rhboot/shim: UEFI shim loader ·
shim is a trivial EFI application that, when run, attempts to open and execute another application. It will initially attempt to do this via the standard EFI LoadImage() and StartImage() calls. If these fail (because Secure Boot is enabled and the binary is not signed with an appropriate key, for instance) it will then validate the binary against a built-in certificate. If this succeeds and if the binary or signing key are not forbidden then shim will relocate and execute the binary. shim will also install a protocol which permits the second-stage bootloader to perform similar binary validation. This protocol has a GUID as described in the shim.h header file and provides a single entry point. On 64-bit systems this entry point expects to be called with SysV ABI rather than MSABI, so calls to it should not be wrapped. Since version 16.1 shim overrides the system table and installs its own version of the LoadImage()/StartImage()/UnloadImage()/Exit() functions, so that second stages can s