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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.0632 missed flush in XSA-321 backport 19 February 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Xen Publisher: Xen Operating System: UNIX variants (UNIX, Linux, OSX) Impact/Access: Increased Privileges -- Existing Account Denial of Service -- Existing Account Unauthorised Access -- Existing Account Reduced Security -- Existing Account Resolution: Patch/Upgrade Original Bulletin: http://xenbits.xen.org/xsa/advisory-366.html - --------------------------BEGIN INCLUDED TEXT-------------------- 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----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: https://www.auscert.org.au/bulletins/ =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBYC9FaeNLKJtyKPYoAQh7WA//VOre0JibB+gysd9oduCq50P2a30LdZPe RquYb84iDBzdz1wvK7jBh8xyzKCNXt149jC420sunL7PsKjvFbx2G6KJ6yOgr6ww kvanlxEqtlJ+3q+oUlywo0lwrH3UsKtNc9VvwecbawBP9glw0rLrG15gXcUV8JeY WZ7HbxEwb4QM3epCuCFx0wpLhm59UVcM22hOhachR+YVhspAavYnlD0n1mZU4NJx nUHwjiaAp9rR76hFCNRsRKZm+WS/ho8CNoAv/3aWD2b/s/p5+eHbUMGFbu+Qpb63 HbQOP2Q60STsaEOkuWpXNwUhS8bQALB1Y/EidJcBbxr9OiT9lQI7hcYyvgBYp9Hz FkITH19STY4lavmCi0OKelmKNnwK9+2B9TzY2+wQIHe1TZTGAUhOGNR88vUdQHPV Td3+l6Tkxf8v54Rjp64GLtIDVjOUAsh7o21c2ydj9PBivkQR/E89e5XMzj4AbGKF P2etHKSpvo6AdydtqcoWmnpALHw1XYDMNw/VDUufKxxUltspIp3dzZiHxaOSPqbi Fz2ekCOcOh3JUWRU3pbg4HT1tnJCxy75zcFNHPwTbgWluNVerrM/K3mfTfheb56T b1A87RkvlI1WhI53VLYm65/VtG9lExlueD3vsekGU20mLn1eQcGgVJkFtdJyi5O/ PmWxATvX9ng= =8qJy -----END PGP SIGNATURE-----