diff --git a/nixos/modules/image/assert_uki_repart_match.py b/nixos/modules/image/assert_uki_repart_match.py new file mode 100644 index 000000000000..e0f266cf15bf --- /dev/null +++ b/nixos/modules/image/assert_uki_repart_match.py @@ -0,0 +1,78 @@ +import json +import sys + +store_verity_type = "@NIX_STORE_VERITY@" # replaced at import by Nix + + +def extract_uki_cmdline_params(ukify_json: dict) -> dict[str, str]: + """ + Return a dict of the parameters in the .cmdline section of the UKI + Exits early if "usrhash" is not included. + """ + cmdline = ukify_json.get(".cmdline", {}).get("text") + if cmdline is None: + print("Failed to get cmdline from ukify output") + + params = {} + for param in cmdline.split(): + key, val = param.partition("=")[::2] + params[key] = val + + if "usrhash" not in params: + print( + f"UKI cmdline does not contain a usrhash:\n{cmdline}" + ) + exit(1) + + return params + + +def hashes_match(partition: dict[str, str], expected: str) -> bool: + """ + Checks if the value of the "roothash" key in the passed partition object matches `expected`. + """ + if partition.get("roothash") != expected: + pretty_part = json.dumps(partition, indent=2) + print( + f"hash mismatch, expected to find roothash {expected} in:\n{pretty_part}" + ) + return False + else: + return True + + +def check_partitions( + partitions: list[dict], uki_params: dict[str, str] +) -> bool: + """ + Checks if the usrhash from `uki_params` has a matching roothash + for the corresponding partition in `partitions`. + """ + for part in partitions: + if part.get("type") == store_verity_type: + expected = uki_params["usrhash"] + return hashes_match(part, expected) + + return False + + +def main() -> None: + ukify_json = json.load(sys.stdin) + repart_json_output = sys.argv[1] + + with open(repart_json_output, "r") as r: + repart_json = json.load(r) + + uki_params = extract_uki_cmdline_params(ukify_json) + + if check_partitions(repart_json, uki_params): + print("UKI and repart verity hashes match") + else: + print("Compatibility check for UKI and image failed!") + print(f"UKI cmdline parameters:\n{uki_params}") + print(f"repart config: {repart_json_output}") + exit(1) + + +if __name__ == "__main__": + main() diff --git a/nixos/modules/image/repart-verity-store.nix b/nixos/modules/image/repart-verity-store.nix new file mode 100644 index 000000000000..3f341ca421f2 --- /dev/null +++ b/nixos/modules/image/repart-verity-store.nix @@ -0,0 +1,209 @@ +# opinionated module that can be used to build nixos images with +# a dm-verity protected nix store +{ + config, + pkgs, + lib, + ... +}: +let + cfg = config.image.repart.verityStore; + + verityMatchKey = "store"; + + # TODO: make these and other arch mappings available from systemd-lib for example + partitionTypes = { + usr = + { + "x86_64" = "usr-x86-64"; + "arm64" = "usr-arm64"; + } + ."${pkgs.stdenv.hostPlatform.linuxArch}"; + + usr-verity = + { + "x86_64" = "usr-x86-64-verity"; + "arm64" = "usr-arm64-verity"; + } + ."${pkgs.stdenv.hostPlatform.linuxArch}"; + }; + + verityHashCheck = + pkgs.buildPackages.writers.writePython3Bin "assert_uki_repart_match.py" + { + flakeIgnore = [ "E501" ]; # ignores PEP8's line length limit of 79 (black defaults to 88 characters) + } + ( + builtins.replaceStrings [ "@NIX_STORE_VERITY@" ] [ + partitionTypes.usr-verity + ] (builtins.readFile ./assert_uki_repart_match.py) + ); +in +{ + options.image.repart.verityStore = { + enable = lib.mkEnableOption "building images with a dm-verity protected nix store"; + + ukiPath = lib.mkOption { + type = lib.types.str; + default = "/EFI/Linux/${config.system.boot.loader.ukiFile}"; + defaultText = "/EFI/Linux/\${config.system.boot.loader.ukiFile}"; + description = '' + Specify the location on the ESP where the UKI is placed. + ''; + }; + + partitionIds = { + esp = lib.mkOption { + type = lib.types.str; + default = "00-esp"; + description = '' + Specify the attribute name of the ESP. + ''; + }; + store-verity = lib.mkOption { + type = lib.types.str; + default = "10-store-verity"; + description = '' + Specify the attribute name of the store's dm-verity hash partition. + ''; + }; + store = lib.mkOption { + type = lib.types.str; + default = "20-store"; + description = '' + Specify the attribute name of the