add infrastructure for x86 CPU microcode updates

This change adds the infrastructure to enable early application of CPU
microcodes for the generic-x86_64 platform once the BR2_PACKAGE_INTEL_MICROCODE
or BR2_PACKAGE_LINUX_FIRMWARE_AMD_UCODE options are enabled. Once
enabled a kconfig fragment will be generated which will then dynamically
add CONFIG_EXTRA_FIRMWARE option to the kernel config for embedding all
microcode files accordingly. This should help to get CPU microcode fixes
in place once HAos is directly installed on a x86-64 system using the
generic-x86_64 platform images.

Author: jens-maus

buildroot-external/configs/generic_x86_64_defconfig

@@ -102,6 +102,8 @@ BR2_PACKAGE_LINUX_FIRMWARE_BNX2X=y
 BR2_PACKAGE_LINUX_FIRMWARE_RTL_815X=y
 BR2_PACKAGE_LINUX_FIRMWARE_RTL_8169=y
 BR2_PACKAGE_LINUX_FIRMWARE_USB_SERIAL_TI=y
+BR2_PACKAGE_LINUX_FIRMWARE_AMD_UCODE=y
+BR2_PACKAGE_INTEL_MICROCODE=y
 BR2_PACKAGE_DBUS_BROKER=y
 BR2_PACKAGE_GPTFDISK=y
 BR2_PACKAGE_GPTFDISK_SGDISK=y

buildroot-external/external.mk

@@ -10,3 +10,26 @@ linux-check-dotconfig: linux-check-configuration-done
 		--src-kconfig $(LINUX_SRCDIR)Kconfig \
 		--actual-config $(LINUX_SRCDIR).config \
 		$(shell echo $(BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE) $(BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES))
+
+# if cpu microcode is required we embed it into the kernel build
+ifeq ($(or $(BR2_PACKAGE_INTEL_MICROCODE),$(BR2_PACKAGE_LINUX_FIRMWARE_AMD_UCODE)),y)
+
+UCODE_FRAG := $(BINARIES_DIR)/linux-ucode.fragment
+
+# Hook: Generate fragment before kernel configuration
+define GEN_UCODE_FRAGMENT
+	@echo ">> Generating $(UCODE_FRAG)"
+	@mkdir -p $(BINARIES_DIR)
+	@{ \
+		echo 'CONFIG_EXTRA_FIRMWARE_DIR="$(BINARIES_DIR)"'; \
+		printf 'CONFIG_EXTRA_FIRMWARE="'; \
+		( cd $(BINARIES_DIR) 2>/dev/null && \
+		  find intel-ucode amd-ucode -type f \! -name "*README*" \! -name "*.asc" -printf '%p ' 2>/dev/null || true ); \
+		echo '"'; \
+	} > $(UCODE_FRAG)
+endef
+
+LINUX_PRE_PATCH_HOOKS += GEN_UCODE_FRAGMENT
+LINUX_KCONFIG_FRAGMENT_FILES += $(UCODE_FRAG)
+
+endif

buildroot-external/scripts/rootfs-layer.sh

@@ -39,6 +39,10 @@ function fix_rootfs() {
         find "${TARGET_DIR}/share/locale" -name "grub.mo" -delete
         find "${TARGET_DIR}/share/locale" -type d -empty -delete
     fi
+
+    # Remove unnecessary microcodes in /lib/firmware
+    rm -rf "${TARGET_DIR}/lib/firmware/intel-ucode"
+    rm -rf "${TARGET_DIR}/lib/firmware/amd-ucode"
 }