From 41997d49dae6aec5b29a14b6e9b850835f52d911 Mon Sep 17 00:00:00 2001
From: Oliver Schmidt <os@flyingcircus.io>
Date: Mon, 23 Feb 2026 17:13:40 +0100
Subject: [PATCH] nixos/grub: re-install grub on package change

Trigger re-installation of grub files when the store path of the grub
package changes.
This is consistent with how side-effects are executed in other parts of
NixOS, e.g. systemd service management, and ensures that the actually
running grub stays in sync with the grub package in the Nix store that
is part of the system closure.
In particular, this causes security patches or dependency changes to be
taken into effect without the need to bump the package version.

Impact:
This change causes a re-installation of grub for all systems,
due to the lack of a persisted grub store path in existing state files.

Background:
So far we only re-installed grub outside of the store when its its
version, the package name, or some flags changed.
This leads to the various security patches only fixing new installations
of grub and not existing ones. This has been like this for over a decade,
but it remains unclear why the implementation decision had been to
be overly cautious with modifying boot loader side effects.

Fixes #486315

PL-135147
---
 .../system/boot/loader/grub/install-grub.pl   | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/nixos/modules/system/boot/loader/grub/install-grub.pl b/nixos/modules/system/boot/loader/grub/install-grub.pl
index f5ae844da21f..f61c91f02db8 100644
--- a/nixos/modules/system/boot/loader/grub/install-grub.pl
+++ b/nixos/modules/system/boot/loader/grub/install-grub.pl
@@ -685,12 +685,14 @@ struct(GrubState => {
     efi => '$',
     devices => '$',
     efiMountPoint => '$',
+    grub => '$',
+    grubEfi => '$',
     extraGrubInstallArgs => '@',
 });
 # If you add something to the state file, only add it to the end
 # because it is read line-by-line.
 sub readGrubState {
-    my $defaultGrubState = GrubState->new(name => "", version => "", efi => "", devices => "", efiMountPoint => "", extraGrubInstallArgs => () );
+    my $defaultGrubState = GrubState->new(name => "", version => "", efi => "", devices => "", efiMountPoint => "", grub => "", grubEfi => "", extraGrubInstallArgs => () );
     open my $fh, "<", "$bootPath/grub/state" or return $defaultGrubState;
     local $/ = "\n";
     my $name = <$fh>;
@@ -721,8 +723,10 @@ sub readGrubState {
     }
     my %jsonState = %{decode_json($jsonStateLine)};
     my @extraGrubInstallArgs = exists($jsonState{'extraGrubInstallArgs'}) ? @{$jsonState{'extraGrubInstallArgs'}} : ();
+    my $grubValue = exists($jsonState{'grub'}) ? $jsonState{'grub'} : "";
+    my $grubEfiValue = exists($jsonState{'grubEfi'}) ? $jsonState{'grubEfi'} : "";
     close $fh;
-    my $grubState = GrubState->new(name => $name, version => $version, efi => $efi, devices => $devices, efiMountPoint => $efiMountPoint, extraGrubInstallArgs => \@extraGrubInstallArgs );
+    my $grubState = GrubState->new(name => $name, version => $version, efi => $efi, devices => $devices, efiMountPoint => $efiMountPoint, extraGrubInstallArgs => \@extraGrubInstallArgs, grub => $grubValue, grubEfi => $grubEfiValue );
     return $grubState
 }
 
@@ -734,15 +738,16 @@ my @prevExtraGrubInstallArgs = @{$prevGrubState->extraGrubInstallArgs};
 
 my $devicesDiffer = scalar (List::Compare->new( '-u', '-a', \@deviceTargets, \@prevDeviceTargets)->get_symmetric_difference());
 my $extraGrubInstallArgsDiffer = scalar (List::Compare->new( '-u', '-a', \@extraGrubInstallArgs, \@prevExtraGrubInstallArgs)->get_symmetric_difference());
-my $nameDiffer = get("fullName") ne $prevGrubState->name;
-my $versionDiffer = get("fullVersion") ne $prevGrubState->version;
 my $efiDiffer = $efiTarget ne $prevGrubState->efi;
 my $efiMountPointDiffer = $efiSysMountPoint ne $prevGrubState->efiMountPoint;
+# re-installing grub once the package store path changes is necessary, because
+# introducing patches or adjusting builds does not always bump the version number
+my $grubStorePathsDiffer = ($grub ne $prevGrubState->grub) || ($grubEfi ne $prevGrubState->grubEfi);
 if (($ENV{'NIXOS_INSTALL_GRUB'} // "") eq "1") {
     warn "NIXOS_INSTALL_GRUB env var deprecated, use NIXOS_INSTALL_BOOTLOADER";
     $ENV{'NIXOS_INSTALL_BOOTLOADER'} = "1";
 }
-my $requireNewInstall = $devicesDiffer || $extraGrubInstallArgsDiffer || $nameDiffer || $versionDiffer || $efiDiffer || $efiMountPointDiffer || (($ENV{'NIXOS_INSTALL_BOOTLOADER'} // "") eq "1");
+my $requireNewInstall = $devicesDiffer || $extraGrubInstallArgsDiffer || $efiDiffer || $efiMountPointDiffer || $grubStorePathsDiffer || (($ENV{'NIXOS_INSTALL_BOOTLOADER'} // "") eq "1");
 
 # install a symlink so that grub can detect the boot drive
 my $tmpDir = File::Temp::tempdir(CLEANUP => 1) or die "Failed to create temporary space: $!";
@@ -795,7 +800,9 @@ if ($requireNewInstall != 0) {
     print $fh join( ",", @deviceTargets ), "\n" or die;
     print $fh $efiSysMountPoint, "\n" or die;
     my %jsonState = (
-        extraGrubInstallArgs => \@extraGrubInstallArgs
+        extraGrubInstallArgs => \@extraGrubInstallArgs,
+        grub => $grub,
+        grubEfi => $grubEfi
     );
     my $jsonStateLine = encode_json(\%jsonState);
     print $fh $jsonStateLine, "\n" or die;