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nixpkgs/nixos/modules/services/hardware/tcsd.nix
rnhmjoj 538312709e
nixos/tcsd: several improvements and fixes
- Actually run tcsd as tss/tss
- Install a udev rule to set /dev/tpm* permissions
- Remove systemd-udev-settle dependency, use dev-tpm0.device instead
- Use systemd-tmpfiles to set up the state directory
- Add documentation URI to tcsd.service

This module cannot be easily tested with a NixOS test due to the TPM
dependency. Technically, one could be emulated using swtpm[1], but this
is not packaged in Nixpkgs. If you computer has a real TPM you can do a
passthrough in Qemu, but this requires running the VM as root and of
course it's not determinstic:

    $ nix build -f nixos vm --arg configuration '
      {
        virtualisation.qemu.options = [
          "-tpmdev passthrough,id=tpm0,path=/dev/tpm0,cancel-path=/sys/class/tpm/tpm0/cancel"
          "-device tpm-tis,tpmdev=tpm0"
        ];
        users.users.root.hashedPassword = "";
        services.tcsd.enable = true;
      }'

After starting the VM, log in as root, you can check the service has
started with `systemctl status tcsd`.

[1]: https://github.com/stefanberger/swtpm
2021-02-28 19:54:19 +01:00

161 lines
4.6 KiB
Nix

# tcsd daemon.
{ config, pkgs, lib, ... }:
with lib;
let
cfg = config.services.tcsd;
tcsdConf = pkgs.writeText "tcsd.conf" ''
port = 30003
num_threads = 10
system_ps_file = ${cfg.stateDir}/system.data
# This is the log of each individual measurement done by the system.
# By re-calculating the PCR registers based on this information, even
# finer details about the measured environment can be inferred than
# what is available directly from the PCR registers.
firmware_log_file = /sys/kernel/security/tpm0/binary_bios_measurements
kernel_log_file = /sys/kernel/security/ima/binary_runtime_measurements
firmware_pcrs = ${cfg.firmwarePCRs}
kernel_pcrs = ${cfg.kernelPCRs}
platform_cred = ${cfg.platformCred}
conformance_cred = ${cfg.conformanceCred}
endorsement_cred = ${cfg.endorsementCred}
#remote_ops = create_key,random
#host_platform_class = server_12
#all_platform_classes = pc_11,pc_12,mobile_12
'';
in
{
###### interface
options = {
services.tcsd = {
enable = mkOption {
default = false;
type = types.bool;
description = ''
Whether to enable tcsd, a Trusted Computing management service
that provides TCG Software Stack (TSS). The tcsd daemon is
the only portal to the Trusted Platform Module (TPM), a hardware
chip on the motherboard.
'';
};
user = mkOption {
default = "tss";
type = types.str;
description = "User account under which tcsd runs.";
};
group = mkOption {
default = "tss";
type = types.str;
description = "Group account under which tcsd runs.";
};
stateDir = mkOption {
default = "/var/lib/tpm";
type = types.path;
description = ''
The location of the system persistent storage file.
The system persistent storage file holds keys and data across
restarts of the TCSD and system reboots.
'';
};
firmwarePCRs = mkOption {
default = "0,1,2,3,4,5,6,7";
type = types.str;
description = "PCR indices used in the TPM for firmware measurements.";
};
kernelPCRs = mkOption {
default = "8,9,10,11,12";
type = types.str;
description = "PCR indices used in the TPM for kernel measurements.";
};
platformCred = mkOption {
default = "${cfg.stateDir}/platform.cert";
type = types.path;
description = ''
Path to the platform credential for your TPM. Your TPM
manufacturer may have provided you with a set of credentials
(certificates) that should be used when creating identities
using your TPM. When a user of your TPM makes an identity,
this credential will be encrypted as part of that process.
See the 1.1b TPM Main specification section 9.3 for information
on this process. '';
};
conformanceCred = mkOption {
default = "${cfg.stateDir}/conformance.cert";
type = types.path;
description = ''
Path to the conformance credential for your TPM.
See also the platformCred option'';
};
endorsementCred = mkOption {
default = "${cfg.stateDir}/endorsement.cert";
type = types.path;
description = ''
Path to the endorsement credential for your TPM.
See also the platformCred option'';
};
};
};
###### implementation
config = mkIf cfg.enable {
environment.systemPackages = [ pkgs.trousers ];
services.udev.extraRules = ''
# Give tcsd ownership of all TPM devices
KERNEL=="tpm[0-9]*", MODE="0660", OWNER="${cfg.user}", GROUP="${cfg.group}"
# Tag TPM devices to create a .device unit for tcsd to depend on
ACTION=="add", KERNEL=="tpm[0-9]*", TAG+="systemd"
'';
systemd.tmpfiles.rules = [
# Initialise the state directory
"d ${cfg.stateDir} 0770 ${cfg.user} ${cfg.group} - -"
];
systemd.services.tcsd = {
description = "Manager for Trusted Computing resources";
documentation = [ "man:tcsd(8)" ];
requires = [ "dev-tpm0.device" ];
after = [ "dev-tpm0.device" ];
wantedBy = [ "multi-user.target" ];
serviceConfig = {
User = cfg.user;
Group = cfg.group;
ExecStart = "${pkgs.trousers}/sbin/tcsd -f -c ${tcsdConf}";
};
};
users.users = optionalAttrs (cfg.user == "tss") {
tss = {
group = "tss";
uid = config.ids.uids.tss;
};
};
users.groups = optionalAttrs (cfg.group == "tss") {
tss.gid = config.ids.gids.tss;
};
};
}