nixos/tests: add tests for exercising various hardening features

This test exercises the linux_hardened kernel along with the various
hardening features (enabled via the hardened profile).

Move hidepid test from misc, so that misc can go back to testing a vanilla
configuration.

nixos/tests/hardened.nix

@@ -0,0 +1,31 @@
+import ./make-test.nix ({ pkgs, ...} : {
+  name = "hardened";
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ joachifm ];
+  };
+
+  machine =
+    { config, lib, pkgs, ... }:
+    with lib;
+    { users.users.alice = { isNormalUser = true; extraGroups = [ "proc" ]; };
+      users.users.sybil = { isNormalUser = true; group = "wheel"; };
+      imports = [ ../modules/profiles/hardened.nix ];
+    };
+
+  testScript =
+    ''
+      # Test hidepid
+      subtest "hidepid", sub {
+          $machine->succeed("grep -Fq hidepid=2 /proc/mounts");
+          $machine->succeed("[ `su - sybil -c 'pgrep -c -u root'` = 0 ]");
+          $machine->succeed("[ `su - alice -c 'pgrep -c -u root'` != 0 ]");
+      };
+
+      # Test kernel module hardening
+      subtest "lock-modules", sub {
+          $machine->waitForUnit("multi-user.target");
+          # note: this better a be module we normally wouldn't load ...
+          $machine->fail("modprobe dccp");
+      };
+    '';
+})