From: eLinux.org
This page has security information about bootloaders.
There are two methods of booting
TCG is a hardware-based security solution not only for the PC platform, but also applicable for embedded devices. To understand the TCG, TCG Specification Architecture Overview is a good document.
Using the Trusted Platform Module(TPM) security chip and write-protected boot-code, we will be able to implement the Trusted Boot efficiently. Unfortunately, Many existing TPMs are designed for PC Platform, it requires LPC bus. Thus you have to use glue logic to use such TPM with your system. But, Atmel(R) has been released TPM chip, AT97SC3201S which has I2C/SMBus interface.
Project site: u-boot
GRUB is a bootloader for PC Platform. There are two patches to enable the TCG's Trusted Boot.
(In this case, the BIOS must support TCG Trusted Boot)
GRUB provides a password feature, only administrator can start the interactive operations.
EtherBoot is a software package for creating ROM images that can download code over an Ethernet network to be executed on an x86 computer. "SafeBootMode means any NBI image that's downloaded is checked whether it contains a valid digital signature and if not, the user is notified."