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

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

## 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), redzoning (Z) and poisoning (P).
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX slub_debug=FZP"

if command -v "qubesdb-read" >/dev/null 2>&1 ; then
   ## https://github.com/QubesOS/qubes-issues/issues/5212#issuecomment-533873012
   true "skip adding page_poison=1 in Qubes"
else
   ## Wipes free memory so it can't leak in various ways and prevents some use-after-free vulnerabilites.
   GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX page_poison=1"
fi

## Makes the kernel panic on uncorrectable errors in ECC memory that an attacker could exploit.
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"

## Enables all mitigations for the MDS vulnerability.
## Disables smt which can be used to exploit the MDS vulnerability.
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX mds=full,nosmt"