store partition. + ''; + }; + }; + }; + + config = lib.mkIf cfg.enable { + boot.initrd.systemd.dmVerity.enable = true; + + image.repart.partitions = { + # dm-verity hash partition + ${cfg.partitionIds.store-verity}.repartConfig = { + Type = partitionTypes.usr-verity; + Verity = "hash"; + VerityMatchKey = lib.mkDefault verityMatchKey; + Label = lib.mkDefault "store-verity"; + }; + # dm-verity data partition that contains the nix store + ${cfg.partitionIds.store} = { + storePaths = [ config.system.build.toplevel ]; + repartConfig = { + Type = partitionTypes.usr; + Verity = "data"; + Format = lib.mkDefault "erofs"; + VerityMatchKey = lib.mkDefault verityMatchKey; + Label = lib.mkDefault "store"; + }; + }; + + }; + + system.build = { + + # intermediate system image without ESP + intermediateImage = + (config.system.build.image.override { + # always disable compression for the intermediate image + compression.enable = false; + }).overrideAttrs + ( + _: previousAttrs: { + # make it easier to identify the intermediate image in build logs + pname = "${previousAttrs.pname}-intermediate"; + + # do not prepare the ESP, this is done in the final image + systemdRepartFlags = previousAttrs.systemdRepartFlags ++ [ "--defer-partitions=esp" ]; + + # the image will be self-contained so we can drop references + # to the closure that was used to build it + unsafeDiscardReferences.out = true; + } + ); + + # UKI with embedded usrhash from intermediateImage + uki = + let + inherit (config.system.boot.loader) ukiFile; + cmdline = "init=${config.system.build.toplevel}/init ${toString config.boot.kernelParams}"; + in + # override the default UKI + lib.mkOverride 99 ( + pkgs.runCommand ukiFile + { + nativeBuildInputs = [ + pkgs.jq + pkgs.systemdUkify + ]; + } + '' + mkdir -p $out + + # Extract the usrhash from the output of the systemd-repart invocation for the intermediate image. + usrhash=$(jq -r \ + '.[] | select(.type=="${partitionTypes.usr-verity}") | .roothash' \ + ${config.system.build.intermediateImage}/repart-output.json + ) + + # Build UKI with the embedded usrhash. + ukify build \ + --config=${config.boot.uki.configFile} \ + --cmdline="${cmdline} usrhash=$usrhash" \ + --output="$out/${ukiFile}" + '' + ); + + # final system image that is created from the intermediate image by injecting the UKI from above + finalImage = + (config.system.build.image.override { + # continue building with existing intermediate image + createEmpty = false; + }).overrideAttrs + ( + finalAttrs: previousAttrs: + let + copyUki = "CopyFiles=${config.system.build.uki}/${config.system.boot.loader.ukiFile}:${cfg.ukiPath}"; + in + { + nativeBuildInputs = previousAttrs.nativeBuildInputs ++ [ + pkgs.systemdUkify + verityHashCheck + ]; + + postPatch = '' + # add entry to inject UKI into ESP + echo '${copyUki}' >> $finalRepartDefinitions/${cfg.partitionIds.esp}.conf + ''; + + preBuild = '' + # check that we build the final image with the same intermediate image for + # which the injected UKI was built by comparing the UKI cmdline with the repart output + # of the intermediate image + # + # This is necessary to notice incompatible substitutions of + # non-reproducible store paths, for example when working with distributed + # builds, or when offline-signing the UKI. + ukify --json=short inspect ${config.system.build.uki}/${config.system.boot.loader.ukiFile} \ + | assert_uki_repart_match.py "${config.system.build.intermediateImage}/repart-output.json" + + # copy the uncompressed intermediate image, so that systemd-repart picks it up + cp -v ${config.system.build.intermediateImage}/${config.image.repart.imageFileBasename}.raw . + chmod +w ${config.image.repart.imageFileBasename}.raw + ''; + + # the image will be self-contained so we can drop references + # to the closure that was used to build it + unsafeDiscardReferences.out = true; + } + ); + }; + }; + + meta.maintainers = with lib.maintainers; [ + nikstur + willibutz + ]; +} diff --git a/nixos/modules/image/repart.nix b/nixos/modules/image/repart.nix index e471f9485cd0..b2f03d96ad35 100644 --- a/nixos/modules/image/repart.nix +++ b/nixos/modules/image/repart.nix @@ -69,6 +69,10 @@ let }) opts; in { + imports = [ + ./repart-verity-store.nix + ]; + options.image.repart = { name = lib.mkOption {