Date: Tue, 21 Mar 2023 12:00:39 +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 427 v2 (CVE-2022-42332) - x86 shadow plus log-dirty mode use-after-free -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2022-42332 / XSA-427 version 2 x86 shadow plus log-dirty mode use-after-free UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= In environments where host assisted address translation is necessary but Hardware Assisted Paging (HAP) is unavailable, Xen will run guests in so called shadow mode. Shadow mode maintains a pool of memory used for both shadow page tables as well as auxiliary data structures. To migrate or snapshot guests, Xen additionally runs them in so called log-dirty mode. The data structures needed by the log-dirty tracking are part of aformentioned auxiliary data. In order to keep error handling efforts within reasonable bounds, for operations which may require memory allocations shadow mode logic ensures up front that enough memory is available for the worst case requirements. Unfortunately, while page table memory is properly accounted for on the code path requiring the potential establishing of new shadows, demands by the log-dirty infrastructure were not taken into consideration. As a result, just established shadow page tables could be freed again immediately, while other code is still accessing them on the assumption that they would remain allocated. IMPACT ====== Guests running in shadow mode and being subject to migration or snapshotting may be able to cause Denial of Service and other problems, including escalation of privilege. VULNERABLE SYSTEMS ================== All Xen versions from at least 3.2 onwards are vulnerable. Earlier versions have not been inspected. Only x86 systems are vulnerable. The vulnerability is limited to migration and snapshotting of guests, and only to PV ones as well as HVM or PVH ones run with shadow paging. MITIGATION ========== Not migrating or snapshotting guests will avoid the vulnerability. Running only HVM or PVH guests and only in HAP (Hardware Assisted Paging) mode will also avoid the vulnerability. CREDITS ======= This issue was discovered by Jan Beulich of SUSE. 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. xsa427.patch xen-unstable - Xen 4.17.x xsa427-4.16.patch Xen 4.16.x xsa427-4.15.patch Xen 4.15.x xsa427-4.14.patch Xen 4.14.x $ sha256sum xsa427* 5ebcdc495ba6f439e47be7e17dbb8fbdecf4de66d2fac560d460f6841bd3bef3 xsa427.meta aa39316cbb81478c62b3d5c5aea7edfb6ade3bc5e6d0aa8c4677f9ea7bcc97a2 xsa427.patch 5ba679bc2170b0d9cd4c6ce139057e3287a6ee00434fa0e9a7a02441420030ff xsa427-4.14.patch 410ee6be28412841ab5aba1131f7dd7b84b9983f6c93974605f196fd278562e1 xsa427-4.15.patch 76c1850eb9a274c1feb5a8645f61ecf394a0551278f4e40e123ec07ea307f101 xsa427-4.16.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/4UyVfoK9kFAmQZlVkMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZgRMH/RU6mB8M/feJeZDkYbrLPmT3yLiw6BpWroMTUTpv 5kIlixxlfQqyv8gqd25p5WMMKUsZlPZdLCT0iOlyMTNz6EUPRBME2Yb3ByiM7O7/ kFtlFDk5ZY5c/Vk1w0XuLm+YcABj0xnsn003YvgknmZfBJ2HWdR2iIayT/NjfQ+u twErqUqa7il2Em5M8ZwHZeJjCUN9t+g2sv5sdI/rQeRge8ofjsquLubpgUVMGjiV xwwUPCn3co0/2WArB4mHjWCNcoATk1NVZ3CTUyKGl5Mr+EvdmYWvzmlDa4wc8QPV tNoASqXw0MbOOTy+RnZQHwappCDP371MirPq4IaTwiXy7eo= =0flx -----END PGP SIGNATURE----- Download attachment "xsa427.meta" of type "application/octet-stream" (1316 bytes) Download attachment "xsa427.patch" of type "application/octet-stream" (3199 bytes) Download attachment "xsa427-4.14.patch" of type "application/octet-stream" (3621 bytes) Download attachment "xsa427-4.15.patch" of type "application/octet-stream" (3610 bytes) Download attachment "xsa427-4.16.patch" of type "application/octet-stream" (3152 bytes)
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