85 lines
3 KiB
Nix
85 lines
3 KiB
Nix
# A profile with most (vanilla) hardening options enabled by default,
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# potentially at the cost of features and performance.
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{ config, lib, pkgs, ... }:
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with lib;
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{
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boot.kernelPackages = mkDefault pkgs.linuxPackages_hardened;
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security.hideProcessInformation = mkDefault true;
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security.lockKernelModules = mkDefault true;
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security.apparmor.enable = mkDefault true;
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boot.kernelParams = [
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# Overwrite free'd memory
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"page_poison=1"
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# Disable legacy virtual syscalls
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"vsyscall=none"
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# Disable hibernation (allows replacing the running kernel)
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"nohibernate"
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];
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boot.blacklistedKernelModules = [
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# Obscure network protocols
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"ax25"
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"netrom"
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"rose"
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];
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# Restrict ptrace() usage to processes with a pre-defined relationship
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# (e.g., parent/child)
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boot.kernel.sysctl."kernel.yama.ptrace_scope" = mkOverride 500 1;
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# Prevent replacing the running kernel image w/o reboot
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boot.kernel.sysctl."kernel.kexec_load_disabled" = mkDefault true;
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# Restrict access to kernel ring buffer (information leaks)
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boot.kernel.sysctl."kernel.dmesg_restrict" = mkDefault true;
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# Hide kptrs even for processes with CAP_SYSLOG
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boot.kernel.sysctl."kernel.kptr_restrict" = mkOverride 500 2;
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# Unprivileged access to bpf() has been used for privilege escalation in
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# the past
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boot.kernel.sysctl."kernel.unprivileged_bpf_disabled" = mkDefault true;
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# Disable bpf() JIT (to eliminate spray attacks)
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boot.kernel.sysctl."net.core.bpf_jit_enable" = mkDefault false;
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# ... or at least apply some hardening to it
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boot.kernel.sysctl."net.core.bpf_jit_harden" = mkDefault true;
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# A recurring problem with user namespaces is that there are
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# still code paths where the kernel's permission checking logic
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# fails to account for namespacing, instead permitting a
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# namespaced process to act outside the namespace with the
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# same privileges as it would have inside it. This is particularly
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# bad in the common case of running as root within the namespace.
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#
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# Setting the number of allowed user namespaces to 0 effectively disables
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# the feature at runtime. Attempting to create a user namespace
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# with unshare will then fail with "no space left on device".
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boot.kernel.sysctl."user.max_user_namespaces" = mkDefault 0;
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# Raise ASLR entropy for 64bit & 32bit, respectively.
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#
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# Note: mmap_rnd_compat_bits may not exist on 64bit.
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boot.kernel.sysctl."vm.mmap_rnd_bits" = mkDefault 32;
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boot.kernel.sysctl."vm.mmap_rnd_compat_bits" = mkDefault 16;
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# Allowing users to mmap() memory starting at virtual address 0 can turn a
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# NULL dereference bug in the kernel into code execution with elevated
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# privilege. Mitigate by enforcing a minimum base addr beyond the NULL memory
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# space. This breaks applications that require mapping the 0 page, such as
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# dosemu or running 16bit applications under wine. It also breaks older
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# versions of qemu.
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#
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# The value is taken from the KSPP recommendations (Debian uses 4096).
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boot.kernel.sysctl."vm.mmap_min_addr" = mkDefault 65536;
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}
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