Date: Wed, 13 Feb 2013 16:50:41 +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@....org> Subject: Xen Security Advisory 42 (CVE-2013-0228) - Linux kernel hits general protection if %ds is corrupt for 32-bit PVOPS. -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2013-0228 / XSA-42 version 2 Linux kernel hits general protection if %ds is corrupt for 32-bit PVOPS. UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= Linux kernel when returning from an iret assumes that %ds segment is safe and uses it to reference various per-cpu related fields. Unfortunately the user can modify the LDT and provide a NULL one. Whenever an iret is called we end up in xen_iret and try to use the %ds segment and cause an general protection fault. IMPACT ====== Malicious or buggy unprivileged user space can cause the guest kernel to crash, or permit a privilege escalation within the guest, or operate erroneously. VULNERABLE SYSTEMS ================== All 32bit PVOPS versions of Linux are affected, since the introduction of Xen PVOPS support in 2.6.23. Classic-Xen kernels are not vulnerable. MITIGATION ========== This can be mitigated by not running 32bit PVOPS Linux guests. 32bit classic-Xen guests, all 64bit PV guests and all HVM guests are unaffected. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. $ sha256sum xsa42*.patch a931fdc161653fb1a3a6d8c1cf6d2c9954c5aec134b610be6e9699552a659eb8 xsa42-pvops-0001-x86-xen-don-t-assume-ds-is-usable-in-xen_iret-for-32.patch $ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBAgAGBQJRG8PxAAoJEIP+FMlX6CvZC3gH/0v/9nr3jXbsMHZlkBRtCx9n np1ed8btQGpmmk/WqbyLj/KcTNlXLIa1zwhTSPUgXlVIoDPuzstfGXm96gBNfYhS hl56QYTruhHPAvvrAwE8SNIlMUH+n7Wq1BThkXFU1yBnjXxzTi4SdmUwy4gAA/SE Xp35RAcIV6IwLRMMY12aat7XKnVx4S5n+gCC5eu0WZ+n73Ecrlqmsq+2X2ZHo3wP nu9UN+PChmBJHfcA8OhelY/X4X4DV1HNPuFkj9ypyPrvXIrl6M0D5TfGoyRNXMHq izAn51ro8gTGND6xY+s3auelquKiJkyl/5AXnfd0y9bSewGJS6oxoRzFdctJqxM= =mgHb -----END PGP SIGNATURE----- Download attachment "xsa42-pvops-0001-x86-xen-don-t-assume-ds-is-usable-in-xen_iret-for-32.patch" of type "application/octet-stream" (4959 bytes)
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