Date: Tue, 31 Mar 2015 12:09:52 +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 125 (CVE-2015-2752) - Long latency MMIO mapping operations are not preemptible -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2015-2752 / XSA-125 version 3 Long latency MMIO mapping operations are not preemptible UPDATES IN VERSION 3 ==================== CVE assigned. Public release. ISSUE DESCRIPTION ================= The XEN_DOMCTL_memory_mapping hypercall allows long running operations without implementing preemption. This hypercall is used by the device model as part of the emulation associated with configuration of PCI devices passed through to HVM guests and is therefore indirectly exposed to those guests. This can cause a physical CPU to become busy for a significant period, leading to a host denial of service in some cases. If a host denial of service is not triggered then it may instead be possible to deny service to the domain running the device model, e.g. domain 0. This hypercall is also exposed more generally to all toolstacks. However the uses of it in libxl based toolstacks are not believed to open up any avenue of attack from an untrusted guest. Other toolstacks may be vulnerable however. IMPACT ====== The vulnerability is exposed via HVM guests which have a PCI device assigned to them. A malicious HVM guest in such a configuration can mount a denial of service attack affecting the whole system via its associated device model (qemu-dm). A guest is able to trigger this hypercall via operations which it is legitimately expected to perform, therefore running the device model as a stub domain does not offer protection against the host denial of service issue. However it does offer some protection against secondary issues such as denial of service against dom0. VULNERABLE SYSTEMS ================== The issue is exposed via x86 HVM VMs which have been assigned a PCI device. x86 PV domains, x86 HVM domains without passthrough devices and ARM domains do not expose this vulnerability. Xen 3.2.x and later are vulnerable. Xen 3.1.x and earlier have not been inspected. MITIGATION ========== Running only PV guests will avoid this issue. This issue can be avoided by not assigning devices with large MMIO regions to untrusted HVM guests. CREDITS ======= This issue was discovered by Konrad Rzeszutek Wilk of Oracle. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa125.patch Xen 4.5.x, xen-unstable xsa125-4.4.patch Xen 4.4.x xsa125-4.3.patch Xen 4.3.x xsa125-4.2.patch Xen 4.2.x $ sha256sum xsa125*.patch be0c7cceb1af4b7b1341f37c1e20cf804ea3ac7d3c2ca2e5599f936479d5e0de xsa125.patch 5f081407c2955787c6e40daa847f3c4131694dff3bb0bc0ee55495f555c7bb52 xsa125-4.2.patch 3b0641ef2a23f12872267940c408097cb353e57a6e0396a64cdf13592a14f65b xsa125-4.3.patch 2180e657b34d8628d4e0157adf2a36904bb6feaf55d53338e4457ef77d867a31 xsa125-4.4.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) iQEcBAEBAgAGBQJVGo5JAAoJEIP+FMlX6CvZlEAIAMdSMKpxum+J9IbUFCqcHFa4 F8zQDkz2hMCY3OjTAq9+n6KR2LLyKDn2hGDP0Mspbo67lRBEjSkp7KEXCoDrA294 YsVuJn8y0T3yPH9du3m0f2vi49MrhnxnUZLNyKCpkxTiClrC/7JX3OZxQTQIGpzf EIsjYP+/w9ava5XYbGKorwlLvGpjRmnZpCDTrZlqKV2bK2O6pWzyvp5zD99FORcJ YVRIGebKu8szbSHZs9ectt4xkZwYrzSjj0+PtryvwLSpSYi0zTWIu9rrgd/ZCXfL tgD+i9zoc2E1ydPlvdKRXEdRHY9gGcaimfbTqYn1ttJ6qQcnbMoRQor4X+v92NU= =m83F -----END PGP SIGNATURE----- Download attachment "xsa125.patch" of type "application/octet-stream" (5547 bytes) Download attachment "xsa125-4.2.patch" of type "application/octet-stream" (5272 bytes) Download attachment "xsa125-4.3.patch" of type "application/octet-stream" (5249 bytes) Download attachment "xsa125-4.4.patch" of type "application/octet-stream" (5568 bytes)
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