It was found that the Linux kernel KVM subsystem's sysenter instruction emulation was not sufficient. An unprivileged guest user could use this flaw to escalate their privileges by tricking the hypervisor to emulate a SYSENTER instruction in 16-bit mode, if the guest OS does not initialize the SYSENTER MSRs. Please note that the Red Hat Enterprise Linux with KVM certified guest operating systems do initialize the SYSENTER MSRs and are thus not vulnerable to this issue when running on KVM hypervisor. References: http://www.openwall.com/lists/oss-security/2015/01/27/6 Upstream patch: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f3747379accba8e95d70cec0eae0582c8c182050 Acknowledgements: Red Hat would like to thank Nadav Amit for reporting this issue.
Created kernel tracking bugs for this issue: Affects: fedora-all [bug 1186453]
Statement: This issue did not affect the kvm packages as shipped with Red Hat Enterprise Linux 5 as they lack support for sysenter instruction emulation. This issue affects the Linux kernel packages as shipped with Red Hat Enterprise Linux 7. A future update may address this issue. Please note that the Red Hat Enterprise Linux with KVM certified guest operating systems do initialize the SYSENTER MSRs and are thus not vulnerable to this issue when running on KVM hypervisor.
kernel-3.18.5-201.fc21 has been pushed to the Fedora 21 stable repository. If problems still persist, please make note of it in this bug report.
kernel-3.18.5-101.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.
This issue has been addressed in the following products: Red Hat Enterprise Linux 6 Via RHSA-2015:1272 https://rhn.redhat.com/errata/RHSA-2015-1272.html
This issue has been addressed in the following products: Red Hat Enterprise Linux 7 Via RHSA-2015:2152 https://rhn.redhat.com/errata/RHSA-2015-2152.html