V8.00.000.2025.06.17

Signed-off-by: Marc S. Weidner <msw@coresecret.dev>

func/4160_grub_bootparameter.sh

@@ -0,0 +1,361 @@
+#!/bin/bash
+# SPDX-Version: 3.0
+# SPDX-CreationInfo: 2025-06-17; WEIDNER, Marc S.; <msw@coresecret.dev>
+# SPDX-ExternalRef: GIT https://git.coresecret.dev/msw/CISS.debian.installer.git
+# SPDX-FileContributor: WEIDNER, Marc S.; Centurion Intelligence Consulting Agency
+# SPDX-FileCopyrightText: 2024-2025; WEIDNER, Marc S.; <msw@coresecret.dev>
+# SPDX-FileType: SOURCE
+# SPDX-License-Identifier: EUPL-1.2 OR LicenseRef-CCLA-1.0
+# SPDX-LicenseComment: This file is part of the CISS.debian.installer.secure framework.
+# SPDX-PackageName: CISS.debian.installer
+# SPDX-Security-Contact: security@coresecret.eu
+
+guard_sourcing
+
+#######################################
+# Hardening Grub boot parameter.
+# Globals:
+#   TARGET
+#   VAR_GRUB_CMDLINE_LINUX
+#   VAR_SETUP_PATH
+# Arguments:
+#   None
+# Returns:
+#   0: Successfully executed commands.
+#######################################
+setup_grub_bootparameter() {
+  ### Install Kernel Hardening-Presets
+  cp "${VAR_SETUP_PATH}/includes/etc/sysctl.d/99_local.hardened" "${TARGET}/etc/sysctl.d/99_local.hardened"
+  chmod 0644 "${TARGET}/etc/sysctl.d/99_local.hardened"
+
+  ### Entropy collection improvements
+  mkdir -p "${TARGET}/usr/lib/modules-load.d"
+  cat << EOF >| "${TARGET}/usr/lib/modules-load.d/30_security-misc.conf"
+## https://www.whonix.org/wiki/Dev/Entropy
+## https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=927972
+## https://forums.whonix.org/t/jitterentropy-rngd/7204
+jitterentropy_rng
+EOF
+  chmod 0644 "${TARGET}/usr/lib/modules-load.d/30_security-misc.conf"
+
+  grub_extract_current_string
+
+  ###########################################################################################
+  # Audit events need to be captured on processes that start up prior to auditd,            #
+  # so that potential malicious activity cannot go undetected. During boot if audit=1, then #
+  # the backlog will hold 64 records. If more than 64 records are created during boot,      #
+  # auditd records will be lost and potential malicious activity could go undetected        #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} audit=1 audit_backlog_limit=8192"
+
+  ###########################################################################################
+  # Distrusts CPU bootloader for initial entropy at boot.                                   #
+  # Distrusts the CPU for initial entropy at boot, as it is not possible to audit,          #
+  # may contain weaknesses or a backdoor.                                                   #
+  ###########################################################################################
+  # https://en.wikipedia.org/wiki/RDRAND#Reception                                          #
+  # https://twitter.com/pid_eins/status/1149649806056280069                                 #
+  # https://archive.nytimes.com/www.nytimes.com/interactive/2013/09/05/us/documents-reveal-nsa-campaign-against-encryption.html
+  # https://forums.whonix.org/t/entropy-config-random-trust-cpu-yes-or-no-rng-core-default-quality/8566
+  # https://lkml.org/lkml/2022/6/5/271                                                      #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} random.trust_cpu=off"
+
+  ###########################################################################################
+  # Distrusts the bootloader for initial entropy at boot.                                   #
+  # https://lkml.org/lkml/2022/6/5/271                                                      #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} random.trust_bootloader=off"
+
+  ###########################################################################################
+  # ASLR (Address Space Layout Randomization) causes central areas of memory to be assigned #
+  # random addresses each time a program is started. These include: Stack, Heap, Shared     #
+  # libraries (e.g., libc), mmap regions, VDSO/VSyscall. The executable itself (only with   #
+  # PIE binaries). The aim is to make it more difficult for attackers to predict memory     #
+  # addresses, thereby preventing classic exploits that rely on known addresses from        #
+  # succeeding.                                                                             #
+  # 0: disabled Fixed memory addresses – insecure, testable.                                #
+  # 1: Partial ASLR Heap, mmap are randomized, stack only partially randomized.             #
+  # 2: Full ASLR (default) Stack, mmap, heap, VDSO, shared libraries all randomized.        #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} randomize_va_space=2"
+
+  ###########################################################################################
+  # Enables IOMMU to prevent DMA attacks.                                                   #
+  # intel_iommu=on amd_iommu=force_isolation iommu=force                                    #
+  # Multiple IOMMU switches are redundant; iommu=force is usually sufficient.               #
+  # Forces an IOMMU to be initialized and used completely, even if the BIOS or ACPI wanted  #
+  # to disable it. It activates the basic DMA remapping function. However, it does not say  #
