The Linux kernel before 5.4.1 on powerpc allows Information Exposure because the Spectre-RSB mitigation is not in place for all applicable CPUs, aka CID-39e72bf96f58. This is related to arch/powerpc/kernel/entry_64.S and arch/powerpc/kernel/security.c.
https://www.openwall.com/lists/oss-security/2019/11/27/1
https://usn.ubuntu.com/4228-2/
https://usn.ubuntu.com/4228-1/
https://usn.ubuntu.com/4227-2/
https://usn.ubuntu.com/4227-1/
https://usn.ubuntu.com/4226-1/
https://usn.ubuntu.com/4225-2/
https://usn.ubuntu.com/4225-1/
https://security.netapp.com/advisory/ntap-20200103-0001/
https://seclists.org/bugtraq/2020/Jan/10
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.4.1
https://access.redhat.com/errata/RHSA-2020:0174
http://www.openwall.com/lists/oss-security/2019/11/27/1
http://lists.opensuse.org/opensuse-security-announce/2019-12/msg00029.html