Date: Tue, 08 Jan 2019 16:44:16 +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 279 v3 (CVE-2018-19965) - x86: DoS from attempting to use INVPCID with a non-canonical addresses -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2018-19965 / XSA-279 version 3 x86: DoS from attempting to use INVPCID with a non-canonical addresses UPDATES IN VERSION 3 ==================== CVE assigned. ISSUE DESCRIPTION ================= The INVPCID instruction raises #GP if an attempt is made to invalidate a non-canonical address. Older flushing mechanisms such as INVLPG tolerate this without error, and perform no action. There is one guest accessible path in Xen where a non-canonical address was passed into the TLB flushing code. This previously had no ill effect, but became vulnerable with the introduction of PCID to reduce the performance hit from the Meltdown mitigations. IMPACT ====== A buggy or malicious PV guest can crash the host. VULNERABLE SYSTEMS ================== Only hardware which supports the INVPCID instruction is vulnerable. This is available on Intel Haswell processors and later. AMD x86 processors are not known to support this instruction, and ARM processors are entirely unaffected. Only versions of Xen with PCID support are vulnerable. Support first appeared in Xen 4.11 but was backported to the stable trees as part of the Meltdown (XSA-254 / CVE-2017-5754) fixes. Xen 4.10.2, 4.9.3, 4.8.4 as well as the stable-4.7 and 4.6 branches are vulnerable. The vulnerability is only exposed to 64-bit PV guests. 32-bit PV guests, as well as HVM/PVH guests cannot exploit the vulnerability. MITIGATION ========== Booting Xen with `pcid=0` or `invpcid=0` on the command line will work around the issue. Alternatively, running untrusted 64bit PV guests inside xen-shim will work around the issue. CREDITS ======= This issue was discovered by Matthew Daley. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa279.patch xen-unstable, Xen 4.11.x, Xen 4.10.x xsa279-4.9.patch Xen 4.9.x ... 4.7.x $ sha256sum xsa279* 40319fcf33348176eb14d7fc7c68c255cc7291013242ea444de6d00602024a11 xsa279.meta 0c1d50effe6645051a15dd83af57088dd4a055e26a23b1fa9e6c3722a7973f5d xsa279.patch fd34f29bc7e53359585135408cbbd12e12a003f59b135e81cc44186c5cddd40d xsa279-4.9.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/4UyVfoK9kFAlw00zAMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZn0EH/0hSD6EUH7AyxFOCgPtaeOiRG0NPmGcnsVcHogU2 ows3sG+6+VenzyMdf0FcEqSEnCfFbQgqGuMaKE4U4ngSWWg+hdUhJ/5T/rMQv7o1 QJ84xhKRRHrAju1WZWdACZJpq7vAOiJmkS9HvkxjFw8J2ck+8KakyInLA1AlHC+K 8cApZtqxEyCNvH9w1Ho3PNtcNGhI6ZNxYlSSSUIfLz+dI7EXGQer2FiPzwE/KdAi vp0+61HotZ3mz03AZOelzJK7tmP5a8/u+zZfwfEw9s6zEO1RadUCHM3FIiZrSJLk v4si1s8x+FdbYwaHBKQGQTl6IQD/URqiK2IdWYdbeTkVCKY= =COoK -----END PGP SIGNATURE----- Download attachment "xsa279.meta" of type "application/octet-stream" (1778 bytes) Download attachment "xsa279.patch" of type "application/octet-stream" (1286 bytes) Download attachment "xsa279-4.9.patch" of type "application/octet-stream" (1203 bytes)
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