Date: Tue, 26 Jul 2022 19:24:16 +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 408 v3 (CVE-2022-33745) - insufficient TLB flush for x86 PV guests in shadow mode -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2022-33745 / XSA-408 version 3 insufficient TLB flush for x86 PV guests in shadow mode UPDATES IN VERSION 3 ==================== Update hash for metadata file. ISSUE DESCRIPTION ================= For migration as well as to work around kernels unaware of L1TF (see XSA-273), PV guests may be run in shadow paging mode. To address XSA-401, code was moved inside a function in Xen. This code movement missed a variable changing meaning / value between old and new code positions. The now wrong use of the variable did lead to a wrong TLB flush condition, omitting flushes where such are necessary. IMPACT ====== The known (observed) impact would be a Denial of Service (DoS) affecting the entire host, due to running out of memory. Privilege escalation and information leaks cannot be ruled out. VULNERABLE SYSTEMS ================== All versions of Xen with the XSA-401 fixes applied are vulnerable. Only x86 PV guests can trigger this vulnerability, and only when running in shadow mode. Shadow mode would be in use when migrating guests or as a workaround for XSA-273 (L1TF). MITIGATION ========== Not running x86 PV guests will avoid the vulnerability. CREDITS ======= This issue was discovered by Charles Arnold 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. xsa408.patch xen-unstable - Xen 4.14.x xsa408-4.13.patch Xen 4.13.x $ sha256sum xsa408* 9411b563c71445d2c95e36aba9d71fa3b9341f0230e4b3e2549a63292df11669 xsa408.meta f49cb67842c7576f1d59b965331956a9fa1f529a8e2da3531d7ebc4eb3f079b3 xsa408.patch 26871efbd3f834dd4af4fbab6f2cb09a83c509e49894f025ee656071419ed995 xsa408-4.13.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/4UyVfoK9kFAmLgPzsMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZT5cIAKtisZZvdcSolZ+RHFzAdVEP2lbEW2TyoG6oy0st kMsV/ZSabthow9PiUp48DoZOXSIh/7hn2qyXqx5X0VYjiWOISVRCldm5g4p0+tA/ GN6FztbRR1GargLkvtuWj38K9E7HIqfBRFLbtJD6X97NFSAPeNNZg8nqQPqwkhK+ yeGBjPPO5pTjNwsRt91A1qEttTPjbBpipEcit/qjqqCBxX6NT/pYSE5Ltn2OHm38 eYM25X901rJl0rPsyOeUN312FAL0bEunKVKJbiNcHVBZoR37YoJ5HE5trDxoxPrz XYJdR7gzcB028lbGU4jt9FVHdYCh0htWpdpdWci4A3DCH7U= =C02g -----END PGP SIGNATURE----- Download attachment "xsa408.meta" of type "application/octet-stream" (1306 bytes) Download attachment "xsa408.patch" of type "application/octet-stream" (1633 bytes) Download attachment "xsa408-4.13.patch" of type "application/octet-stream" (1525 bytes)
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