Date: Wed, 25 Apr 2018 12:03:36 +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 259 - x86: PV guest may crash Xen with XPTI -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory XSA-259 version 2 x86: PV guest may crash Xen with XPTI UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= The workaround for the Meltdown vulnerability (XSA-254) failed to deal with an error code path connecting the INT 80 handling with general exception handling. This results in an unconditional write attempt of the value zero to an address near 2^64, in cases where a PV guest has no handler installed for INT 80 on one of its vCPU-s. IMPACT ====== A malicious or buggy guest may cause a hypervisor crash, resulting in a Denial of Service (DoS) affecting the entire host. VULNERABLE SYSTEMS ================== All Xen versions which the XSA-254 fixes were applied to are vulnerable. Only x86 systems are vulnerable. ARM systems are not vulnerable. Only x86 PV guests can exploit the vulnerability. x86 PVH and HVM guests cannot exploit the vulnerability. MITIGATION ========== Running only PVH or HVM guests avoids the vulnerability. CREDITS ======= This issue was discovered by Andrew Cooper of Citrix. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa259.patch xen-unstable, Xen 4.10.x ... xen 4.7.x xsa259-4.6.patch Xen 4.6.x $ sha256sum xsa259* 5c14a90af066c952974324b361e2a428c280f876b854f0c85a78e8579054a4d1 xsa259.meta ff2efb5eb2502ded988d0aa15351030a15494a9e2223eafbb88377a8e4d39dcb xsa259.patch c40bc8802077cf73f8393fb50574b7c7efbc4d127e202b0ebd757d34aa07aac3 xsa259-4.6.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----- Version: GnuPG v1 iQEcBAEBCAAGBQJa4G58AAoJEIP+FMlX6CvZrqIH+QFfC5NOoFhVZAChTU0WQ7U6 UwP7yEyLeY15VrGb4YvwzKhvTNwsRRiYTbTNB/QjAkrUkMRhBiUIz7mQqBl0Vc/N 4zblt+YNdDMjhCllTjvtYU6OJzbsqvEBByB4mFrz6fxfZiuXIbOnMUOxLHRRdXLR 6JR8+4RrheKNl9DF6lmLj50d3G/fKrNLY9id8VcDG1TGIB6E1CbJ6gibw7FiYDSq PETa5O1szo2FO2yY+xcMzzGLHv+oVeKZnmuq9KYtP7Q+G823Twz1RE6rTBEjwhs9 sDGUlgZ48QVfSzer10syzyeX0p9hLHyKhlJnCrmCiywvKq68/uVexZFNcOKRPtE= =n+01 -----END PGP SIGNATURE----- Download attachment "xsa259.meta" of type "application/octet-stream" (1700 bytes) Download attachment "xsa259.patch" of type "application/octet-stream" (1225 bytes) Download attachment "xsa259-4.6.patch" of type "application/octet-stream" (1283 bytes)
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