![]() In July, the security vulnerability, named “BootHole”, has drawn people’s attention. it is signed and verified by “db” but any one of certificates in a chain of trust is found in “dbx” or.it is signed and its signature is validated by one of the certificates in “dbx”.it is signed and its signature is validated by one of the certificates in “db” (there can be a number of intermediate certificates involved) or.“db” database may have x509 certificates, hashes of images as signatures and “dbx” may additionally contain hashes of certificates. There are four main signature databases used here. When attempting to load an image file, U-Boot checks for the image’s signature against signature databases to determine if the image is trusted or not. UEFI Secure Boot is based on message digests (hashes) and public key cryptography technologies. Instead, the basic logic under UEFI Secure Boot will be outlined here. Since there are a variety of articles about UEFI Secure Boot on websites, for example, we will not dive into technical details. It is not intended to supersede U-Boot original, it’s up to the user’s choice based on system requirements. On the other hand, UEFI Secure Boot provides a more flexible manner for key management in addition to compatibility with existing third party software (including linux distributions). There are always pro’s and con’s For example, the original secure boot can sign and verify not only binaries but also other type of data like device tree blob and initrd, and UEFI Secure Boot can only deal with PE (Portable Executable) executables (at least, for now). In fact, U-Boot already has its own secure boot framework, dubbed FIT Signature Verification. It is, as the name suggests, a security framework in boot sequence which is designed to protect the system from malware being executed by ensuring that only trusted software, EFI applications and OS kernels, are loaded and executed in the middle of transferring the control from the firmware to the OS. (At the time of writing, the status is in -rc5.) Secure Boot: How it works?Īmong others, UEFI Secure Boot is a new feature introduced in the latest U-Boot release, v2020.10. This allows us to evaluate to what extent the current implementation is compliant with the UEFI specification and has contributed to the enhancement in conformity. Furthermore, UEFI SCT (Self Certification Tests) can also be executed directly on U-Boot. While the primary target OS is linux, other OSs like BSD variants are also confirmed to work with UEFI U-Boot. There is still plenty of missing features and restrictions, but the functionality is now mature enough to run software like: a subset of relevant protocols (block devices, console, network etc.).a limited number of runtime services (after OS starts).most of boottime services (before OS starts).It defines a set of requirements that the firmware on embedded devices should follow to enable standard OSs installed without customization.Īt the time of writing this article, UEFI U-Boot provides : EBBR is a collective document being developed by the community. To further strengthen interoperability (and hence compatibility with the existing implementation like EDK-II), UEFI U-Boot now reinforces its development goal that it should fully commit and adhere to EBBR (Embedded Base Boot Requirement). It might be worth mentioning that, in the latest release, risc-v is added to a list of supported architectures along with arm and x86.) (At Linaro we focus on the arm ecosystem, but those developments benefit other architectures as well. Linaro participated in this community activity since 2018 and worked together to help improve the functionality as well as the quality. No distributions support it on arm64 or x86.Īccordingly, a huge amount of effort has been devoted on developing UEFI interfaces on top of U-Boot framework since 2016. Remember that grub can support U-Boot’s own APIs but only on arm port. While U-Boot is still popular among embedded world, supporting generic interfaces like UEFI will make it much easier for users to bring a wider range of OS distributions to their platforms with minimized efforts and no customization. It has been the default on PC and server side, so now is on arm64 platforms. UEFI (Unified Extensible Firmware Interface) is the specification developed by UEFI Forum to standardize interfaces between firmware and the OS’s, aiming to replace legacy BIOS on PC architecture. How does it work and what is it designed to protect you against? UEFI U-Boot In the last few years, a number of new UEFI interfaces have been brought into U-Boot, and the latest element added is Secure Boot. U-Boot is a favorite boot loader for embedded devices, supporting a variety of architectures and platforms.
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