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nixos/hardened: make pti=on overridable

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Introduces a new security.forcePageTableIsolation option (default false
on !hardened, true on hardened) that forces pti=on.
This commit is contained in:
Pierre Bourdon 2019-07-30 02:24:56 +02:00
parent fd2b2b5cd5
commit 67b7e70865
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GPG key ID: 6FB80DCD84DA0F1C
2 changed files with 18 additions and 3 deletions
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5
nixos/modules/profiles/hardened.nix
View file

@ -26,6 +26,8 @@ with lib;
security.allowSimultaneousMultithreading = mkDefault false;
security.forcePageTableIsolation = mkDefault true;
security.virtualisation.flushL1DataCache = mkDefault "always";
security.apparmor.enable = mkDefault true;
@ -42,9 +44,6 @@ with lib;
# Disable legacy virtual syscalls
"vsyscall=none"
# Enable PTI even if CPU claims to be safe from meltdown
"pti=on"
];
boot.blacklistedKernelModules = [

16
nixos/modules/security/misc.nix
View file

@ -54,6 +54,18 @@ with lib;
'';
};
security.forcePageTableIsolation = mkOption {
type = types.bool;
default = false;
description = ''
Whether to force-enable the Page Table Isolation (PTI) Linux kernel
feature even on CPU models that claim to be safe from Meltdown.
This hardening feature is most beneficial to systems that run untrusted
workloads that rely on address space isolation for security.
'';
};
security.virtualisation.flushL1DataCache = mkOption {
type = types.nullOr (types.enum [ "never" "cond" "always" ]);
default = null;
@ -114,6 +126,10 @@ with lib;
boot.kernelParams = [ "nosmt" ];
})
(mkIf config.security.forcePageTableIsolation {
boot.kernelParams = [ "pti=on" ];
})
(mkIf (config.security.virtualisation.flushL1DataCache != null) {
boot.kernelParams = [ "kvm-intel.vmentry_l1d_flush=${config.security.virtualisation.flushL1DataCache}" ];
})