From ${URL} : Xen Security Advisory XSA-61 libxl partially sets up HVM passthrough even with disabled iommu ISSUE DESCRIPTION ================= With HVM domains, libxl's setup of PCI passthrough devices does the IOMMU setup after giving (via the device model) the guest access to the hardware and advertising it to the guest. If the IOMMU is disabled the overall setup fails, but after the device has been made available to the guest; subsequent DMA instructions from the guest to the device will cause wild DMA. IMPACT ====== A HVM domain, given access to a device which bus mastering capable in the absence of a functioning IOMMU, can mount a privilege escalation or denial of service attack affecting the whole system. VULNERABLE SYSTEMS ================== 1. Only systems which pass busmastering-capable PCI devices through to untrusted guests are vulnerable. (Most PCI devices are busmastering-capable.) 2. Only systems which use libxl as part of the toolstack are vulnerable. The major consumer of libxl functionality is the xl toolstack which became the default in Xen 4.2. In addition to this libvirt can optionally make use of libxl. This can be queried with # virsh version which will report "xenlight" if libxl is in use. libvirt currently prefers the xend backend if xend is running. The xend and xapi toolstacks do not currently use libxl. 3. Only Xen versions 4.0.x through 4.2.x are vulnerable. 4. Only HVM domains can take advantage of this vulnerability. 5. Systems which have a functioning IOMMU are NOT vulnerable. MITIGATION ========== This issue can be avoided by not assigning PCI devices to HVM guests when there is no functioning IOMMU. NOTE REGARDING LACK OF EMBARGO ============================== This issue was disclosed publicly on xen-devel; the person reporting it did not appreciate that it was a security issue. Additionally the patch to fix the issue was already applied to the respective branches (in particular resulting in Xen 4.3 not being vulnerable). Under the circumstances the Xen.org security team do not consider that this advisory should be embargoed. Also, we apologise for the delay to this advisory message, which was due to an oversight by us. CREDITS ======= George Dunlap found the issue as a bug, which on examination by the Xenproject.org Security Team turned out to be a security problem. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa61-4.1.patch Xen 4.1.x xsa61-4.2-unstable.patch Xen 4.2.x, xen-unstable @maintainer(s): after the bump, in case we need to stabilize the package, please say explicitly if it is ready for the stabilization or not.
this is fixed in xen-4.2.3
CVE-2013-4329 (http://nvd.nist.gov/nvd.cfm?cvename=CVE-2013-4329): The xenlight library (libxl) in Xen 4.0.x through 4.2.x, when IOMMU is disabled, provides access to a busmastering-capable PCI passthrough device before the IOMMU setup is complete, which allows local HVM guest domains to gain privileges or cause a denial of service via a DMA instruction.
see comment#1, this is already fixed in >=xen-4.3.2, so no in tree versions are affected. thanks
Arches and Mainter(s), Thank you for your work. Added to an existing GLSA request.
This issue was resolved and addressed in GLSA 201407-03 at http://security.gentoo.org/glsa/glsa-201407-03.xml by GLSA coordinator Mikle Kolyada (Zlogene).
