Date: Tue, 22 Sep 2020 13:37:14 +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 333 v3 (CVE-2020-25602) - x86 pv: Crash when handling guest access to MSR_MISC_ENABLE -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2020-25602 / XSA-333 version 3 x86 pv: Crash when handling guest access to MSR_MISC_ENABLE UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= When a guest accesses certain Model Specific Registers, Xen first reads the value from hardware to use as the basis for auditing the guest access. For the MISC_ENABLE MSR, which is an Intel specific MSR, this MSR read is performed without error handling for a #GP fault, which is the consequence of trying to read this MSR on non-Intel hardware. IMPACT ====== A buggy or malicious PV guest administrator can crash Xen, resulting in a host Denial of Service. VULNERABLE SYSTEMS ================== Only x86 systems are vulnerable. ARM systems are not vulnerable. Only Xen versions 4.11 and onwards are vulnerable. 4.10 and earlier are not vulnerable. Only x86 systems which do not implement the MISC_ENABLE MSR (0x1a0) are vulnerable. AMD and Hygon systems do not implement this MSR and are vulnerable. Intel systems do implement this MSR and are not vulnerable. Other manufacturers have not been checked. Only x86 PV guests can exploit the vulnerability. x86 HVM/PVH guests cannot exploit the vulnerability. MITIGATION ========== Running only HVM/PVH guests avoids the vulnerability. CREDITS ======= This issue was discovered by Andrew Cooper of Citrix. 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. xsa333.patch Xen 4.11 - xen-unstable $ sha256sum xsa333* 3f3d974ede9fe80f4eb63640dce058cf9e2073cd79e4c085c944f3ca5e454e26 xsa333.meta 8edec914fbdf036fba8cb54a75d3a9b025fac936e0af35512954a2dc2b12a26f xsa333.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/4UyVfoK9kFAl9p/eUMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZu5EH/RAaLJocX5UJfEZ4QT2osvnc1aaZjBXNz4JN1HDj 46pGxBOv1kEDxBu/lqbbXEY2aLeBLder2nj0OHCYgDkPCh4fqaciBqCEO97COqzo dFvN17dZ0pjyBUoSXs8mVPWjMblBjf6/Mt+/gh8speJQ32V3lHz6xYc9Nu0CVoL5 +RiaRVPGYOVndF5A0XK6UIiiMAOcVgPHpg485QFT2EIVPlKVu/jDrrsYep/9OrmP bamEjKcYoFBBsMlpUNAtUK0QZGnSAe2vVtbUNeHgY5T5BDuJzLZXdMDGmBDXK2vV 0PNMOoIeFev6Pq7yuvvTqI0PKEBmO825hkbZ5sEva/7pZ60= =zf3E -----END PGP SIGNATURE----- Download attachment "xsa333.meta" of type "application/octet-stream" (1301 bytes) Download attachment "xsa333.patch" of type "application/octet-stream" (1296 bytes)
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