Date: Wed, 15 Aug 2018 16:09:51 +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 274 v3 (CVE-2018-14678) - Linux: Uninitialized state in x86 PV failsafe callback path -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2018-14678 / XSA-274 version 3 Linux: Uninitialized state in x86 PV failsafe callback path UPDATES IN VERSION 3 ==================== Fix spelling in CREDITS. ISSUE DESCRIPTION ================= Linux has a `failsafe` callback, invoked by Xen under certain conditions. Normally in this failsafe callback, error_entry is paired with error_exit; and error_entry uses %ebx to communicate to error_exit whether to use the user or kernel return path. Unfortunately, on 64-bit PV Xen on x86, error_exit is called without error_entry being called first, leaving %ebx with an invalid value. IMPACT ====== A rogue user-space program could crash a guest kernel. Privilege escalation cannot be ruled out. VULNERABLE SYSTEMS ================== Only 64-bit x86 PV Linux systems are vulnerable. All versions of Linux are vulnerable. MITIGATION ========== Switching to HVM or PVH guests will mitigate this issue. CREDITS ======= This issue was discovered by M. Vefa Bicakci, and recognized as a security issue by Andy Lutomirski. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. NB this patch has not been accepted into Linux upstream yet. An updated advisory will be sent if the fix upstreamed looks significantly different. xsa274-linux-4.17.patch Linux 4.17 $ sha256sum xsa274* 0c30cb13d1d573f446c8cb8d4824ffad8ef9149a7589a19ef9bcc83c07bddcf5 xsa274-linux-4.17.patch $ NOTE ON THE LACK OF EMBARGO =========================== The patch for this issue was published on linux-kernel without being first reported to the XenProject Security Team. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBCAAGBQJbdFA5AAoJEIP+FMlX6CvZWQQIAIxMK2w6CsH2aNQRDiDrgcBc 2FkBbroS5I1XHEhWVyO19aPhp1R3mYNU+pTUUFOevQuKvTP0nuZ0csgk5LUj9UP7 EE/3vM3jkAfmIIuXCAegOcznnEl6Wi9aMKGVXcxMkRu9qjKStGr4We5qvmdPncUj DkTdD6VbmM/Q665b0jU4j2aZPDMsH63qrsbz1rsnPAlYUi1R+yKw56Q5UdRJK17j Jc74v+elyqOkFq7QwH1usfnko+DQziLyLqEBQOztTSps2qYM+VwHLAZkhxNyuLsu 2x9/1D8XoZ+BHvVsVe50QmoNcJViMMunnHNhWYHmtXLYFErwUOt48N1vl+3xFpo= =k4Ak -----END PGP SIGNATURE----- Download attachment "xsa274-linux-4.17.patch" of type "application/octet-stream" (4131 bytes)
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