+  # anything about how restrictive the mapping strategy is, passthrough, strict, see below  #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} iommu=force"
+
+  ###########################################################################################
+  # Enables strict enforcement of IOMMU TLB invalidation, so devices will never be able to  #
+  # access stale data contents.                                                             #
+  # iommu.passthrough=0                                                                     #
+  # Prevents devices from operating in identity-mapped passthrough mode. Without this       #
+  # parameter (or with =1), devices could be passed through without being monitored by the  #
+  # IOMMU in a truly restrictive manner. From a security standpoint, iommu.passthrough=0 is #
+  # an important step toward DMA isolation for all devices, especially for untrusted PCI(e) #
+  # devices.                                                                                #
+  # iommu.strict=1                                                                          #
+  # Enables Strict Mode for dma-iommu.c (i.e., all DMA transactions are validated           #
+  # synchronously). Without this parameter, the kernel often runs in lazy mode, where       #
+  # mapping caches are used.                                                                #
+  # Performance vs. security: strict=1= more secure, but potentially slower, especially     #
+  # with many small DMA transfers.                                                          #
+  # https://github.com/torvalds/linux/blob/master/drivers/iommu/Kconfig#L97                 #
+  # Page 11 of https://lenovopress.lenovo.com/lp1467.pdf                                    #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} iommu.passthrough=0 iommu.strict=1"
+
+  ###########################################################################################
+  # Disable the busmaster bit on all PCI bridges during very early boot to avoid holes in   #
+  # IOMMU.                                                                                  #
+  # https://mjg59.dreamwidth.org/54433.html                                                 #
+  # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4444f8541dad16fefd9b8807ad1451e806ef1d94
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} efi=disable_early_pci_dma"
+
+  ###########################################################################################
+  # Disables the merging of slabs of similar sizes.                                         #
+  # Sometimes a slab can be used vulnerably, which an attacker can exploit.                 #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} slab_nomerge"
+
+  ###########################################################################################
+  # Zero memory at allocation and free time.                                                #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} init_on_alloc=1 init_on_free=1"
+
+  ###########################################################################################
+  # This option randomizes page allocator freelists, improving security by making page      #
+  # allocations less predictable. This also improves performance.                           #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} page_alloc.shuffle=1"
+
+  ###########################################################################################
+  # When releasing (i.e., free_pages()), all bytes with a marker value (e.g., 0xAA) are     #
+  # overwritten. If later code (accidentally or maliciously) accesses this page, it will    #
+  # most likely crash or produce recognizable artifacts. Only supported if the kernel was   #
+  # built with CONFIG_PAGE_POISONING=y (default on Debian: enabled since Bookworm).         #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} page_poison=1"
+
+  ###########################################################################################
+  # Enables Kernel Page Table Isolation, which mitigates Meltdown, improves KASLR.          #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} pti=on"
+
+  ###########################################################################################
+  # The setting 'vsyscall' is obsolete, are at fixed addresses and are a target for ROP.    #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} vsyscall=none"
+
+  ###########################################################################################
+  # The kernel adds a small random padding offset to the stack pointer with every system    #
+  # call or kernel entry. The starting point for local variables is at a different position #
+  # within the stack with every call. This makes ROP chains (return-oriented programming)   #
+  # or stack pivoting attacks significantly more difficult.                                 #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} randomize_kstack_offset=on"
+
+  ###########################################################################################
+  # Prevents the debugfsfile system from being made available at boot time. This is a       #
