[ELSA-2019-2473] kernel security and bug fix update

[2.6.32-754.18.2.OL6]
- Update genkey [bug 25599697]

[2.6.32-754.18.2]
- [x86] x86/speculation: Enable Spectre v1 swapgs mitigations (Waiman Long) [1724512] {CVE-2019-1125}
- [x86] x86/speculation: Prepare entry code for Spectre v1 swapgs mitigations (Waiman Long) [1724512] {CVE-2019-1125}

[2.6.32-754.18.1]
- [virt] xenbus: don't look up transaction IDs for ordinary writes (Vitaly Kuznetsov) [1663262]
- [virt] xenbus: don't BUG() on user mode induced condition (Vitaly Kuznetsov) [1663262]
- [virt] xenbus: Add proper handling of XS_ERROR from Xenbus for transactions (Vitaly Kuznetsov) [1663262]
- [fs] proc: restrict kernel stack dumps to root (Denys Vlasenko) [1638193] {CVE-2018-17972}
- [crypto] salsa20 - fix blkcipher_walk API usage (Bruno Eduardo de Oliveira Meneguele) [1543984]
- [mm] vmscan: do not loop on too_many_isolated for ever (Rafael Aquini) [1658254]
- [x86] spec_ctrl: Don't report the use of retpoline on Skylake as vulnerable (Waiman Long) [1666102]
- [mm] try harder to allocate vmemmap blocks (Rafael Aquini) [1591394]
- [v4l] dvb: revert spectre v1 mitigation (Josh Poimboeuf) [1647975]
- [fs] binfmt_misc.c: do not allow offset overflow (Bill O'Donnell) [1710149]
- [x86] pti: Don't use PCID and INVPCID in x86-32 (Waiman Long) [1702782]
- [mm] mincore.c: make mincore() more conservative (Rafael Aquini) [1664197] {CVE-2019-5489}
- [x86] spec: Move retp_compiler() inline function to bugs.c (Waiman Long) [1722185]