On 10/2/25 8:31 AM, Sudhakar Kuppusamy wrote:
From: Daniel Axtens <[email protected]>
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 <[email protected]>
Signed-off-by: Sudhakar Kuppusamy <[email protected]>
Reviewed-by: Stefan Berger <[email protected]>
Reviewed-by: Avnish Chouhan <[email protected]>
Reviewed-by: Daniel Kiper <[email protected]>
---
docs/grub.texi | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/docs/grub.texi b/docs/grub.texi
index 8a23c29a3..358975fc8 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
Again,
Reviewed-by: Stefan Berger <[email protected]>
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