![]() None of us had ever seen the secure boot enable flag or the BIOS password stored anywhere except inside of an NVRAM variable. We could have just found the file responsible for showing the setup screen to the user and patched out the password check, but that wasn't possible on this laptop because hardware-based firmware security was enabled. The BIOS region consists of several firmware filesystem volumes and an NVRAM variable storage area. However the only region that we cared about was the BIOS region. Intel flash images are divided into several regions. The flash's contents were formatted as an Intel image and could readily be parsed by UEFITool We quickly identified the flash chip on our laptop's motherboard, and promptly attached it to a SPI flash programmer with some clips. The flash chip is usually the chip with the bulkiest package on the board. Flash Black Magic Dumping the FlashĪt heart, PCs are just large, powerful, embedded devices-and like most embedded devices they have flash chips that we can dump and rewrite. Nested volumes are commonly used to support volume compression. A file can also be a container for another volume, which enables nested volumes (i.e. Files are identified by a GUID rather than by a name, although some file types define a way to optionally provide a name. A flash image will contain one or more firmware volumes, and each volume will contain one or more firmware files. UEFI defines its own filesystem format for use in flash images. Some of these drivers persist even after your OS has booted. The DXE phase contains all of the drivers and applications that run before your OS boots, including your OS's bootloader. After verification, the PEI phase switches the CPU into 64-bit mode and starts the DXE phase. ![]() The PEI phase configures some non-CPU platform components and optionally verifies the integrity of the DXE phase's code. The PCH verifies the firmware for the SEC and PEI phases before the CPU begins executing any code. In þe days of olde the SEC phase also acted as the root of trust for the system, but nowadays that role is assigned to the PCH. This mode switch marks the end of the SEC phase and the beginning of the PEI phase. ![]() The SEC phase configures a minimal set of CPU registers and then switches the CPU into 32-bit mode.
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