Date: Thu, 29 Oct 2015 12:00:23 +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 147 (CVE-2015-7814) - arm: Race between domain destruction and memory allocation decrease -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2015-7814 / XSA-147 version 3 arm: Race between domain destruction and memory allocation decrease UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= While freeing the memory associated with a domain during domain destruction Xen could race with a toolstack domain reducing the amount of memory associated with that same domain via the XENMEM_decrease_reservation. In the case where this race is hit the host will crash. The race is not exposed via the XENMEM_remove_from_physmap or XENMEM_exchange interfaces. IMPACT ====== Domains deliberately given partial management control may be able to deny service by crashing the host. Such a domain needs to be granted access to at least one of XENMEM_decrease_reservation or XEN_DOMCTL_destroydomain over another domain. As a result, in a system designed to enhance security by radically disaggregating the management, the security may be reduced. But, the security will be no worse than a non-disaggregated design. VULNERABLE SYSTEMS ================== This issue is only relevant to systems which intend to increase security through the use of advanced disaggregated management techniques. This does not include systems using libxl, libvirt, or OpenStack (unless substantially modified or supplemented, as compared to versions supplied by the respective upstreams). Only ARM systems are potentially affected. All Xen versions which support ARM are potentially affected. x86 systems are not affected. MITIGATION ========== There is no known mitigation. Switching from disaggregated to a non-disaggregated operation does NOT mitigate these vulnerabilities. Rather, it simply recategorises the vulnerability to hostile management code, regarding it "as designed"; thus it merely reclassifies these issues as "not a bug". Users and vendors of disaggregated systems should not change their configuration. CREDITS ======= This issue was discovered by Ian Campbell of Citrix. RESOLUTION ========== Applying the attached patch resolves this issue. xsa147.patch xen-unstable, Xen 4.6.x, Xen 4.5.x, Xen 4.4.x $ sha256sum xsa147*.patch 35cd9c5dabd5af6756957cf7378d527b2fcbff35dcf578769769a364a98ea6ac xsa147.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) iQEcBAEBAgAGBQJWMgm3AAoJEIP+FMlX6CvZHPAIAIgXu4741IJeO/Pb187gxO3Z IXpSSJF1Fvof/Ma6LLSGRth94WiafF91MKKqlEAKFPyfRUOkJXHAoahDUe7lF1Lr V5qSA4jAu69ZIhg3AAKuI+xBV/PNx7rlaG0duRI9nHmLRhbIU3EF9YJbKntdZzZr gdE/zLk+moW4U2/quEIEQGqtDGr/RAm5N0MqGwW4mcHUhlp4XcNuqrC8+b5qaeJ3 8/pc9whzyHM04De5Ve9/iFUu0J6KxNK+hN9V14mO8bcPXzK/K8X4C3qUD6HtZx+U VsaKT/N4INNDg7wqULcjg/Vp23SE/mUPM8Fernee9KnI2CY3pnS9DB1KEYMry5s= =7g7l -----END PGP SIGNATURE----- Download attachment "xsa147.patch" of type "application/octet-stream" (1566 bytes)
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