Date: Tue, 26 Nov 2019 12:00:08 +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-team-members@....org> Subject: Xen Security Advisory 306 v2 - Device quarantine for alternate pci assignment methods -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory XSA-306 version 2 Device quarantine for alternate pci assignment methods UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= XSA-302 relies on the use of libxl's "assignable-add" feature to prepare devices to be assigned to untrusted guests. Unfortunately, this is not considered a strictly required step for device assignment. The PCI passthrough documentation on the wiki describes alternate ways of preparing devices for assignment, and libvirt uses its own ways as well. Hosts where these "alternate" methods are used will still leave the system in a vulnerable state after the device comes back from a guest. IMPACT ====== An untrusted domain with access to a physical device can DMA into host memory, leading to privilege escalation. VULNERABLE SYSTEMS ================== Only systems where guests are given direct access to physical devices capable of DMA (PCI pass-through) are vulnerable. Systems which do not use PCI pass-through are not vulnerable. Only systems which use "alternate" methods to assign devices to pciback before assignment are vulnerable. These methods include: - Assigning devices on the Linux command-line using `xen-pciback.hide` - Assigning devices via xen-pciback module parameters - Assigning devices manually via sysfs - Assigning devices using libvirt Systems which use `xl pci-assignable-add` or libxl_device_pci_assignable_add, or have the assignable state handled automatically via setting the `seize` parameter, are not affected. MITIGATION ========== For xl and libvirt, before assigning a device to a guest, manually run `xl pci-assignable-add`. This will quarantine the device even if the device has already been assigned to pciback by one of the alternate methods. This may also work for other libxl-based toolstacks, depending on the particular implementation. CREDITS ======= This issue was discovered by Marek Marczykowski-Górecki of Invisible Things Lab. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. Note that this patch will quarantine the device after the domain is destroyed by default. It must be un-quarantined before it can be used by domain 0 again. This can be done by executing `xl pci-assignable-remove`. This will be effective even if the device was assigned to pciback with one of the alternate methods. xsa306.patch xen-unstable xsa306-4.12.patch Xen 4.12.x xsa306-4.11.patch Xen 4.11.x, Xen 4.10.x xsa306-4.9.patch Xen 4.9.x, Xen 4.8.x $ sha256sum xsa306* 07468dcdfbe34b794fd0618bce7d6d1edb6b10b234dccf1e5dd1f1120a0affe7 xsa306.meta 3534ec46f03bb8dac3011e0e3739fc75400559078e4361bbe5385d97b7892650 xsa306.patch 426e32bfa7d7787fe6778685e623966f8762857f7920443a0ca73347df9d6624 xsa306-4.9.patch b00e58c9f96b0ff654dfd4904c675a54356148af718eb9b2adca0253b900dfc1 xsa306-4.11.patch 69857d08969903452fbf009905a145e06a5aef9966e969de9fbb22e62c557ffd xsa306-4.12.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----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAl3dE7EMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZdj0H/1MUzg8URNtE5FsG5Q0OwszcNXSuV1qW9B6mZCRJ ffGyGtTmhM2M/KXao9j15Hn83BVxTh5iFVkmZ9LoQSFiwu4L9nhx8KGw+nnspb9G v2+NrEbZRpxbloPxDplMfWLx1/GNFCs+wK550LtGC+yzITqMckacD6cTkbEGmIwR otLTU3JTlfwMnvhZraDzVrICyX/+vNri9EvHd7Tviz1yXk83QMapgZ+xJCocUY3n kA93XN2yG/xFB0jHky75wBT2HFRR1RpmLECSodiOP0ONLPJiRBl3O2ziqb8OtdRD mkMvTMWEJawTPiWKc5CS4ieD2YyiUngFC806r2LDpRk6468= =gi2B -----END PGP SIGNATURE----- Download attachment "xsa306.meta" of type "application/octet-stream" (1561 bytes) Download attachment "xsa306.patch" of type "application/octet-stream" (4180 bytes) Download attachment "xsa306-4.9.patch" of type "application/octet-stream" (3987 bytes) Download attachment "xsa306-4.11.patch" of type "application/octet-stream" (4080 bytes) Download attachment "xsa306-4.12.patch" of type "application/octet-stream" (4144 bytes)
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