dotfiles/nixos/security.nix

{
  config,
  pkgs,
  lib,
  ...
}: {
  networking.firewall.checkReversePath = "loose";
  networking.firewall.enable = true;

  nix.settings.allowed-users = ["@users"];

  security = {
    apparmor.enable = true;
    apparmor.killUnconfinedConfinables = true;
    forcePageTableIsolation = true;
    lockKernelModules = false;
    protectKernelImage = true;
    virtualisation.flushL1DataCache = "always";
  };

  sops.age = {
    keyFile = "/var/lib/sops-nix/key.txt";
    generateKey = true;
  };

  boot = {
    kernelParams = ["slub_debug=FZP" "page_poison=1" "page_alloc.shuffle=1"];

    blacklistedKernelModules = [
      # Obscure network protocols
      "ax25"
      "netrom"
      "rose"

      # Old or rare or insufficiently audited filesystems
      "adfs"
      "affs"
      "bfs"
      "befs"
      "cramfs"
      "efs"
      "erofs"
      "exofs"
      "freevxfs"
      "f2fs"
      "hfs"
      "hpfs"
      "jfs"
      "minix"
      "nilfs2"
      "omfs"
      "qnx4"
      "qnx6"
      "sysv"
      "ufs"
    ];

    kernel.sysctl = {
      # Restrict ptrace() usage to processes with a pre-defined relationship
      # (e.g., parent/child)
      "kernel.yama.ptrace_scope" = lib.mkOverride 500 1;

      # Hide kptrs even for processes with CAP_SYSLOG
      "kernel.kptr_restrict" = lib.mkOverride 500 2;

      # Disable bpf() JIT (to eliminate spray attacks)
      "net.core.bpf_jit_enable" = false;

      # Disable ftrace debugging
      "kernel.ftrace_enabled" = false;

      # Enable strict reverse path filtering (that is, do not attempt to route
      # packets that "obviously" do not belong to the iface's network; dropped
      # packets are logged as martians).
      "net.ipv4.conf.all.log_martians" = true;
      "net.ipv4.conf.all.rp_filter" = "1";
      "net.ipv4.conf.default.log_martians" = true;
      "net.ipv4.conf.default.rp_filter" = "1";

      # Ignore broadcast ICMP (mitigate SMURF)
      "net.ipv4.icmp_echo_ignore_broadcasts" = true;

      # Ignore incoming ICMP redirects (note: default is needed to ensure that the
      # setting is applied to interfaces added after the sysctls are set)
      "net.ipv4.conf.all.accept_redirects" = false;
      "net.ipv4.conf.all.secure_redirects" = false;
      "net.ipv4.conf.default.accept_redirects" = false;
      "net.ipv4.conf.default.secure_redirects" = false;
      "net.ipv6.conf.all.accept_redirects" = false;
      "net.ipv6.conf.default.accept_redirects" = false;

      # Ignore outgoing ICMP redirects (this is ipv4 only)
      "net.ipv4.conf.all.send_redirects" = false;
      "net.ipv4.conf.default.send_redirects" = false;
    };
  };
}