+  # useful hardening measure because debugfs reveals a lot of potentially security-relevant #
+  # kernel information by default, which can be misused by normal users (and  by exploits). #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} debugfs=off"
+
+  ###########################################################################################
+  # Force the kernel to panic on "oopses" (which may be due to false positives).            #
+  # panic=N (e.g., panic=60): Wait N seconds and then reboot.                               #
+  # panic=0 No automatic action (System remains stuck in panic state).                      #
+  # panic=-1 Also explicitly prevents any automatic reboot.                                 #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} oops=panic panic=-1"
+
+  ###########################################################################################
+  # Enable a subset of known mitigations for CPU vulnerabilities and disable SMT.           #
+  # mitigations=auto Enables all available CPU-specific security measures based on the      #
+  # detected CPU, microcode version, and kernel build configuration, if applicable.         #
+  # 'nosmt' Disables Simultaneous Multithreading (SMT) (e.g., Hyper-Threading on Intel)     #
+  # system-wide to prevent shared cache attacks (SMoTHER, MDS, L1TF, TAA, Snoop-assisted).  #
+  # Why is 'mitigations=auto,nosmt' better than setting everything manually?                #
+  # Automatically adjusted: Depending on CPU family, stepping, microcode.                   #
+  # Consistency guaranteed: No contradictions between flags possible                        #
+  # (e.g., spec_store_bypass_disable=on vs. nospec_store_bypass_disable=off).               #
+  # Future-proof: Even new kernel features (e.g., bhi=flush or srbds) are automatically     #
+  # activated without having to know about them.                                            #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} mitigations=auto,nosmt"
+
+  ###########################################################################################
+  # If mitigations=auto,nosmt is set, see before, then these flags should not be set        #
+  # individually because they are redundant. Enable mitigations for both Spectre Variant 2  #
+  # (indirect branch speculation) and Intel branch history injection (BHI) vulnerabilities. #
+  # https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/spectre.html                 #
+  ###########################################################################################
+  # VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} spectre_v2=on spectre_v2_user=on spectre_bhi=on"
+
+  ###########################################################################################
+  # If mitigations=auto,nosmt is set, see before, then these flags should not be set        #
+  # individually because they are redundant.                                                #
+  # Disable Speculative Store Bypass (Spectre Variant 4).                                   #
+  # https://www.suse.com/support/kb/doc/?id=000019189                                       #
+  ###########################################################################################
+  # VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} spec_store_bypass_disable=on nospec_store_bypass_disable=off"
+
+  ###########################################################################################
+  # If mitigations=auto,nosmt is set, see before, then these flags should not be set        #
+  # individually because they are redundant.                                                #
+  # Enable mitigations for the L1TF vulnerability through disabling SMT and L1D flush       #
+  # runtime control.                                                                        #
+  # https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html                    #
+  ###########################################################################################
+  # VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} l1tf=full,force"
+
+  ###########################################################################################
+  # If mitigations=auto,nosmt is set, see before, then these flags should not be set        #
+  # individually because they are redundant.                                                #
+  # 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                     #
+  ###########################################################################################
+  # VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} mds=full,nosmt"
+
+  ###########################################################################################
+  # If mitigations=auto,nosmt is set, see before, then these flags should not be set        #
+  # individually because they are redundant.                                                #
+  # Patches the TAA vulnerability by disabling TSX and enables mitigations using TSX Async  #
+  # Abort along with disabling SMT.                                                         #
+  # https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html         #
+  ###########################################################################################
