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When Secure Boot is enabled, it is initially placed in "setup" mode, which allows a public key known as the "platform key" (PK) to be written to the firmware. Once the key is written, Secure Boot enters "User" mode, where only UEFI drivers and OS boot loaders signed with the platform key can be loaded by the firmware.
Prior to the development and ubiquitous adoption of the Plug and Play BIOS standard, an add-on device such as a hard disk controller or a network adapter card (NIC) was generally required to include an option ROM in order to be bootable, as the motherboard BIOS did not include any support for the device and so could not incorporate it into the BIOS's boot protocol.
According to an AMD developer's guide, the subsystem is "responsible for creating, monitoring and maintaining the security environment" and "its functions include managing the boot process, initializing various security related mechanisms, and monitoring the system for any suspicious activity or events and implementing an appropriate response". [2]
A PBA environment serves as an extension of the BIOS, UEFI or boot firmware and guarantees a secure, tamper-proof environment external to the operating system as a trusted authentication layer. [2] The PBA prevents any operating system from loading until the user has confirmed he/she has the correct password to unlock the computer. [2]
If UEFI Secure Boot is supported, a "shim" or "Preloader" is often booted by the UEFI before the bootloader or EFI-stub-bearing kernel. [11] Even if UEFI Secure Boot is disabled this may be present and booted in case it is later enabled. It merely acts to add an extra signing key database providing keys for signature verification of subsequent ...
When GRUB is installed on a hard disk, boot.img is written into the boot sector of that hard disk. boot.img has a size of only 446 bytes. A boot sector is the sector of a persistent data storage device (e.g., hard disk , floppy disk , optical disc , etc.) which contains machine code to be loaded into random-access memory (RAM) and then executed ...
BIOS interrupt calls perform hardware control or I/O functions requested by a program, return system information to the program, or do both. A key element of the purpose of BIOS calls is abstraction - the BIOS calls perform generally defined functions, and the specific details of how those functions are executed on the particular hardware of the system are encapsulated in the BIOS and hidden ...
When a system on a chip (SoC) enters suspend to RAM mode, in many cases, the processor is completely off while the RAM is put in self refresh mode. At resume, the boot ROM is executed again and many boot ROMs are able to detect that the SoC was in suspend to RAM and can resume by jumping directly to the kernel which then takes care of powering on again the peripherals which were off and ...