idiosyn/nixos/module/kernel.nix

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{ self, ... }: { lib, pkgs, ... }: {
boot.consoleLogLevel = lib.mkDefault 3;
boot.initrd = {
checkJournalingFS = lib.mkDefault false;
includeDefaultModules = lib.mkDefault false;
luks.cryptoModules = lib.mkDefault [ ];
verbose = lib.mkDefault false;
};
boot.kernelPackages = lib.mkDefault
(pkgs.linuxPackagesFor self.packages.${pkgs.system}.linux-hardened);
boot.modprobeConfig.enable = lib.mkDefault false;
boot.kernelParams = [
# Disable kernel messages on the console
"quiet"
# Zerofill page and slab allocations on free
"init_on_free=1"
# Disable I/O delay
"io_delay=none"
# Enable page allocator free list randomisation
"page_alloc.shuffle=1"
# Disable slab merging
"slab_nomerge"
# Disable vsyscall mechanism
"vsyscall=none"
# Enable transparent hugepages
"transparent_hugepage=always"
# Suspend USB devices without delay
"usbcore.autosuspend=0"
];
boot.kernel.sysctl = {
# Mitigate some TOCTOU vulnerabilities
"fs.protected_fifos" = 2;
"fs.protected_hardlinks" = 1;
"fs.protected_regular" = 2;
"fs.protected_symlinks" = 1;
# Disable automatic loading of TTY line disciplines
"dev.tty.ldisc_autoload" = 0;
# Disable first 64KiB of virtual memory for allocation
"vm.mmap_min_addr" = 65536;
# Increase ASLR randomisation
"vm.mmap_rnd_bits" = 32;
"vm.mmap_rnd_compat_bits" = 16;
# Restrict ptrace()
"kernel.yama.ptrace_scope" = 1;
# Hide kernel memory addresses
"kernel.kptr_restrict" = 2;
# Restrict kernel log access
"kernel.dmesg_restrict" = 1;
# Enable hardened eBPF JIT
"kernel.unprivileged_bpf_disabled" = 1;
"net.core.bpf_jit_enable" = 1;
"net.core.bpf_jit_harden" = 2;
# Ignore ICMP redirects
"net.ipv4.conf.default.accept_redirects" = 0;
"net.ipv6.conf.default.accept_redirects" = 0;
"net.ipv4.conf.all.accept_redirects" = 0;
"net.ipv6.conf.all.accept_redirects" = 0;
# Set default Qdisc
"net.core.default_qdisc" = "fq";
# Increase minimum PMTU
"net.ipv4.route.min_pmtu" = 1280;
# Set default TCP congestion control algorithm
"net.ipv4.tcp_congestion_control" = "bbr";
# Enable ECN
"net.ipv4.tcp_ecn" = 1;
# Enable TCP fast open
"net.ipv4.tcp_fastopen" = 3;
# Disable TCP slow start after idling
"net.ipv4.tcp_slow_start_after_idle" = 0;
# Allow reuse of TCP ports during TIME-WAIT
"net.ipv4.tcp_tw_reuse" = 1;
# Enable TCP MTU probing
"net.ipv4.tcp_mtu_probing" = 1;
"net.ipv4.tcp_mtu_probe_floor" = 1220;
# Increase socket buffer space
# default of 16MiB should be sufficient to saturate 1GE
# maximum for 54MiB sufficient for 10GE
"net.core.rmem_default" = 16777216;
"net.core.rmem_max" = 56623104;
"net.core.wmem_default" = 16777216;
"net.core.wmem_max" = 56623104;
"net.core.optmem_max" = 65536;
"net.ipv4.tcp_rmem" = "4096 1048576 56623104";
"net.ipv4.tcp_wmem" = "4096 65536 56623104";
"net.ipv4.tcp_notsent_lowat" = 16384;
"net.ipv4.udp_rmem_min" = 9216;
"net.ipv4.udp_wmem_min" = 9216;
# Reduce TCP keepalive timeout to 2 minutes
"net.ipv4.tcp_keepalive_time" = 60;
"net.ipv4.tcp_keepalive_probes" = 6;
"net.ipv4.tcp_keepalive_intvl" = 10;
# Widen local port range
"net.ipv4.ip_local_port_range" = "16384 65535";
# Increase default MTU
"net.ipv6.conf.default.mtu" = 1452;
"net.ipv6.conf.all.mtu" = 1452;
# Set traffic class for NDP to CS6 (network control)
"net.ipv6.conf.default.ndisc_tclass" = 192;
"net.ipv6.conf.all.ndisc_tclass" = 192;
# Dirty page cache ratio
"vm.dirty_background_ratio" = 3;
"vm.dirty_ratio" = 6;
};
# Work around initrd generation bug
environment.etc."modprobe.d/nixos.conf".text = "";
systemd.tmpfiles.rules = [
"w- /sys/kernel/mm/transparent_hugepage/enabled - - - - always"
"w- /sys/kernel/mm/transparent_hugepage/defrag - - - - defer"
"w- /sys/kernel/mm/transparent_hugepage/shmem_enabled - - - - within_size"
];
}