security-misc/etc/default/grub.d/40_kernel_hardening.cfg

## Copyright (C) 2019 - 2023 ENCRYPTED SUPPORT LP <adrelanos@whonix.org>
## See the file COPYING for copying conditions.

kpkg="linux-image-$(dpkg --print-architecture)" || true
kver="$(dpkg-query --show --showformat='${Version}' "$kpkg")" 2>/dev/null || true
#echo "## kver: $kver"

## Disables the merging of slabs of similar sizes.
## Sometimes a slab can be used in a vulnerable way which an attacker can exploit.
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX slab_nomerge"

## Enables sanity checks (F) and redzoning (Z).
## Disabled due to kernel deciding to implicitly disable kernel pointer hashing
## https://github.com/torvalds/linux/commit/792702911f581f7793962fbeb99d5c3a1b28f4c3
#GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX slub_debug=FZ"

## Zero memory at allocation and free time.
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX init_on_alloc=1 init_on_free=1"

## Machine check exception handler decides whether the system should panic or not based on the exception that happened.
## https://forums.whonix.org/t/kernel-hardening/7296/494
#GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX mce=0"

## Enables Kernel Page Table Isolation which mitigates Meltdown and improves KASLR.
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX pti=on"

## Vsyscalls are obsolete, are at fixed addresses and are a target for ROP.
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX vsyscall=none"

## Enables page allocator freelist randomization.
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX page_alloc.shuffle=1"

## Enables randomisation of the kernel stack offset on syscall entries (introduced in kernel 5.13).
## https://lkml.org/lkml/2019/3/18/246
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX randomize_kstack_offset=on"

## Enables kernel lockdown.
##
## Disabled for now as it enforces module signature verification which breaks
## too many things.
## https://forums.whonix.org/t/enforce-kernel-module-software-signature-verification-module-signing-disallow-kernel-module-loading-by-default/7880
##
#if dpkg --compare-versions "${kver}" ge "5.4"; then
#  GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX lockdown=confidentiality"
#fi

## Gather more entropy during boot.
##
## Requires linux-hardened kernel patch.
## https://github.com/anthraxx/linux-hardened
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX extra_latent_entropy"

## Restrict access to debugfs since it can contain a lot of sensitive information.
## https://lkml.org/lkml/2020/7/16/122
## https://github.com/torvalds/linux/blob/fb1201aececc59990b75ef59fca93ae4aa1e1444/Documentation/admin-guide/kernel-parameters.txt#L835-L848
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX debugfs=off"

## Force the kernel to panic on "oopses" (which may be due to false positives)
## https://forums.whonix.org/t/set-oops-panic-kernel-parameter-or-kernel-panic-on-oops-1-sysctl-for-better-security/7713
## Implemented differently:
## /usr/libexec/security-misc/panic-on-oops
#GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX oops=panic"