Date: Thu, 29 Oct 2015 12:00:18 +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 146 (CVE-2015-7813) - arm: various unimplemented hypercalls log without rate limiting -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2015-7813 / XSA-146 version 3 arm: various unimplemented hypercalls log without rate limiting UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= The HYPERVISOR_physdev_op hypercall and most suboperations of the HYPERVISOR_hvm_op hypercall are not currently implemented by Xen on ARM and when called will log the use to the hypervisor console. However these guest accessible log messages are not rate-limited. IMPACT ====== A malicious guest could cause repeated logging to the hypervisor console, leading to a Denial of Service attack. VULNERABLE SYSTEMS ================== Xen 4.4 and later systems running on ARM hardware are vulnerable. x86 systems are not affected. MITIGATION ========== The problematic log messages are issued with priority Warning. Therefore they can be rate limited by adding "loglvl=error/warning" to the hypervisor command line or suppressed entirely by adding "loglvl=error". On systems where the guest kernel is controlled by the host rather than guest administrator, running only kernels 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. CREDITS ======= This issue was discovered by Julien Grall of Citrix. RESOLUTION ========== Applying the attached patch resolves this issue. xsa146.patch xen-unstable, Xen 4.6.x, Xen 4.5.x, Xen 4.4.x $ sha256sum xsa146*.patch 1d0ff203581ac5bcc0ec4469a4909da968b218ed83280efd217020c396028591 xsa146.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) iQEcBAEBAgAGBQJWMgm1AAoJEIP+FMlX6CvZGjMH/iYvPwiZU0iKkgADyMBek6A6 fmkHlmd5z7EC7eSwKn2SzRcw8KsE9E4Hdo4IaPoWx+ElSKlHwteo8vdHq3zYXWsb vpYFvlD5wiWRYpTDiBtDZC7cwOx1qqelDMwwN8k3p1g+eNqEB5VrfjVWWxp7xE6a +gqEea9+ASJmZ1K3cczOGIzWSrGSGcC7v715nECCwBkquYlsdP8L7I+K2IiCL45i ymRm+fD3CvDtLT+Q3ZG9I/C78CH5O4INATrdz6Syqtti+jPoYY7+6LmLZXR0tIk2 v47g/mAoDNwJAaWDfZL9GnzXTZIm+Lri+qh/4LkunnMGgHIF4Ah4HhsNJlX4h7M= =lDV8 -----END PGP SIGNATURE----- Download attachment "xsa146.patch" of type "application/octet-stream" (1248 bytes)
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