Date: Thu, 29 Oct 2015 12:00:38 +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 151 (CVE-2015-7969) - x86: leak of per-domain profiling-related vcpu pointer array -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2015-7969 / XSA-151 version 3 x86: leak of per-domain profiling-related vcpu pointer array UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= A domain's xenoprofile state contains an array of per-vcpu information, which is allocated once in the lifetime of a domain in response to that domain using the XENOPROF_get_buffer hypercall on itself or by a domain with the privilege to profile a target domain using the XENOPROF_set_passive hypercall. This array is leaked on domain teardown. This memory leak could -- over time -- exhaust the host's memory. IMPACT ====== The following parties can mount a denial of service attack affecting the whole system: - A malicious guest administrator via XENOPROF_get_buffer. - A domain given suitable privilege over another domain via XENOPROF_set_passive (this would usually be a domain being used to profile another domain, eg with the xenoprof tool). The ability to also restart or create suitable domains is also required to fully exploit the issue. Without this the leak is limited to a small multiple of the maximum number of vcpus for the domain. The maximum leak is 128kbytes per domain (re)boot. VULNERABLE SYSTEMS ================== Versions of Xen from 4.0 onwards are vulnerable. The XENOPROF hypercalls are only implemented on x86. ARM is therefore not vulnerable. MITIGATION ========== On systems where the guest kernel is controlled by the host rather than guest administrator, running only kernels (in the target and profiling domain respectively) 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. The leak is small. Preventing the creation of large numbers of new domains, and limiting the number of times an existing domain can be rebooted, can reduce the impact of this vulnerability. NOTE REGARDING CVE ================== Note that CVE-2015-7969 covers both this issue and XSA-149. CREDITS ======= This issue was discovered by Jan Beulich of SUSE. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. (To resolve CVE-2015-7969, the patch from XSA-149 is required too.) xsa151.patch xen-unstable, Xen 4.6.x, Xen 4.5.x, Xen 4.4.x, Xen 4.3.x $ sha256sum xsa151*.patch e247a9dbbe236ffa3c5aa5e2d41047fa67da80f2b0474eef3440b5b3da2d5617 xsa151.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the PATCH or the TRUSTED KERNEL MITIGATION (or others which are substantially similar) is permitted during the embargo, even on public-facing systems with untrusted guest users and administrators. However deployment of the (RE)BOOT LIMIT MITIGATION is NOT permitted (except where all the affected systems and VMs are administered and used only by organisations which are members of the Xen Project Security Issues Predisclosure List). Specifically, deployment on public cloud systems is NOT permitted. This is because applying domain creation and reboot limits in connection with a security issue would be a user-visible change which could lead to the rediscovery of the vulnerability. Deployment of the reboot mitigation is permitted only AFTER the embargo ends. Also: 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) iQEcBAEBAgAGBQJWMgm9AAoJEIP+FMlX6CvZticH+waAPTUnRA9CTnPs1BDjiTcc kBuVb8ouvffinj+FCVQ/CIC1IAkClU8vBcOb3NAe9/PaCYPe9OlAxpvAAxxlgr05 N1Py8rBUEemKcCS9T4jTT2TNLYm9lzFihcTMOp+Y2diavcdmnhXj+kjO/FpD7tG/ TRDBnCVsxA4m+yxQJO8xXWIE+lYCoF+42Qc8Dyi2tcaN4WaBjjD5DyqNHIuf1ISF DljnT3TsgDIlxmgeQsufX0VIh45FdZXExOmGAgRS3JCn0cTmQwONecyM5NjKaljZ LEwk5sMSRa4cmb8naJRxPf30CydjmLBMdzU8KRjg+d6M46jTGTV794k/AKc4VxI= =u9LH -----END PGP SIGNATURE----- Download attachment "xsa151.patch" of type "application/octet-stream" (767 bytes)
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