nixos/config/swap: improve randomEncrytion

* add sector size parameter to swap randomEncryption
  * add key size parameter to swap randomEncryption
  * allow deviceName to be overridden for encrypted swap
  * create test for swap random encryption
  * update release notes

nixos/doc/manual/release-notes/rl-2305.section.md

@@ -363,6 +363,26 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - `nextcloud` has an option to enable SSE-C in S3.
 
+- NixOS swap partitions with random encryption can now control the sector size, cipher, and key size used to setup the plain encryption device over the
+  underlying block device rather than allowing them to be determined by `cryptsetup(8)`. One can use these features like so:
+
+  ```nix
+  {
+    swapDevices = [
+      {
+        device = "/dev/disk/by-partlabel/swapspace";
+
+        randomEncryption = {
+          enable = true;
+          cipher = "aes-xts-plain64";
+          keySize = 512;
+          sectorSize = 4096;
+        };
+      }
+    ];
+  }
+  ```
+
 - `services.peertube` now requires you to specify the secret file `secrets.secretsFile`. It can be generated by running `openssl rand -hex 32`.
   Before upgrading, read the release notes for PeerTube:
     - [Release v5.0.0](https://github.com/Chocobozzz/PeerTube/releases/tag/v5.0.0)

nixos/modules/config/swap.nix

@@ -38,6 +38,34 @@ let
         '';
       };
 
+      keySize = mkOption {
+        default = null;
+        example = "512";
+        type = types.nullOr types.int;
+        description = lib.mdDoc ''
+          Set the encryption key size for the plain device.
+
+          If not specified, the amount of data to read from `source` will be
+          determined by cryptsetup.
+
+          See `cryptsetup-open(8)` for details.
+        '';
+      };
+
+      sectorSize = mkOption {
+        default = null;
+        example = "4096";
+        type = types.nullOr types.int;
+        description = lib.mdDoc ''
+          Set the sector size for the plain encrypted device type.
+
+          If not specified, the default sector size is determined from the
+          underlying block device.
+
+          See `cryptsetup-open(8)` for details.
+        '';
+      };
+
       source = mkOption {
         default = "/dev/urandom";
         example = "/dev/random";
@@ -157,11 +185,11 @@ let
 
     };
 
-    config = rec {
+    config = {
       device = mkIf options.label.isDefined
         "/dev/disk/by-label/${config.label}";
       deviceName = lib.replaceStrings ["\\"] [""] (escapeSystemdPath config.device);
-      realDevice = if config.randomEncryption.enable then "/dev/mapper/${deviceName}" else config.device;
+      realDevice = if config.randomEncryption.enable then "/dev/mapper/${config.deviceName}" else config.device;
     };
 
   };
@@ -247,7 +275,12 @@ in
                 ''}
                 ${optionalString sw.randomEncryption.enable ''
                   cryptsetup plainOpen -c ${sw.randomEncryption.cipher} -d ${sw.randomEncryption.source} \
-                    ${optionalString sw.randomEncryption.allowDiscards "--allow-discards"} ${sw.device} ${sw.deviceName}
+                '' + concatLines (filter (s: s != "") [
+                    (optionalString (sw.randomEncryption.sectorSize != null) "--sector-size=${toString sw.randomEncryption.sectorSize} \\")
+                    (optionalString (sw.randomEncryption.keySize != null) "--key-size=${toString sw.randomEncryption.keySize} \\")
+                    (optionalString sw.randomEncryption.allowDiscards "--allow-discards \\")
+                  ]) + ''
+                    ${sw.device} ${sw.deviceName}
                   mkswap ${sw.realDevice}
                 ''}
               '';

nixos/tests/all-tests.nix

@@ -667,6 +667,7 @@ in {
   sudo = handleTest ./sudo.nix {};
   swap-file-btrfs = handleTest ./swap-file-btrfs.nix {};
   swap-partition = handleTest ./swap-partition.nix {};
+  swap-random-encryption = handleTest ./swap-random-encryption.nix {};
   sway = handleTest ./sway.nix {};
   switchTest = handleTest ./switch-test.nix {};
   sympa = handleTest ./sympa.nix {};

nixos/tests/swap-random-encryption.nix

@@ -0,0 +1,80 @@
+import ./make-test-python.nix ({ lib, pkgs, ... }:
+{
+  name = "swap-random-encryption";
+
+  nodes.machine =
+    { config, pkgs, lib, ... }:
+    {
+      environment.systemPackages = [ pkgs.cryptsetup ];
+
+      virtualisation.useDefaultFilesystems = false;
+
+      virtualisation.rootDevice = "/dev/vda1";
+
+      boot.initrd.postDeviceCommands = ''
+        if ! test -b /dev/vda1; then
+          ${pkgs.parted}/bin/parted --script /dev/vda -- mklabel msdos
+          ${pkgs.parted}/bin/parted --script /dev/vda -- mkpart primary 1MiB -250MiB
+          ${pkgs.parted}/bin/parted --script /dev/vda -- mkpart primary -250MiB 100%
+          sync
+        fi
+
+        FSTYPE=$(blkid -o value -s TYPE /dev/vda1 || true)
+        if test -z "$FSTYPE"; then
+          ${pkgs.e2fsprogs}/bin/mke2fs -t ext4 -L root /dev/vda1
+        fi
+      '';
+
+      virtualisation.fileSystems = {
+        "/" = {
+          device = "/dev/disk/by-label/root";
+          fsType = "ext4";
+        };
+      };
+
+      swapDevices = [
+        {
+          device = "/dev/vda2";
+
+          randomEncryption = {
+            enable = true;
+            cipher = "aes-xts-plain64";
+            keySize = 512;
+            sectorSize = 4096;
+          };
+        }
+      ];
+    };
+
+  testScript = ''
+    machine.wait_for_unit("multi-user.target")
+
+    with subtest("Swap is active"):
+      # Doesn't matter if the numbers reported by `free` are slightly off due to unit conversions.
+      machine.succeed("free -h | grep -E 'Swap:\s+2[45][0-9]Mi'")
+
+    with subtest("Swap device has 4k sector size"):
+      import json
+      result = json.loads(machine.succeed("lsblk -Jo PHY-SEC,LOG-SEC /dev/mapper/dev-vda2"))
+      block_devices = result["blockdevices"]
+      if len(block_devices) != 1:
+        raise Exception ("lsblk output did not report exactly one block device")
+
+      swapDevice = block_devices[0];
+      if not (swapDevice["phy-sec"] == 4096 and swapDevice["log-sec"] == 4096):
+        raise Exception ("swap device does not have the sector size specified in the configuration")
+
+    with subtest("Swap encrypt has assigned cipher and keysize"):
+      import re
+
+      results = machine.succeed("cryptsetup status dev-vda2").splitlines()
+
+      cipher_pattern = re.compile(r"\s*cipher:\s+aes-xts-plain64\s*")
+      if not any(cipher_pattern.fullmatch(line) for line in results):
+        raise Exception ("swap device encryption does not use the cipher specified in the configuration")
+
+      key_size_pattern = re.compile(r"\s*keysize:\s+512\s+bits\s*")
+      if not any(key_size_pattern.fullmatch(line) for line in results):
+        raise Exception ("swap device encryption does not use the key size specified in the configuration")
+  '';
+})