e9761fa327
For the hardened profile enable flushing whenever the hypervisor enters the guest, but otherwise leave at kernel default (conditional flushing as of writing).
96 lines
3.4 KiB
Nix
96 lines
3.4 KiB
Nix
{ config, lib, ... }:
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with lib;
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{
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meta = {
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maintainers = [ maintainers.joachifm ];
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};
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options = {
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security.allowUserNamespaces = mkOption {
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type = types.bool;
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default = true;
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description = ''
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Whether to allow creation of user namespaces. A recurring problem
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with user namespaces is the presence of code paths where the kernel's
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permission checking logic fails to account for namespacing, instead
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permitting a 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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damaging in the common case of running as root within the namespace.
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When user namespace creation is disallowed, attempting to create
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a user namespace fails with "no space left on device" (ENOSPC).
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'';
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};
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security.protectKernelImage = mkOption {
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type = types.bool;
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default = false;
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description = ''
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Whether to prevent replacing the running kernel image.
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'';
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};
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security.virtualization.flushL1DataCache = mkOption {
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type = types.nullOr (types.enum [ "never" "cond" "always" ]);
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default = null;
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description = ''
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Whether the hypervisor should flush the L1 data cache before
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entering guests.
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</para>
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<para>
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<variablelist>
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<varlistentry>
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<term><literal>null</literal></term>
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<listitem><para>uses the kernel default</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>"never"</literal></term>
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<listitem><para>disables L1 data cache flushing entirely.
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May be appropriate if all guests are trusted.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>"cond"</literal></term>
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<listitem><para>flushes L1 data cache only for pre-determined
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code paths. May leak information about the host address space
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layout.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>"always"</literal></term>
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<listitem><para>flushes L1 data cache every time the hypervisor
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enters the guest. May incur significant performance cost.
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</para></listitem>
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</varlistentry>
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</variablelist>
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'';
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};
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};
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config = mkMerge [
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(mkIf (!config.security.allowUserNamespaces) {
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# Setting the number of allowed user namespaces to 0 effectively disables
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# the feature at runtime. Note that root may raise the limit again
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# at any time.
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boot.kernel.sysctl."user.max_user_namespaces" = 0;
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assertions = [
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{ assertion = config.nix.useSandbox -> config.security.allowUserNamespaces;
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message = "`nix.useSandbox = true` conflicts with `!security.allowUserNamespaces`.";
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}
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];
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})
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(mkIf config.security.protectKernelImage {
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# Disable hibernation (allows replacing the running kernel)
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boot.kernelParams = [ "nohibernate" ];
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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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})
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(mkIf (config.security.virtualization.flushL1DataCache != null) {
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boot.kernelParams = [ "kvm-intel.vmentry_l1d_flush=${config.security.virtualization.flushL1DataCache}" ];
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})
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];
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}
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