+  # VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} tsx=off 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                #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} kvm.nx_huge_pages=force"
+
+  ###########################################################################################
+  # Force disable SMT as it has caused numerous CPU vulnerabilities.                        #
+  # The only full mitigation of cross-HT attacks is to disable SMT.                         #
+  # https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/core-scheduling.html         #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} nosmt=force"
+
+  ###########################################################################################
+  # Enables 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               #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} l1d_flush=on"
+
+  ###########################################################################################
+  # Mitigates numerous MMIO Stale Data vulnerabilities and disables SMT.                    #
+  # mmio_stale_data=off        No mitigation (unsafe)                                       #
+  # mmio_stale_data=full       All known measures active                                    #
+  # mmio_stale_data=full,nosmt Full mitigation + SMT disabling                              #
+  # mmio_stale_data=auto       Activated depending on CPU/microcode                         #
+  # mmio_stale_data=full,force Forces mitigation even on CPUs that are supposedly not       #
+  #                            affected                                                     #
+  # https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/processor_mmio_stale_data.html
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} mmio_stale_data=full,force"
+
+  ###########################################################################################
+  # Enable mitigations for RETBleed (Arbitrary Speculative Code Execution with              #
+  # Return Instructions) vulnerability and disable SMT.                                     #
+  # If 'mitigations=auto,nosmt' is set, the kernel already activates all retbleed-relevant  #
+  # mitigations, provided the CPU is affected; 'retbleed=auto,nosmt' explicitly overrides   #
+  # the internal assessment and forces full protection. If maximum hardening is required,   #
+  # and one does not want to rely on "auto-detection" then it is recommended to additionally#
+  # set 'retbleed=auto,nosmt' otherwise, 'mitigations=auto,nosmt' is sufficient.            #
+  # https://www.suse.com/support/kb/doc/?id=000020693                                       #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} retbleed=auto"
+
+  ###########################################################################################
+  # Enables kernel lockdown mode with a focus on confidentiality. The kernel is             #
+  # configured in such a way that even privileged users (such as root) have limited access  #
+  # to  kernel data and debug mechanisms. 'confidentiality': Maximum restriction to ensure  #
+  # the security and integrity of the system. This prevents direct access to hardware and   #
+  # debug interfaces, for example. Useful for highly secure environments as it reduces the  #
+  # attack surface to kernel data. However, some applications that require debugging or     #
+  # hardware access may have problems.                                                      #
+  # https://blog.cloudflare.com/de-de/linux-kernel-hardening/                               #
+  # https://www.linux-magazine.com/Issues/2020/239/Lockdown-Mode                            #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} lockdown=confidentiality"
+
+  ###########################################################################################
+  # Enables 'Read-Only Data Protection', which implements read-only memory areas            #
+  # for kernel data structures. This protects the kernel from certain types of exploit      #
+  # (e.g., buffer overflows). 'on': Forces the corresponding areas to remain read-only.     #
+  # https://www.kernel.org/doc/html/v6.10/admin-guide/kernel-parameters.html                #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} rodata=on"
+
+  ###########################################################################################
+  # Kernel Electric-Fence (KFENCE) is a low-overhead sampling-based memory safety           #
+  # error detector. KFENCE detects heap out-of-bounds access, use-after-free, and           #
+  # invalid-free errors. KFENCE is designed to be enabled in production kernels, and has    #
+  # near zero performance overhead. Compared to KASAN, KFENCE trades performance for        #
+  # precision. The main motivation behind KFENCE’s design is that with enough total uptime  #
+  # KFENCE will detect bugs in code paths not typically exercised by non-production test    #
+  # workloads. One way to quickly achieve a large enough total uptime is when the tool is   #
+  # deployed across a large fleet of machines.                                              #
+  # https://docs.kernel.org/dev-tools/kfence.html                                           #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} kfence.sample_interval=100"
