Date: Fri, 25 Oct 2019 11:10:31 +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 285 v3 (CVE-2019-17341) - race with pass-through device hotplug -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2019-17341 / XSA-285 version 3 race with pass-through device hotplug UPDATES IN VERSION 3 ==================== CVE assigned. ISSUE DESCRIPTION ================= When adding a passed-through PCI device to a domain after it was already started, IOMMU page tables may need constructing on the fly. For PV guests the decision whether a page ought to have a mapping is based on whether the page is writable, to prevent IOMMU access to things like page tables. Writablility of a page may, however, change at any time. Failure of the relevant code to respect this possible race may lead to IOMMU mappings of, in particular, page tables, allowing the guest to alter such page tables without Xen auditing the changes. IMPACT ====== Malicious PV guests can escalate their privilege to that of the hypervisor. VULNERABLE SYSTEMS ================== All versions of Xen are vulnerable. Only x86 systems are vulnerable. ARM systems are not vulnerable. Only x86 PV guests can exploit the vulnerability. x86 HVM and PVH guests cannot exploit the vulnerability. Only guests which are assigned a device after domain creation can exploit this vulnerability. Guests which are not assigned devices, or guests assigned devices at domain creation time, cannot exploit this vulnerability. MITIGATION ========== Running only HVM or PVH guests avoids the vulnerability. Assigning passed-through PCI devices to PV guests at domain creation time also avoids the vulnerability. CREDITS ======= This issue was discovered by Jan Beulich of SUSE. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa285.patch xen-unstable xsa285-4.11.patch Xen 4.7.x - Xen 4.11.x $ sha256sum xsa285* 0851a4a9120220e2b03eafaf94648077154b6a6f27c29055d3779ccad7684fce xsa285.meta 9e96d3763158edde8d664c3e26761e63ca6f96bb921e0d7eb68351fe47499bde xsa285.patch 38ec20b04e0a859abe9850803ae00a33e48591a9949e5287dfa3725f3bd179f3 xsa285-4.11.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/4UyVfoK9kFAl2y178MHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZnhUIALWg5ROzP7vpvNOEQDICm/A/AxjPLB6uHnj95bBJ CxfLZPZyxUak9jmn8bJJrhJBNGS/RFUWrwWm+mHku8ywNKTcHkhGtweS8/GjuMeG I7hhh/Ux39vs/kPWvy7uydMIMrcIsiG69NWXl6xWMGkcmcmlkJCAi2KHX20Jb5qi Izy7swNoBFWuuGMaBTg8YJ+XfqQGonemzgviY01EHQqJo/2wPyJjgsbZzu6XlNJc R3K9K4RDzjtemIEQps9CWA8ilEXxv6DIhVKBx0gNLIrJZPVEh2awLr5Ve2YZIdk6 N5hSP2LFyueDhmKvwrMnrrKF4XqHlfyIsW0l8TXwa/OUTVI= =6noj -----END PGP SIGNATURE----- Download attachment "xsa285.meta" of type "application/octet-stream" (1723 bytes) Download attachment "xsa285.patch" of type "application/octet-stream" (2148 bytes) Download attachment "xsa285-4.11.patch" of type "application/octet-stream" (2077 bytes)
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