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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.
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 ...
UEFI systems can utilize legacy Option ROMs through the Compatibility Support Module (CSM). When Secure Boot is enabled, the execution of CSM and legacy Option ROMs is prohibited as legacy firmware drivers do not support authentication, which creates a potential security vulnerability. [7] [8]
Note: The column MBR (Master Boot Record) refers to whether or not the boot loader can be stored in the first sector of a mass storage device. The column VBR (Volume Boot Record) refers to the ability of the boot loader to be stored in the first sector of any partition on a mass storage device.
The UEFI (not legacy boot via CSM) does not rely on boot sectors, UEFI system loads the boot loader (EFI application file in USB disk or in the EFI system partition) directly. [1] Additionally, the UEFI specification also contains "secure boot", which basically wants the UEFI code to be digitally signed.
The Primary Bootloader (PBL), which is stored in the Boot ROM [3] is the first stage of the boot process. This code is written by the chipset manufacturer. [4] The PBL verifies the authenticity of the next stage. On Samsung smartphones, the Samsung Secure Boot Key (SSBK) is used by the boot ROM to verify the next stages. [5]
Whole disk: Whether the whole physical disk or logical volume can be encrypted, including the partition tables and master boot record. Note that this does not imply that the encrypted disk can be used as the boot disk itself; refer to pre-boot authentication in the features comparison table.
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 ...