sbsigntool - Signing utility for UEFI secure boot
Copyright (C) 2102 Jeremy Kerr [email protected]
Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.
See file ./INSTALL for building and installation instructions.
Main git repository: git:https://kernel.ubuntu.com/jk/sbsigntool.git
sbsigntool is free software. See the file COPYING for copying conditions.
This is a fork of sbsigntools to fix issues preventing the use of the tools -- particularly sbsign -- with Amazon's CloudHSM, and likely other HSMs:
- sbsigntools intentionally does not allow the use of dynamic engines. This eliminates the risk that a malicous engine will be loaded. Solution: Accept the risk and change the code to allow dynamic engines.
- sbsigntools assumes keys are in an engine form when an engine is specified. This does not work for HSMs that use a safety key design -- where a "fake" key is stored in a file outside of the HSM, and this key is mapped to the real key in the HSM for cryptographic operations performed by the HSM. Solution: Add a new optional switch to specify the keyform and add PEM for use with safety keys and an engine.
- sbsigntools does not initialize OpenSSL engines with all methods, which prevents HSMs that use a safety key from mapping the key. Solution: Alter the code to initialize OpenSSL engines with all methods.
- sbsigntools loads an OpenSSL engine right before loading a key, then immediately closes the engine. Thus, the engine is not available for mapping when the key is used. Solution: Alter the code to ensure an engine specified on the command line is available throughout a tool's execution.
To sign a Linux kernel using a key stored in AWS CloudHSM:
A. Generate a PKI suitable for UEFI code signing as usual using the openssl commands, but be sure to add the switch: -engine cloudhsm
B. Specify the new switch --keyform that this fork adds when using sbsign: sbsign --engine cloudhsm --key <keyfile> --keyform PEM --cert <cert> <kernelfile>