By Wcoekaer-Oracle on Mar 13, 2015
Another feature introduced with Oracle Linux 7.1 is support for Secure Boot.
If Secure Boot is enabled on a system (typically desktop, but in some cases also servers) - the system can have an embedded certificate (in firmware). This certificate can be one that's uploaded to the system by the admin or it could be one provided by the OEM/OS vendor. In many cases, in particular newer desktops, the system already contains the Microsoft key. (there can be more than one certificate uploaded...). When the firmware loads the boot loader, it verifies/checks the signature of this bootloader with the key stored in firmware before continuing. This signed bootloader (at this point trusted to continue) will then load a signed kernel, or signed second stage boot loader and verify it before starting and continuing the boot process. This creates what is called a chain of trust through the boot process.
We ship a 1st stage bootloader with Oracle Linux 7.1 which is a tiny "shim" layer that is signed by both Microsoft and Oracle. So if a system comes with Secure Boot support, and already ships the microsoft PK, then the shim layer will be started, verified, and if it passes verification, it will then load grub2 (the real bootloader). grub2 is signed by us (Oracle). The signed/verified shim layer contains the Oracle key and will validate that grub2 is ours (signed), if verification passes, grub2 will load the Oracle Linux kernel, and the same process takes place, our kernel is signed by us (Oracle) and grub2 will validate the signature prior to allowing execution of the kernel. Once the kernel is running, all kernel modules that we ship as part of Oracle Linux whether it's standard included kernel modules as part of the kernel RPM or external kernel modules used with Oracle Ksplice, are also signed by Oracle and the kernel will validate the signature prior to loading these kernel modules.
Enabling loading and verification of signed kernel modules is done by adding enforcemodulesig=1 to the grub kernel option line. In enforcing mode, any kernel module that is attempted to be loaded that's not signed by Oracle will fail to load.
If a system has Secure Boot support but a sysadmin wants to use the Oracle signature instead, we will make our certificate available to be downloaded securely from Oracle and then this can be uploaded into the firmware key database.