nixos/defaults/security.nix

   1 { inputs, pkgs, lib, config, ... }:
   2 {
   3 boot.kernelPackages = pkgs.linuxPackages_hardened;
   4 #environment.memoryAllocator.provider = "libc";
   5 nix.allowedUsers = [ "@users" ];
   6 networking.firewall.pingLimit = "--limit 60/minute --limit-burst 5";
   7 security.allowSimultaneousMultithreading = false;
   8 security.apparmor.enable = true;
   9 security.forcePageTableIsolation = true;
  10 security.lockKernelModules = lib.mkDefault true;
  11 security.protectKernelImage = true;
  12 security.virtualisation.flushL1DataCache = "always";
  13 boot.blacklistedKernelModules = [
  14   # Obscure network protocols
  15   "ax25"
  16   "netrom"
  17   "rose"
  18
  19   # Old or rare or insufficiently audited filesystems
  20   "adfs"
  21   "affs"
  22   "bfs"
  23   "befs"
  24   "cramfs"
  25   "efs"
  26   "erofs"
  27   "exofs"
  28   "freevxfs"
  29   "f2fs"
  30   "hfs"
  31   "hpfs"
  32   "jfs"
  33   "minix"
  34   "nilfs2"
  35   "ntfs"
  36   "omfs"
  37   "qnx4"
  38   "qnx6"
  39   "sysv"
  40   "ufs"
  41 ];
  42 boot.kernel.sysctl = {
  43   # Mitigate kernel pointer leaks
  44   "kernel.kptr_restrict" = 2;
  45   # Restricts the kernel log to the CAP_SYSLOG capability
  46   "kernel.dmesg_restrict" = 1;
  47   # Prevent information leaks
  48   #kernel.printk = "3 3 3 3";
  49   # Restrict eBPF to the CAP_BPF capability
  50   # and enable JIT hardening techniques
  51   # such as constant blinding.
  52   "kernel.unprivileged_bpf_disabled" = 1;
  53   "net.core.bpf_jit_harden" = 2;
  54   # Restricts loading TTY line disciplines
  55   # to the CAP_SYS_MODULE capability to prevent
  56   # unprivileged attackers from loading vulnerable
  57   # line disciplines with the TIOCSETD ioctl
  58   "dev.tty.ldisc_autoload" = 0;
  59   # The userfaultfd() syscall is often abused to exploit
  60   # use-after-free flaws.
  61   # Due to this, this sysctl is used to restrict
  62   # this syscall to the CAP_SYS_PTRACE capability.
  63   "vm.unprivileged_userfaultfd" = 0;
  64   # kexec is a system call that is used
  65   # to boot another kernel during runtime.
  66   "kernel.kexec_load_disabled" = 1;
  67   # User namespaces are a feature in the kernel which aim to
  68   # improve sandboxing and make it easily accessible for
  69   # unprivileged users however, this feature exposes
  70   # significant kernel attack surface for privilege
  71   # escalation so this sysctl restricts the usage of user
  72   # namespaces to the CAP_SYS_ADMIN capability.
  73   "kernel.unprivileged_userns_clone" = 0;
  74   # Restricts all usage of performance events to the
  75   # CAP_PERFMON capability
  76   "kernel.perf_event_paranoid" = 3;
  77   # Helps protect against SYN flood attacks
  78   "net.ipv4.tcp_syncookies" = 1;
  79   # Protects against time-wait assassination
  80   # by dropping RST packets for sockets
  81   # in the time-wait state.
  82   "net.ipv4.tcp_rfc1337" = 1;
  83   # Disable ICMP redirect acceptance and sending to prevent
  84   # man-in-the-middle attacks and minimize information disclosure.
  85   "net.ipv4.conf.all.accept_redirects" = 0;
  86   "net.ipv4.conf.default.accept_redirects" = 0;
  87   "net.ipv4.conf.all.secure_redirects" = 0;
  88   "net.ipv4.conf.default.secure_redirects" = 0;
  89   "net.ipv6.conf.all.accept_redirects" = 0;
  90   "net.ipv6.conf.default.accept_redirects" = 0;
  91   "net.ipv4.conf.all.send_redirects" = 0;
  92   "net.ipv4.conf.default.send_redirects" = 0;
  93   # Disable source routing, a mechanism
  94   # that allows users to redirect network traffic.
  95   "net.ipv4.conf.all.accept_source_route" = 0;
  96   "net.ipv4.conf.default.accept_source_route" = 0;
  97   "net.ipv6.conf.all.accept_source_route" = 0;
  98   "net.ipv6.conf.default.accept_source_route" = 0;
  99   /*
 100   # Disable TCP SACK, which is commonly exploited
 101   # and unnecessary for many circumstances.
 102   # https://serverfault.com/questions/10955/when-to-turn-tcp-sack-off
 103   "net.ipv4.tcp_sack" = 0;
 104   "net.ipv4.tcp_dsack" = 0;
 105   "net.ipv4.tcp_fack" = 0;
 106   */
 107   # Generate a random IPv6 address
 108   "net.ipv6.conf.all.use_tempaddr" = 2;
 109   "net.ipv6.conf.default.use_tempaddr" = 2;
 110   # Restricts usage of ptrace to only processes
 111   # with the CAP_SYS_PTRACE capability
 112   "kernel.yama.ptrace_scope" = 2;
 113   # Do source validation by confirming reverse path
 114   "net.ipv4.conf.all.rp_filter" = 1;
 115   "net.ipv4.conf.default.rp_filter" = 1;
 116 };
 117 boot.kernelParams = [
 118   "slab_nomerge"
 119   "slub_debug=FZ"
 120   #"init_on_alloc=1"
 121   #"init_on_free=1"
 122   "page_alloc.shuffle=1"
 123   "pti=on"
 124   "vsyscall=none"
 125   "debugfs=off"
 126   "oops=panic"
 127   # Disabled because zfs and wireguard modules are not signed
 128   "module.sig_enforce=0"
 129   "lockdown=confidentiality"
 130   "mce=0"
 131   #"quiet"
 132   #"loglevel=0"
 133 ];
 134 }