From 0b59d379fc2f5833134195ba767297d8efd1e31f Mon Sep 17 00:00:00 2001 From: Daniel Axtens Date: Mon, 6 Oct 2025 12:55:03 +0530 Subject: [PATCH] docs/grub: Document signing GRUB under UEFI Before adding information about how GRUB is signed with an appended signature scheme, it's worth adding some information about how it can currently be signed for UEFI. Signed-off-by: Daniel Axtens Signed-off-by: Sudhakar Kuppusamy Reviewed-by: Stefan Berger Reviewed-by: Avnish Chouhan Reviewed-by: Daniel Kiper --- docs/grub.texi | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/docs/grub.texi b/docs/grub.texi index 1c33b44e2..b796b4796 100644 --- a/docs/grub.texi +++ b/docs/grub.texi @@ -8907,6 +8907,7 @@ environment variables and commands are listed in the same order. * Measured Boot:: Measuring boot components * Lockdown:: Lockdown when booting on a secure setup * TPM2 key protector:: Managing disk key with TPM2 key protector +* Signing GRUB itself:: Ensuring the integrity of the GRUB core image @end menu @node Authentication and authorisation @@ -8987,7 +8988,7 @@ commands. GRUB's @file{core.img} can optionally provide enforcement that all files subsequently read from disk are covered by a valid digital signature. -This document does @strong{not} cover how to ensure that your +This section does @strong{not} cover how to ensure that your platform's firmware (e.g., Coreboot) validates @file{core.img}. If environment variable @code{check_signatures} @@ -9595,6 +9596,21 @@ which increases the risk of password leakage during the process. Moreover, the superuser list must be well maintained, and the password used cannot be synchronized with LUKS key rotation. +@node Signing GRUB itself +@section Signing GRUB itself +To ensure a complete secure-boot chain, there must be a way for the code that +loads GRUB to verify the integrity of the core image. +This is ultimately platform-specific and individual platforms can define their +own mechanisms. However, there are general-purpose mechanisms that can be used +with GRUB. +@section Signing GRUB for UEFI secure boot +On UEFI platforms, @file{core.img} is a PE binary. Therefore, it can be signed +with a tool such as @command{pesign} or @command{sbsign}. Refer to the +suggestions in @pxref{UEFI secure boot and shim} to ensure that the final +image works under UEFI secure boot and can maintain the secure-boot chain. It +will also be necessary to enroll the public key used into a relevant firmware +key database. + @node Platform limitations @chapter Platform limitations -- 2.47.3