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

## Copyright (C) 2019 - 2024 ENCRYPTED SUPPORT LP <adrelanos@whonix.org>
## See the file COPYING for copying conditions.

## Enable known mitigations for CPU vulnerabilities.
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/index.html
## https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html
## https://forums.whonix.org/t/should-all-kernel-patches-for-cpu-bugs-be-unconditionally-enabled-vs-performance-vs-applicability/7647

## Check for potential updates directly from AMD and Intel.
## https://www.amd.com/en/resources/product-security.html
## https://www.intel.com/content/www/us/en/developer/topic-technology/software-security-guidance/advisory-guidance.html
## https://www.intel.com/content/www/us/en/developer/topic-technology/software-security-guidance/disclosure-documentation.html

## Enable a subset of known mitigations for CPU vulnerabilities and disable SMT.
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX mitigations=auto,nosmt"

## Disable SMT as it has been the cause of and amplified numerous CPU exploits.
## The only full mitigation of cross-HT attacks is to disable SMT.
## Disabling will significantly decrease system performance on multi-threaded tasks.
## To enable SMT, remove this line and all other occurrences of "nosmt" in this file.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/core-scheduling.html
## https://forums.whonix.org/t/should-all-kernel-patches-for-cpu-bugs-be-unconditionally-enabled-vs-performance-vs-applicability/7647/17
## https://github.com/anthraxx/linux-hardened/issues/37#issuecomment-619597365
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX nosmt=force"

## Enable mitigations for both Spectre Variant 2 (indirect branch speculation)
## and Intel branch history injection (BHI) vulnerabilities.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/spectre.html
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX spectre_v2=on"
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX spectre_bhi=on"

## Disable Speculative Store Bypass (Spectre Variant 4).
##
## https://www.suse.com/support/kb/doc/?id=000019189
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX spec_store_bypass_disable=on"

## Enable mitigations for the L1TF vulnerability through disabling SMT
## and L1D flush runtime control.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX l1tf=full,force"

## Enable mitigations for the MDS vulnerability through clearing buffer cache
## and disabling SMT.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX mds=full,nosmt"

## Patches the TAA vulnerability by disabling TSX and enables mitigations using
## TSX Async Abort along with disabling SMT.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX tsx=off"
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX tsx_async_abort=full,nosmt"

## Mark all huge pages in the EPT as non-executable to mitigate iTLB multihit.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/multihit.html
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX kvm.nx_huge_pages=force"

## Mitigations for SRBDS to prevent MDS attacks on RDRAND and RDSEED instructions
## are only possible through microcode updates from Intel.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/special-register-buffer-data-sampling.html
## https://access.redhat.com/solutions/5142691

## Enable the prctl() interface to prevent leaks from L1D on context switches.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1d_flush.html
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX l1d_flush=on"

## Mitigate numerous MMIO Stale Data vulnerabilities and disable SMT.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/processor_mmio_stale_data.html
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX mmio_stale_data=full,nosmt"

## Enable mitigations for RETBleed (Arbitrary Speculative Code Execution with
## Return Instructions) vulnerability and disable SMT.
##
## https://www.suse.com/support/kb/doc/?id=000020693
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX retbleed=auto,nosmt"

## Control RAS overflow mitigation on AMD Zen CPUs.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/srso.html
##
## The default kernel setting will be utilized until provided sufficient evidence to modify.
##
#GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX spec_rstack_overflow=safe-ret"

## Enable Gather Data Sampling (GDS) mitigation.
## Note for systems that have not received a suitable microcode update this will
## entirely disable use of the AVX instructions set.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/gather_data_sampling.html
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX gather_data_sampling=force"

## Enable Register File Data Sampling (RFDS) mitigation on Intel Atom CPUs which
## encompasses E-cores on hybrid architectures.
##
## https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/reg-file-data-sampling.html
##
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX reg_file_data_sampling=on"