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# Based on recommendations from:
# http://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project#Recommended_settings
# https://wiki.gentoo.org/wiki/Hardened/Hardened_Kernel_Project
#
# Dangerous features that can be permanently (for the boot session) disabled at
# boot via sysctl or kernel cmdline are left enabled here, for improved
# flexibility.
#
# See also <nixos/modules/profiles/hardened.nix>
{ lib, version }:
with lib;
with lib.kernel;
with (lib.kernel.whenHelpers version);
assert (versionAtLeast version "4.9");
{
# Report BUG() conditions and kill the offending process.
BUG = yes;
# Safer page access permissions (wrt. code injection). Default on >=4.11.
DEBUG_RODATA = whenOlder "4.11" yes;
DEBUG_SET_MODULE_RONX = whenOlder "4.11" yes;
# Mark LSM hooks read-only after init. SECURITY_WRITABLE_HOOKS n
# conflicts with SECURITY_SELINUX_DISABLE y; disabling the latter
# implicitly marks LSM hooks read-only after init.
#
# SELinux can only be disabled at boot via selinux=0
#
# We set SECURITY_WRITABLE_HOOKS n primarily for documentation purposes; the
# config builder fails to detect that it has indeed been unset.
SECURITY_SELINUX_DISABLE = whenAtLeast "4.12" no;
SECURITY_WRITABLE_HOOKS = whenAtLeast "4.12" (option no);
STRICT_KERNEL_RWX = whenAtLeast "4.11" yes;
# Perform additional validation of commonly targeted structures.
DEBUG_CREDENTIALS = yes;
DEBUG_NOTIFIERS = yes;
DEBUG_PI_LIST = whenOlder "5.2" yes; # doesn't BUG()
DEBUG_PLIST = whenAtLeast "5.2" yes;
DEBUG_SG = yes;
SCHED_STACK_END_CHECK = yes;
REFCOUNT_FULL = whenBetween "4.13" "5.5" yes;
# Randomize page allocator when page_alloc.shuffle=1
SHUFFLE_PAGE_ALLOCATOR = whenAtLeast "5.2" yes;
# Allow enabling slub/slab free poisoning with slub_debug=P
SLUB_DEBUG = yes;
# Wipe higher-level memory allocations on free() with page_poison=1
PAGE_POISONING = yes;
PAGE_POISONING_NO_SANITY = whenOlder "5.11" yes;
PAGE_POISONING_ZERO = whenOlder "5.11" yes;
# Enable the SafeSetId LSM
SECURITY_SAFESETID = whenAtLeast "5.1" yes;
# Reboot devices immediately if kernel experiences an Oops.
PANIC_TIMEOUT = freeform "-1";
GCC_PLUGINS = yes; # Enable gcc plugin options
# Gather additional entropy at boot time for systems that may not have appropriate entropy sources.
GCC_PLUGIN_LATENT_ENTROPY = yes;
GCC_PLUGIN_STRUCTLEAK = whenAtLeast "4.11" yes; # A port of the PaX structleak plugin
GCC_PLUGIN_STRUCTLEAK_BYREF_ALL = whenAtLeast "4.14" yes; # Also cover structs passed by address
GCC_PLUGIN_STACKLEAK = whenAtLeast "4.20" yes; # A port of the PaX stackleak plugin
GCC_PLUGIN_RANDSTRUCT = whenAtLeast "4.13" yes; # A port of the PaX randstruct plugin
GCC_PLUGIN_RANDSTRUCT_PERFORMANCE = whenAtLeast "4.13" yes;
# Disable various dangerous settings
ACPI_CUSTOM_METHOD = no; # Allows writing directly to physical memory
PROC_KCORE = no; # Exposes kernel text image layout
INET_DIAG = no; # Has been used for heap based attacks in the past
# INET_DIAG=n causes the following options to not exist anymore, but since they are defined in common-config.nix,
# make them optional
INET_DIAG_DESTROY = option no;
INET_RAW_DIAG = option no;
INET_TCP_DIAG = option no;
INET_UDP_DIAG = option no;
INET_MPTCP_DIAG = option no;
# Use -fstack-protector-strong (gcc 4.9+) for best stack canary coverage.
CC_STACKPROTECTOR_REGULAR = whenOlder "4.18" no;
CC_STACKPROTECTOR_STRONG = whenOlder "4.18" yes;
# Detect out-of-bound reads/writes and use-after-free
KFENCE = whenAtLeast "5.12" yes;
}
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