It was found that espfix funcionality (when returning to userspace with a 16
bit stack, the CPU will not restore the high word(s) of stack pointer for us
on executing iret and thus potentially leaks kernel addresses; espfix fixes
this) can be bypassed by installing 16-bit RW data segment into GDT instead
of LDT (which espfix checks for) and using it for stack.
A local unprivileged user could potentially use this flaw to leak kernel
Red Hat would like to thank Andy Lutomirski for reporting this issue.
This issue did not affect the Linux kernel packages as shipped with Red
Hat Enterprise Linux 7 and Red Hat Enterprise Linux MRG 2.
Red Hat Enterprise Linux 5 is now in Production 3 Phase of the support and
maintenance life cycle. This has been rated as having Low security
impact and is not currently planned to be addressed in future updates. For
additional information, refer to the Red Hat Enterprise Linux Life
Created kernel tracking bugs for this issue:
Affects: fedora-all [bug 1174374]
kernel-3.17.7-200.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.
kernel-3.17.7-300.fc21 has been pushed to the Fedora 21 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