+
+  ###########################################################################################
+  # CFI Ensures that only controlled, predefined transitions are possible in the            #
+  # programs' control flow. kcfi (Kernel Control Flow Integrity): Specific implementation of#
+  # CFI for the Linux kernel that is particularly robust and provides accurate control flow #
+  # validation. kcfi relies on compiler-based technologies (e.g., LLVM) that insert special #
+  # checks and instrumentation into the kernel code.                                        #
+  # https://kspp.github.io/Recommended_Settings#kernel-command-line-options                 #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} cfi=kcfi"
+
+  ###########################################################################################
+  # Remove additional (32-bit) attack surface, unless you really need them.                 #
+  # https://www.kernel.org/doc/html/v6.10/admin-guide/kernel-parameters.html                #
+  # https://kspp.github.io/Recommended_Settings#kernel-command-line-options                 #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} ia32_emulation=0"
+
+  ###########################################################################################
+  # Removes mapping for 32-bit VDSO (for ia32binaries). On 32-bit processes that rely on    #
+  # VDSO, this causes a fallback to classic syscalls (slower) or errors. On a system        #
+  # without CONFIG_IA32_EMULATION or with ia32_emulation=0, vdso32=0 is effective but       #
+  # redundant.                                                                              #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} vdso32=0"
+
+  ###########################################################################################
+  # Checks every copy_to_user() / copy_from_user()operation. Prevents kernels from          #
+  # accidentally copying unallocated memory to userspace. Stop exploits that trigger        #
+  # buffer overflows or use-after-free via copy_*_user(), for example. Effect: Detects      #
+  # heap/SLOB abuse, overwrites. Leads to BUG() & stack trace if suspicious access is       #
+  # detected.                                                                               #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} hardened_usercopy=1"
+
+  ###########################################################################################
+  # Sets the minimum log output of the kernel at boot time to level 0 (= KERN_EMERG).       #
+  ###########################################################################################
+  VAR_GRUB_CMDLINE_LINUX="${VAR_GRUB_CMDLINE_LINUX} loglevel=0"
+
+  grub_finalize_string
+
+  do_in_target "${TARGET}" update-grub
+
+  do_log "info" "true" "Setting GRUB kernel parameters: ${VAR_GRUB_CMDLINE_LINUX}"
+
+  return 0
+}
+# vim: number et ts=2 sw=2 sts=2 ai tw=128 ft=sh

func/4170_installation_microcode.sh

@@ -0,0 +1,55 @@
+#!/bin/bash
+# SPDX-Version: 3.0
+# SPDX-CreationInfo: 2025-06-17; WEIDNER, Marc S.; <msw@coresecret.dev>
+# SPDX-ExternalRef: GIT https://git.coresecret.dev/msw/CISS.debian.installer.git
+# SPDX-FileContributor: WEIDNER, Marc S.; Centurion Intelligence Consulting Agency
+# SPDX-FileCopyrightText: 2024-2025; WEIDNER, Marc S.; <msw@coresecret.dev>
+# SPDX-FileType: SOURCE
+# SPDX-License-Identifier: EUPL-1.2 OR LicenseRef-CCLA-1.0
+# SPDX-LicenseComment: This file is part of the CISS.debian.installer.secure framework.
+# SPDX-PackageName: CISS.debian.installer
+# SPDX-Security-Contact: security@coresecret.eu
+
+guard_sourcing
+
+#######################################
+# Install microcode updates depending on architecture (amd64, arm64, intel64) and environment (Baremetal, VM)
+# Globals:
+#   TARGET
+# Arguments:
+#   None
+# Returns:
+#   0: Successfully executed commands.
+#######################################
+installation_microcode() {
+  declare var_microcode_pkgs=""
+
+  declare var_whereiam; var_whereiam=$(virt-what | head -n1)
+  [[ -z "${var_whereiam}" ]] && var_whereiam="baremetal"
+
+  declare var_cpu_vendor; var_cpu_vendor=$(lscpu | awk -F: '/Vendor ID/ {print $2}' | xargs)
+
+  case "${var_cpu_vendor}" in
+    *AuthenticAMD*)   var_microcode_pkgs="amd64-microcode" ;;
+    *GenuineIntel*)   var_microcode_pkgs="intel-microcode" ;;
+    ""|*ARM*|*arm*|*) var_microcode_pkgs=""; do_log "info" "true" "ARM or unknown CPU detected – skipping microcode install" ;;
+  esac
+
+  ###########################################################################################
+  # Generally, it is best to let the hypervisor handle CPU microcode updates.               #
+  ###########################################################################################
+  if [[ "${var_whereiam}" != "kvm" && -n "${var_microcode_pkgs}" ]]; then
+
+    if ! do_in_target "${TARGET}" dpkg -l "${var_microcode_pkgs}" >/dev/null 2>&1; then
+      do_in_target "${TARGET}" apt-get install -y "${var_microcode_pkgs}"
+    fi
+
+  else
+
+    do_log "info" "true" "Skipping microcode install (${var_whereiam}, ${var_microcode_pkgs:-none})"
+
+  fi
+
+  return 0
+}
+# vim: number et ts=2 sw=2 sts=2 ai tw=128 ft=sh