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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Sat, 15 Aug 2020 02:00:57 +1000
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Subject: [PATCH] docs/grub: Document signing grub under UEFI
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Before adding information about how grub is signed with an appended
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signature scheme, it's worth adding some information about how it
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can currently be signed for UEFI.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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---
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docs/grub.texi | 22 +++++++++++++++++++++-
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1 file changed, 21 insertions(+), 1 deletion(-)
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diff --git a/docs/grub.texi b/docs/grub.texi
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index 4870faaa00a..365d1d6931b 100644
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--- a/docs/grub.texi
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+++ b/docs/grub.texi
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@@ -5817,6 +5817,7 @@ environment variables and commands are listed in the same order.
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* Secure Boot Advanced Targeting:: Embedded information for generation number based revocation
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* Measured Boot:: Measuring boot components
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* Lockdown:: Lockdown when booting on a secure setup
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+* Signing GRUB itself:: Ensuring the integrity of the GRUB core image
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@end menu
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@node Authentication and authorisation
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@@ -5895,7 +5896,7 @@ commands.
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GRUB's @file{core.img} can optionally provide enforcement that all files
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subsequently read from disk are covered by a valid digital signature.
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-This document does @strong{not} cover how to ensure that your
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+This section does @strong{not} cover how to ensure that your
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platform's firmware (e.g., Coreboot) validates @file{core.img}.
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If environment variable @code{check_signatures}
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@@ -6067,6 +6068,25 @@ be restricted and some operations/commands cannot be executed.
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The @samp{lockdown} variable is set to @samp{y} when the GRUB is locked down.
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Otherwise it does not exit.
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+@node Signing GRUB itself
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+@section Signing GRUB itself
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+
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+To ensure a complete secure-boot chain, there must be a way for the code that
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+loads GRUB to verify the integrity of the core image.
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+
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+This is ultimately platform-specific and individual platforms can define their
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+own mechanisms. However, there are general-purpose mechanisms that can be used
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+with GRUB.
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+
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+@section Signing GRUB for UEFI secure boot
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+
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+On UEFI platforms, @file{core.img} is a PE binary. Therefore, it can be signed
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+with a tool such as @command{pesign} or @command{sbsign}. Refer to the
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+suggestions in @pxref{UEFI secure boot and shim} to ensure that the final
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+image works under UEFI secure boot and can maintain the secure-boot chain. It
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+will also be necessary to enrol the public key used into a relevant firmware
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+key database.
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+
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@node Platform limitations
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@chapter Platform limitations
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