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# A profile with most (vanilla) hardening options enabled by default,
# potentially at the cost of features and performance.
{ lib, pkgs, ... }:
with lib;
{
meta = {
maintainers = [ maintainers.joachifm ];
};
boot.kernelPackages = mkDefault pkgs.linuxPackages_hardened;
nix.allowedUsers = mkDefault [ "@users" ];
security.hideProcessInformation = mkDefault true;
security.lockKernelModules = mkDefault true;
security.allowUserNamespaces = mkDefault false;
security.protectKernelImage = mkDefault true;
security.allowSimultaneousMultithreading = mkDefault false;
security.forcePageTableIsolation = mkDefault true;
security.virtualisation.flushL1DataCache = mkDefault "always";
security.apparmor.enable = mkDefault true;
boot.kernelParams = [
# Slab/slub sanity checks, redzoning, and poisoning
"slub_debug=FZP"
# Disable slab merging to make certain heap overflow attacks harder
"slab_nomerge"
# Overwrite free'd memory
"page_poison=1"
# Disable legacy virtual syscalls
"vsyscall=none"
# Enable page allocator randomization
"page_alloc.shuffle=1"
];
boot.blacklistedKernelModules = [
# Obscure network protocols
"ax25"
"netrom"
"rose"
];
# Restrict ptrace() usage to processes with a pre-defined relationship
# (e.g., parent/child)
boot.kernel.sysctl."kernel.yama.ptrace_scope" = mkOverride 500 1;
# 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;
# Raise ASLR entropy for 64bit & 32bit, respectively.
#
# Note: mmap_rnd_compat_bits may not exist on 64bit.
boot.kernel.sysctl."vm.mmap_rnd_bits" = mkDefault 32;
boot.kernel.sysctl."vm.mmap_rnd_compat_bits" = mkDefault 16;
# Allowing users to mmap() memory starting at virtual address 0 can turn a
# NULL dereference bug in the kernel into code execution with elevated
# privilege. Mitigate by enforcing a minimum base addr beyond the NULL memory
# space. This breaks applications that require mapping the 0 page, such as
# dosemu or running 16bit applications under wine. It also breaks older
# versions of qemu.
#
# The value is taken from the KSPP recommendations (Debian uses 4096).
boot.kernel.sysctl."vm.mmap_min_addr" = mkDefault 65536;
# Disable ftrace debugging
boot.kernel.sysctl."kernel.ftrace_enabled" = mkDefault 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).
boot.kernel.sysctl."net.ipv4.conf.all.log_martians" = mkDefault true;
boot.kernel.sysctl."net.ipv4.conf.all.rp_filter" = mkDefault "1";
boot.kernel.sysctl."net.ipv4.conf.default.log_martians" = mkDefault true;
boot.kernel.sysctl."net.ipv4.conf.default.rp_filter" = mkDefault "1";
# Ignore broadcast ICMP (mitigate SMURF)
boot.kernel.sysctl."net.ipv4.icmp_echo_ignore_broadcasts" = mkDefault true;
# Ignore incoming ICMP redirects (note: default is needed to ensure that the
# setting is applied to interfaces added after the sysctls are set)
boot.kernel.sysctl."net.ipv4.conf.all.accept_redirects" = mkDefault false;
boot.kernel.sysctl."net.ipv4.conf.all.secure_redirects" = mkDefault false;
boot.kernel.sysctl."net.ipv4.conf.default.accept_redirects" = mkDefault false;
boot.kernel.sysctl."net.ipv4.conf.default.secure_redirects" = mkDefault false;
boot.kernel.sysctl."net.ipv6.conf.all.accept_redirects" = mkDefault false;
boot.kernel.sysctl."net.ipv6.conf.default.accept_redirects" = mkDefault false;
# Ignore outgoing ICMP redirects (this is ipv4 only)
boot.kernel.sysctl."net.ipv4.conf.all.send_redirects" = mkDefault false;
boot.kernel.sysctl."net.ipv4.conf.default.send_redirects" = mkDefault false;
# Restrict userfaultfd syscalls to processes with the SYS_PTRACE capability
boot.kernel.sysctl."vm.unprivileged_userfaultfd" = mkDefault false;
}
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