Date: Tue, 08 May 2018 17:00:22 +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-team-members@....org> Subject: Xen Security Advisory 262 - qemu may drive Xen into unbounded loop -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory XSA-262 version 2 qemu may drive Xen into unbounded loop UPDATES IN VERSION 2 ==================== Public release. Updated .meta file ISSUE DESCRIPTION ================= When Xen sends requests to a device model, the next expected action inside Xen is tracked using a state field. The requests themselves are placed in a memory page shared with the device model, so that the device model can communicate to Xen its progress on the request. The state field is in the request itself, where the device model may write to it. Xen correctly rejects invalid state values, but failed to reject invalid transitions between states. As a result, a device model which switches a request between two states at the right times can drive Xen into an unbounded loop. IMPACT ====== A malicious unprivileged device model can cause a Denial of Service (DoS) affecting the entire host. Specifically, it may prevent use of a physical CPU for an indeterminate period of time. VULNERABLE SYSTEMS ================== All Xen versions are vulnerable. Only x86 systems are affected. ARM systems are not affected. Only HVM guests can expose this vulnerability. PV and PVH guests cannot expose this vulnerability, but note that the domains being able to leverage the vulnerability are PV or PVH ones, running the device model. This vulnerability is only applicable to Xen systems using stub domains. MITIGATION ========== Running only PV or PVH guests will avoid this issue. (The security of a Xen system using stub domains is still better than with a qemu-dm running as an unrestricted dom0 process. Therefore users with these configurations should not switch to an unrestricted dom0 qemu-dm.) CREDITS ======= This issue was discovered by Jan Beulich of SUSE. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa262.patch xen-unstable xsa262-4.10.patch Xen 4.10.x xsa262-4.9.patch Xen 4.9.x, Xen 4.8.x, Xen 4.7.x xsa262-4.6.patch Xen 4.6.x $ sha256sum xsa262* a5a3458c5efdad282bd769fcab2b94ebfe0a979befae3b4703201fcbf0970cc7 xsa262.meta 5aa73753d3eec8ae391b1364c430df7517bf4bdb3e65a8e6e8431898348f4ad9 xsa262.patch 7196b468b916bf956f8dc0cab20a5c29f8a1bfa4de4e4fa982b7b9c8494e4c0d xsa262-4.6.patch ec2b6ba9ed1d5e97fed4b54767160a75fe19d67e4519f716739bebdb78816191 xsa262-4.9.patch 91d3b329131b6d434b268c0c55fd4900033fce8b2582bd9278ae967efc980fb0 xsa262-4.10.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 iQEcBAEBCAAGBQJa8dQhAAoJEIP+FMlX6CvZyCUH/1eCZrElPEOUySjMRbix0EJ8 TW5pWx76PX27Hek4fk+tFxsfDWEqWN4AP9YgjSQKNyXUWEr1oiyq83Vq/JXM6bHt HSWbrh7sjkkziEGqlOXpryS8/RIE3CZC5nQOTAsPX65tB+2nXkOY5zwuxXM8Ivn6 9p0yitSWd3Ve68PLAhthb/7BDdsAgITtgtxuTDHmDB6h32Fo8m990nD1jbAcP9WR q32gqXUMdlCf161/viPkSnrRqsnmdzPbXDsAzqtnUeVGNtqb5mI8jqox9Z6JGedG qMwlZVWO7TzcpO/18KbI8qYypL2/ensEo4bPbvRN7qzA6y8QGwMrLsygtZuBVkw= =D72A -----END PGP SIGNATURE----- Download attachment "xsa262.meta" of type "application/octet-stream" (1819 bytes) Download attachment "xsa262.patch" of type "application/octet-stream" (2986 bytes) Download attachment "xsa262-4.6.patch" of type "application/octet-stream" (2736 bytes) Download attachment "xsa262-4.9.patch" of type "application/octet-stream" (2738 bytes) Download attachment "xsa262-4.10.patch" of type "application/octet-stream" (2748 bytes)
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