nixpkgs/nixos/modules/profiles/hardened.nix

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# A profile with most (vanilla) hardening options enabled by default,
# potentially at the cost of features and performance.
{ config, lib, pkgs, ... }:
with lib;
{
boot.kernelPackages = mkDefault pkgs.linuxPackages_hardened;
security.hideProcessInformation = mkDefault true;
security.lockKernelModules = mkDefault true;
security.apparmor.enable = mkDefault true;
boot.kernelParams = [
# Overwrite free'd memory
"page_poison=1"
# Disable legacy virtual syscalls
"vsyscall=none"
# Disable hibernation (allows replacing the running kernel)
"nohibernate"
];
# Restrict ptrace() usage to processes with a pre-defined relationship
# (e.g., parent/child)
boot.kernel.sysctl."kernel.yama.ptrace_scope" = mkOverride 500 1;
# Prevent replacing the running kernel image w/o reboot
boot.kernel.sysctl."kernel.kexec_load_disabled" = mkDefault true;
# Restrict access to kernel ring buffer (information leaks)
boot.kernel.sysctl."kernel.dmesg_restrict" = mkDefault true;
# Hide kptrs even for processes with CAP_SYSLOG
boot.kernel.sysctl."kernel.kptr_restrict" = mkOverride 500 2;
# Unprivileged access to bpf() has been used for privilege escalation in
# the past
boot.kernel.sysctl."kernel.unprivileged_bpf_disabled" = mkDefault true;
# Disable bpf() JIT (to eliminate spray attacks)
boot.kernel.sysctl."net.core.bpf_jit_enable" = mkDefault false;
# ... or at least apply some hardening to it
boot.kernel.sysctl."net.core.bpf_jit_harden" = mkDefault true;
# A recurring problem with user namespaces is that there are
# still code paths where the kernel's permission checking logic
# fails to account for namespacing, instead permitting a
# namespaced process to act outside the namespace with the
# same privileges as it would have inside it. This is particularly
# bad in the common case of running as root within the namespace.
#
# Setting the number of allowed userns to 0 effectively disables
# the feature at runtime. Attempting to create a user namespace
# with unshare will then fail with "no space left on device".
boot.kernel.sysctl."user.max_user_namespaces" = mkDefault 0;
}