Date: Thu, 18 Feb 2021 11:47:16 +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 366 v1 - missed flush in XSA-321 backport -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory XSA-366 missed flush in XSA-321 backport ISSUE DESCRIPTION ================= An oversight was made when backporting XSA-320, leading entries in the IOMMU not being properly updated under certain circumstances. IMPACT ====== A malicious guest may be able to retain read/write DMA access to frames returned to Xen's free pool, and later reused for another purpose. Host crashes (leading to a Denial of Service) and privilege escalation cannot be ruled out. VULNERABLE SYSTEMS ================== Xen versions up to 4.11, from at least 3.2 onwards, are affected. Xen versions 4.12 and newer are not affected. Only x86 Intel systems are affected. x86 AMD as well as Arm systems are not affected. Only x86 HVM guests using hardware assisted paging (HAP), having a passed through PCI device assigned, and having page table sharing enabled can leverage the vulnerability. Note that page table sharing will be enabled (by default) only if Xen considers IOMMU and CPU large page size support compatible. MITIGATION ========== Suppressing the use of page table sharing will avoid the vulnerability (command line option "iommu=no-sharept"). Suppressing the use of large HAP pages will avoid the vulnerability (command line options "hap_2mb=no hap_1gb=no"). Not passing through PCI devices to HVM guests will avoid the vulnerability. CREDITS ======= This issue was reported as a bug by M. Vefa Bicakci, and recognized as a security issue by Roger Pau Monne of Citrix. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. Note that patches for released versions are generally prepared to apply to the stable branches, and may not apply cleanly to the most recent release tarball. Downstreams are encouraged to update to the tip of the stable branch before applying these patches. xsa366-4.11.patch Xen 4.11.x $ sha256sum xsa366* 3131c9487b9446655e2e21df4ccf1e003bec471881396d7b2b1a0939f5cbae96 xsa366.meta 8c8c18ca8425e6167535c3cf774ffeb9dcb4572e81c8d2ff4a73fefede2d4d94 xsa366-4.11.patch $ NOTE REGARDING LACK OF EMBARGO ============================== This was reported and debugged publicly, before the security implications were apparent. -----BEGIN PGP SIGNATURE----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAmAuU5EMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZMCkIAKq1dU6xOMN3lFqY6LeIV+Pn+JQDvJKhDT+lJT9b KAP+a44ks5bHHSD6CPyiq5boU5APE7yqiyJnXBycXVDLH6GGjh7uBvc6A00YkeHU y08l8jxa6/FAyrvCj5P0pYItALwH0NZDtfUE57ueloYUu3KJnyBRtl9icvx/sCa9 CUkpKDpS0te+Rk+G57UPDjGvSPwpIh01vphJ5tyf+2Lrk8rsHTJYWQ7eD8A09jCr DtSD6FylzEuGGY30vPGLUzXgOm8Nji/WgnXnmmbILCEo8PQs3CcoxN53/F8cYvr6 NRERHKZFhHoLmUUCImoFcApxzzdt11USDnCdEXiAkrEOYsk= =w9OA -----END PGP SIGNATURE----- Download attachment "xsa366.meta" of type "application/octet-stream" (338 bytes) Download attachment "xsa366-4.11.patch" of type "application/octet-stream" (1512 bytes)
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