Merge pull request #209156 from pwaller/issue-114594

nixos/grub: Name initrd-secrets by system, not by initrd

nixos/modules/system/boot/loader/grub/install-grub.pl

@@ -450,8 +450,9 @@ sub addEntry {
 
     # Include second initrd with secrets
     if (-e -x "$path/append-initrd-secrets") {
-        my $initrdName = basename($initrd);
-        my $initrdSecretsPath = "$bootPath/kernels/$initrdName-secrets";
+        # Name the initrd secrets after the system from which they're derived.
+        my $systemName = basename(Cwd::abs_path("$path"));
+        my $initrdSecretsPath = "$bootPath/kernels/$systemName-secrets";
 
         mkpath(dirname($initrdSecretsPath), 0, 0755);
         my $oldUmask = umask;
@@ -470,7 +471,7 @@ sub addEntry {
         if (-e $initrdSecretsPathTemp && ! -z _) {
             rename $initrdSecretsPathTemp, $initrdSecretsPath or die "failed to move initrd secrets into place: $!\n";
             $copied{$initrdSecretsPath} = 1;
-            $initrd .= " " . ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/kernels/$initrdName-secrets";
+            $initrd .= " " . ($grubBoot->path eq "/" ? "" : $grubBoot->path) . "/kernels/$systemName-secrets";
         } else {
             unlink $initrdSecretsPathTemp;
             rmdir dirname($initrdSecretsPathTemp);

nixos/modules/virtualisation/qemu-vm.nix

@@ -152,9 +152,11 @@ let
 
       ${lib.optionalString cfg.useBootLoader
       ''
-        # Create a writable copy/snapshot of the boot disk.
-        # A writable boot disk can be booted from automatically.
-        ${qemu}/bin/qemu-img create -f qcow2 -F qcow2 -b ${bootDisk}/disk.img "$TMPDIR/disk.img"
+        if ${if !cfg.persistBootDevice then "true" else "! test -e $TMPDIR/disk.img"}; then
+          # Create a writable copy/snapshot of the boot disk.
+          # A writable boot disk can be booted from automatically.
+          ${qemu}/bin/qemu-img create -f qcow2 -F qcow2 -b ${bootDisk}/disk.img "$TMPDIR/disk.img"
+        fi
 
         NIX_EFI_VARS=$(readlink -f "''${NIX_EFI_VARS:-${cfg.efiVars}}")
 
@@ -370,6 +372,17 @@ in
           '';
       };
 
+    virtualisation.persistBootDevice =
+      mkOption {
+        type = types.bool;
+        default = false;
+        description =
+          lib.mdDoc ''
+            If useBootLoader is specified, whether to recreate the boot device
+            on each instantiaton or allow it to persist.
+            '';
+      };
+
     virtualisation.emptyDiskImages =
       mkOption {
         type = types.listOf types.ints.positive;
@@ -853,6 +866,8 @@ in
     # * The disks are attached in `virtualisation.qemu.drives`.
     #   Their order makes them appear as devices `a`, `b`, etc.
     # * `fileSystems."/boot"` is adjusted to be on device `b`.
+    # * The disk.img is recreated each time the VM is booted unless
+    #   virtualisation.persistBootDevice is set.
 
     # If `useBootLoader`, GRUB goes to the second disk, see
     # note [Disk layout with `useBootLoader`].

nixos/tests/all-tests.nix

@@ -311,6 +311,7 @@ in {
   initrd-network-ssh = handleTest ./initrd-network-ssh {};
   initrdNetwork = handleTest ./initrd-network.nix {};
   initrd-secrets = handleTest ./initrd-secrets.nix {};
+  initrd-secrets-changing = handleTest ./initrd-secrets-changing.nix {};
   input-remapper = handleTest ./input-remapper.nix {};
   inspircd = handleTest ./inspircd.nix {};
   installer = handleTest ./installer.nix {};

nixos/tests/initrd-secrets-changing.nix

@@ -0,0 +1,58 @@
+{ system ? builtins.currentSystem
+, config ? {}
+, pkgs ? import ../.. { inherit system config; }
+, lib ? pkgs.lib
+, testing ? import ../lib/testing-python.nix { inherit system pkgs; }
+}:
+
+let
+  secret1InStore = pkgs.writeText "topsecret" "iamasecret1";
+  secret2InStore = pkgs.writeText "topsecret" "iamasecret2";
+in
+
+testing.makeTest {
+  name = "initrd-secrets-changing";
+
+  nodes.machine = { ... }: {
+    virtualisation.useBootLoader = true;
+    virtualisation.persistBootDevice = true;
+
+    boot.loader.grub.device = "/dev/vda";
+
+    boot.initrd.secrets = {
+      "/test" = secret1InStore;
+      "/run/keys/test" = secret1InStore;
+    };
+    boot.initrd.postMountCommands = "cp /test /mnt-root/secret-from-initramfs";
+
+    specialisation.secrets2System.configuration = {
+      boot.initrd.secrets = lib.mkForce {
+        "/test" = secret2InStore;
+        "/run/keys/test" = secret2InStore;
+      };
+    };
+  };
+
+  testScript = ''
+    start_all()
+
+    machine.wait_for_unit("multi-user.target")
+    print(machine.succeed("cat /run/keys/test"))
+    machine.succeed(
+        "cmp ${secret1InStore} /secret-from-initramfs",
+        "cmp ${secret1InStore} /run/keys/test",
+    )
+    # Select the second boot entry corresponding to the specialisation secrets2System.
+    machine.succeed("grub-reboot 1")
+    machine.shutdown()
+
+    with subtest("Check that the specialisation's secrets are distinct despite identical kernels"):
+        machine.wait_for_unit("multi-user.target")
+        print(machine.succeed("cat /run/keys/test"))
+        machine.succeed(
+            "cmp ${secret2InStore} /secret-from-initramfs",
+            "cmp ${secret2InStore} /run/keys/test",
+        )
+        machine.shutdown()
+  '';
+}