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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2022.0375 Xen Security Advisory CVE-2022-23034 27 January 2022 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Xen Publisher: Xen Operating System: Xen Impact/Access: Denial of Service -- Existing Account Resolution: Patch/Upgrade CVE Names: CVE-2022-23034 Original Bulletin: http://xenbits.xen.org/xsa/advisory-394.html - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2022-23034 / XSA-394 version 3 A PV guest could DoS Xen while unmapping a grant UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= To address XSA-380, reference counting was introduced for grant mappings for the case where a PV guest would have the IOMMU enabled. PV guests can request two forms of mappings. When both are in use for any individual mapping, unmapping of such a mapping can be requested in two steps. The reference count for such a mapping would then mistakenly be decremented twice. Underflow of the counters gets detected, resulting in the triggering of a hypervisor bug check. IMPACT ====== Malicious guest kernels may be able to mount a Denial of Service (DoS) attack affecting the entire system. VULNERABLE SYSTEMS ================== All Xen versions from at least 3.2 onwards are vulnerable in principle, if they have the XSA-380 fixes applied. Only x86 systems are vulnerable. Arm systems are not vulnerable. Only x86 PV guests with access to PCI devices can leverage the vulnerability. x86 HVM and PVH guests, as well as PV guests without access to PCI devices, cannot leverage the vulnerability. Additionally from Xen 4.13 onwards x86 PV guests can leverage this vulnerability only when being granted access to pages owned by another domain. MITIGATION ========== Not running PV guests will avoid the vulnerability. For Xen 4.12 and older not passing through PCI devices to PV guests will avoid the vulnerability. For Xen 4.13 and newer not enabling PCI device pass-through for PV guests will avoid the vulnerability. This can be achieved via omitting any "passthrough=..." and "pci=..." settings from xl guest configuration files, or by setting "passthrough=disabled" there. - - From Xen 4.13 onwards, XSM SILO can be available as a security policy designed to permit guests to only be able to communicate with Dom0. Dom0 does not normally offer its pages for guests to map, which means the use of SILO mode normally mitigates the vulnerability. CREDITS ======= This issue was discovered by Julien Grall of Amazon. 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. xsa394.patch xen-unstable - Xen 4.13.x xsa394-4.12.patch Xen 4.12.x $ sha256sum xsa394* 93f4d3b58d49ba239115753c9905b7c3720b438c48ef8fb701f15081aa317159 xsa394.meta f2a3420e8d3eb1cf728f90d3c352ace0d3c67f7933201ce9b784d63afaeaa179 xsa394.patch ee93797546ac9e82f98211366f9acc733332b0d5ab7ef73840c2acd2bb1439ca xsa394-4.12.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches described above (or others which are substantially similar) is permitted during the embargo, even on public- facing systems with untrusted guest users and administrators. HOWEVER, deployment of the mitigations described above is NOT permitted during the embargo on public-facing systems with untrusted guest users and administrators. This is because such a configuration change is recognizable by the affected guests. AND: 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/4UyVfoK9kFAmHv39IMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZfCYH/iZn73/JRTKI7B+9v2fW6v/k1IcVhpu+N4+TuRhh Al5igmiTJLU3LcHM/H2KScgtnSwEKfCyddY1Gt3MZ+5lBDwR8elRkPdqn+P7xfol 4D5NgnEJDAYUWwJZOFn0qWfqNDnDkAvuKpm1zmv8RE0Xmw6a74Fvbfvi8PCuN9CO zdippi5r5FlzFU7Q5MoWmOhmvVe3Fg7tGs4GXIyVUYkpDYyBGEWBo6rcoQ5aDvir g8T0P1Y8XKCVvYM9SOdKWENppam0uIh00Mm+QDjQNaXD4I3DCDXLXkT7OGImZglr MW8z5iNFjd0iXxFqTVBe1omxUhLC1xcB1fNySjd3zpt3RfA= =mIA+ - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. 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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 iQIVAwUBYfIvB+NLKJtyKPYoAQhrlw//f5e39LiHzRuD6IeqRpDM8co96tLZ1Yzg 9peHquBll9OjQYDilJoHszfMYj8PAEfVpgWZEw+ikCXCkzRoLEk/8M1ZgmgqXwU2 ZZ9aimqxUsHXO2ifBehJEDwRomKxRR0tpUCRT/fjlFXtnCG3nbrZw311/vO6WsQ8 3hCCYtw5ciDboGzhkn+NiDzrQ0T9cTLODxEdiIhaAgYh8Le53npvXpdXNSFVK2vi xorQyLJGnC31wyacXer+4Bu8i0LME5fRzJQujIX6Nv9cB5Pj4B+i50/sYT+xkCPc LjejJDNJ+qNMlBLJU9q4avBKFanXYdbS7vkwyJf9OeHyFE/wvxh8aBgITVLjEDiD dixpf7vTllZ3E/9kvd4Ce5K9e0NpRrodZ542KX820RtZHPGj3UVtMVRCjFVIK60X zrtEVCmOIGZusLyiY5+KQY6n5MPrtyueJ7u0NRuL61Uieutac14IN5xWrnMpcPde FQ/XC6aExgm9/tmbm0SENlkMA8vPpeJTb0C4jQmBkF/GS+V5aekARbNo4Dl6UjND NZrAC8EQE0THouzhbb8xot9XUu8J9NHF34mpM0XHnGkFv8Tr46rZU/0+p3nMnqfW CDiKaZ3ybNE55/idU+OLaz6ZWsi75Td9VqUxlAVrK8c8V1XzRoqh/jNYp8u+vsAJ y5lFlmGRp+c= =Co+l -----END PGP SIGNATURE-----