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nixos/security/misc: factor out protectKernelImage

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Introduces the option security.protectKernelImage that is intended to control
various mitigations to protect the integrity of the running kernel
image (i.e., prevent replacing it without rebooting).

This makes sense as a dedicated module as it is otherwise somewhat difficult
to override for hardened profile users who want e.g., hibernation to work.
This commit is contained in:
Joachim Fasting 2018-12-16 10:37:36 +01:00
parent 9db84f6fcd
commit 84fb8820db
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GPG Key ID: 5C204DF675C90294
3 changed files with 23 additions and 6 deletions
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8
nixos/modules/profiles/hardened.nix
View File

@ -20,6 +20,8 @@ with lib;
security.allowUserNamespaces = mkDefault false;
security.protectKernelImage = mkDefault true;
security.apparmor.enable = mkDefault true;
boot.kernelParams = [
@ -28,9 +30,6 @@ with lib;
# Disable legacy virtual syscalls
"vsyscall=none"
# Disable hibernation (allows replacing the running kernel)
"nohibernate"
];
boot.blacklistedKernelModules = [
@ -44,9 +43,6 @@ with lib;
# (e.g., parent/child)
boot.kernel.sysctl."kernel.yama.ptrace_scope" = mkOverride 500 1;
# Prevent replacing the running kernel image w/o reboot
boot.kernel.sysctl."kernel.kexec_load_disabled" = mkDefault true;
# Restrict access to kernel ring buffer (information leaks)
boot.kernel.sysctl."kernel.dmesg_restrict" = mkDefault true;

15
nixos/modules/security/misc.nix
View File

@ -22,6 +22,14 @@ with lib;
a user namespace fails with "no space left on device" (ENOSPC).
'';
};
security.protectKernelImage = mkOption {
type = types.bool;
default = false;
description = ''
Whether to prevent replacing the running kernel image.
'';
};
};
config = mkMerge [
@ -37,5 +45,12 @@ with lib;
}
];
})
(mkIf config.security.protectKernelImage {
# Disable hibernation (allows replacing the running kernel)
boot.kernelParams = [ "nohibernate" ];
# Prevent replacing the running kernel image w/o reboot
boot.kernel.sysctl."kernel.kexec_load_disabled" = mkDefault true;
})
];
}

6
nixos/tests/hardened.nix
View File

@ -70,5 +70,11 @@ import ./make-test.nix ({ pkgs, ...} : {
$machine->fail("su -l nobody -s /bin/sh -c 'nix ping-store'");
$machine->succeed("su -l alice -c 'nix ping-store'") =~ "OK";
};
# Test kernel image protection
subtest "kernelimage", sub {
$machine->fail("systemctl hibernate");
$machine->fail("systemctl kexec");
};
'';
})