122 lines
4 KiB
Nix
122 lines
4 KiB
Nix
{ config, pkgs, lib, ... }:
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with lib;
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let
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cfg = config.security.grsecurity;
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grsecLockPath = "/proc/sys/kernel/grsecurity/grsec_lock";
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# Ascertain whether ZFS is required for booting the system; grsecurity is
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# currently incompatible with ZFS, rendering the system unbootable.
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zfsNeededForBoot = filter
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(fs: (fs.neededForBoot
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|| elem fs.mountPoint [ "/" "/nix" "/nix/store" "/var" "/var/log" "/var/lib" "/etc" ])
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&& fs.fsType == "zfs")
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(attrValues config.fileSystems) != [];
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# Ascertain whether NixOS container support is required
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containerSupportRequired =
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config.boot.enableContainers && config.containers != {};
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in
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{
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options.security.grsecurity = {
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enable = mkEnableOption "Grsecurity/PaX";
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lockTunables = mkOption {
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type = types.bool;
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example = false;
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default = true;
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description = ''
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Whether to automatically lock grsecurity tunables
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(<option>boot.kernel.sysctl."kernel.grsecurity.*"</option>). Disable
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this to allow configuration of grsecurity features while the system is
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running. The lock can be manually engaged by activating the
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<literal>grsec-lock</literal> service unit.
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'';
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};
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};
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config = mkIf cfg.enable {
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# Allow the user to select a different package set, subject to the stated
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# required kernel config
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boot.kernelPackages = mkDefault pkgs.linuxPackages_grsec_nixos;
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system.requiredKernelConfig = with config.lib.kernelConfig;
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[ (isEnabled "GRKERNSEC")
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(isEnabled "PAX")
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(isYES "GRKERNSEC_SYSCTL")
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(isYES "GRKERNSEC_SYSCTL_DISTRO")
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];
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# Install PaX related utillities into the system profile. Eventually, we
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# also want to include gradm here.
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environment.systemPackages = with pkgs; [ paxctl pax-utils ];
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# Install rules for the grsec device node
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services.udev.packages = [ pkgs.gradm ];
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# This service unit is responsible for locking the Grsecurity tunables. The
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# unit is always defined, but only activated on bootup if lockTunables is
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# toggled. When lockTunables is toggled, failure to activate the unit will
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# enter emergency mode. The intent is to make it difficult to silently
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# enter multi-user mode without having locked the tunables. Some effort is
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# made to ensure that starting the unit is an idempotent operation.
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systemd.services.grsec-lock = {
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description = "Lock grsecurity tunables";
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wantedBy = optional cfg.lockTunables "multi-user.target";
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wants = [ "local-fs.target" "systemd-sysctl.service" ];
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after = [ "local-fs.target" "systemd-sysctl.service" ];
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conflicts = [ "shutdown.target" ];
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restartIfChanged = false;
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script = ''
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if ${pkgs.gnugrep}/bin/grep -Fq 0 ${grsecLockPath} ; then
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echo -n 1 > ${grsecLockPath}
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fi
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'';
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unitConfig = {
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ConditionPathIsReadWrite = grsecLockPath;
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DefaultDependencies = false;
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} // optionalAttrs cfg.lockTunables {
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OnFailure = "emergency.target";
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};
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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};
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};
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# Configure system tunables
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boot.kernel.sysctl = {
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# Removed under grsecurity
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"kernel.kptr_restrict" = mkForce null;
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} // optionalAttrs config.nix.useSandbox {
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# chroot(2) restrictions that conflict with sandboxed Nix builds
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"kernel.grsecurity.chroot_caps" = mkForce 0;
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"kernel.grsecurity.chroot_deny_chroot" = mkForce 0;
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"kernel.grsecurity.chroot_deny_mount" = mkForce 0;
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"kernel.grsecurity.chroot_deny_pivot" = mkForce 0;
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} // optionalAttrs containerSupportRequired {
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# chroot(2) restrictions that conflict with NixOS lightweight containers
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"kernel.grsecurity.chroot_deny_chmod" = mkForce 0;
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"kernel.grsecurity.chroot_deny_mount" = mkForce 0;
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"kernel.grsecurity.chroot_restrict_nice" = mkForce 0;
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};
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assertions = [
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{ assertion = !zfsNeededForBoot;
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message = "grsecurity is currently incompatible with ZFS";
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}
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];
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};
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}
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