Date: Tue, 15 Dec 2020 12:20:29 +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 359 v3 (CVE-2020-29571) - FIFO event channels control structure ordering -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2020-29571 / XSA-359 version 3 FIFO event channels control structure ordering UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= A bounds check common to most operation time functions specific to FIFO event channels depends on the CPU observing consistent state. While the producer side uses appropriately ordered writes, the consumer side isn't protected against re-ordered reads, and may hence end up de-referencing a NULL pointer. IMPACT ====== Malicious or buggy guest kernels can mount a Denial of Service (DoS) attack affecting the entire system. VULNERABLE SYSTEMS ================== All Xen versions from 4.4 onwards are vulnerable. Xen versions 4.3 and earlier are not vulnerable. Only Arm systems may be vulnerable. Whether a system is vulnerable will depend on the specific CPU. x86 systems are not vulnerable. MITIGATION ========== There is no known mitigation. CREDITS ======= This issue was discovered by Julien Grall of Amazon. RESOLUTION ========== Applying the 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. xsa359.patch xen-unstable - 4.10 $ sha256sum xsa359* cb009ad77d1a3d8044431b2af568dd9dffefe07fc9f537fb6b53c2ec57aa77b7 xsa359.meta 3126d9304b68be84a89c42c223227c8f96ecbb96a0385a7e1bdc65ae5e0f344f xsa359.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/4UyVfoK9kFAl/YqeAMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZt6wIAJhvfVB8eRr5fqCbMUjZ++KKoG0AF/hoS7YRHiDn zCgK/ff5RkY/pHHkVnrSOQeQg88SPBp/HaYljUXhoANbhXVxlt383QxQb63JwanR 1c3Sdvv5w0HdvrDyUMV16W/Edf/DGlSgciG/2saNz8pPbqiGKzeY3Q7nj3T3vLAE ouNlHb2NItalKB2AdC62y/BFIjsn66G/P1agxyrcGirJxdvzORBx+LY7VTFOrOEB L7yb8Y0U6Nj1XjGUXYm4X4xCCm+940Xc0Ht9zkDJlb3xSdO5sOtBE+Cx3F4uXn1c vTMiKziAOgEKKXWV7P3KSWR/7G1aTm2YVRMy5XWtS6GY5D0= =uRRE -----END PGP SIGNATURE----- Download attachment "xsa359.meta" of type "application/octet-stream" (2724 bytes) Download attachment "xsa359.patch" of type "application/octet-stream" (1245 bytes)
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