202-4.4.patch Xen 4.4.x $ sha256sum xsa202* 057be742acfef200ba6f094a5dce486dd1c4e15013afe3efc963523ce2ec9cbb xsa202.patch cd53dc8b761dc7eb60998ea2419c98af926aa62b4317dbef15f597f5554f9015 xsa202-4.4.patch e007187639f5392a9256979504d50eff0ae38309a61524ea42c4150fab38b6f4 xsa202-4.6.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 iQEcBAEBAgAGBQJYWm8TAAoJEIP+FMlX6CvZlekIALNmG5XBvAvY3Hpjwr/h+bh6 AJNof+4jH7WUsyV8NyJxBOtAxDBeGsQ5csoryIt8CoqPfL6lph5Y0eUMAa+aOGYB FyMtWlKhyhoCjXcxhBCSAuHKldXyroZtzb6mx01nZSC8PbOCrnRzIGm/JLlnVS7b WBol9ID3DRWlI42gwpzDh3l/64Rioyyk1I26Kqal56+CT9iPk/b2UwqVb9oGQPI0 iq8Lki5NAKwOQdRxQKEFnWMuwK2bJsuayM3K0Cl/DBckvcOstMkP543btZDZA/Uy AiAOrTcBeDPmOoUVRpjwNEsFiiNeGgXV1R+FOcoZfWLdTKsn2igOtUkEekwVdAs= =SNhC -----END PGP SIGNATURE----- Download attachment "xsa202.patch" of type "application/octet-stream" (2691 bytes) Download attachment "xsa202-4.4.patch" of type "application/octet-stream" (2265 bytes) Download attachment "xsa202-4.6.patch" of type "application/octet-stream" (2535 bytes)
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