nixos/stage-1: check secret paths before copying

Fixes #84976.

nixos/modules/system/boot/stage-1.nix

@@ -137,6 +137,8 @@ let
       ''}
 
       # Copy secrets if needed.
+      #
+      # TODO: move out to a separate script; see #85000.
       ${optionalString (!config.boot.loader.supportsInitrdSecrets)
           (concatStringsSep "\n" (mapAttrsToList (dest: source:
              let source' = if source == null then dest else source; in
@@ -579,6 +581,25 @@ in
         message = "boot.resumeDevice has to be an absolute path."
           + " Old \"x:y\" style is no longer supported.";
       }
+      # TODO: remove when #85000 is fixed
+      { assertion = !config.boot.loader.supportsInitrdSecrets ->
+          all (source:
+            builtins.isPath source ||
+            (builtins.isString source && hasPrefix source builtins.storeDir))
+          (attrValues config.boot.initrd.secrets);
+        message = ''
+          boot.loader.initrd.secrets values must be unquoted paths when
+          using a bootloader that doesn't natively support initrd
+          secrets, e.g.:
+
+            boot.initrd.secrets = {
+              "/etc/secret" = /path/to/secret;
+            };
+
+          Note that this will result in all secrets being stored
+          world-readable in the Nix store!
+        '';
+      }
     ];
 
     system.build =