A vulnerability was found in the RHEL7.2 kernel. When RHEL 7.2 is booted with UEFI Secure Boot enabled, securelevel is set. The kernel uses the state of securelevel to prevent userspace from inserting untrusted privileged code at runtime.

The ACPI tables provided by firmware can be overwritten using the initrd. From the kernel documentation:

If the ACPIINITRDTABLEOVERRIDE compile option is true, it is possible to override nearly any ACPI table provided by the BIOS with an instrumented, modified one.

RHEL 7.2 has CONFIGACPIINITRDTABLEOVERRIDE kernel config option enabled, and will load ACPI tables appended to the initrd, even if booted with UEFI Secure Boot enabled and securelevel set.

Upstream patch:

https://github.com/mjg59/linux/commit/a4a5ed2835e8ea042868b7401dced3f517cafa76