linux_kernel/certs/Makefile

#
# Makefile for the linux kernel signature checking certificates.
#

obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o

ifeq ($(CONFIG_SYSTEM_TRUSTED_KEYRING),y)

$(eval $(call config_filename,SYSTEM_TRUSTED_KEYS))

# GCC doesn't include .incbin files in -MD generated dependencies (PR#66871)
$(obj)/system_certificates.o: $(obj)/x509_certificate_list

# Cope with signing_key.x509 existing in $(srctree) not $(objtree)
AFLAGS_system_certificates.o := -I$(srctree)

quiet_cmd_extract_certs  = EXTRACT_CERTS   $(patsubst "%",%,$(2))
      cmd_extract_certs  = scripts/extract-cert $(2) $@ || ( rm $@; exit 1)

targets += x509_certificate_list
$(obj)/x509_certificate_list: scripts/extract-cert $(SYSTEM_TRUSTED_KEYS_SRCPREFIX)$(SYSTEM_TRUSTED_KEYS_FILENAME) FORCE
	$(call if_changed,extract_certs,$(SYSTEM_TRUSTED_KEYS_SRCPREFIX)$(CONFIG_SYSTEM_TRUSTED_KEYS))
endif

clean-files := x509_certificate_list .x509.list

ifeq ($(CONFIG_MODULE_SIG),y)
###############################################################################
#
# If module signing is requested, say by allyesconfig, but a key has not been
# supplied, then one will need to be generated to make sure the build does not
# fail and that the kernel may be used afterwards.
#
###############################################################################
ifndef CONFIG_MODULE_SIG_HASH
$(error Could not determine digest type to use from kernel config)
endif

# We do it this way rather than having a boolean option for enabling an
# external private key, because 'make randconfig' might enable such a
# boolean option and we unfortunately can't make it depend on !RANDCONFIG.
ifeq ($(CONFIG_MODULE_SIG_KEY),"certs/signing_key.pem")
$(obj)/signing_key.pem: $(obj)/x509.genkey
	@echo "###"
	@echo "### Now generating an X.509 key pair to be used for signing modules."
	@echo "###"
	@echo "### If this takes a long time, you might wish to run rngd in the"
	@echo "### background to keep the supply of entropy topped up.  It"
	@echo "### needs to be run as root, and uses a hardware random"
	@echo "### number generator if one is available."
	@echo "###"
	openssl req -new -nodes -utf8 -$(CONFIG_MODULE_SIG_HASH) -days 36500 \
		-batch -x509 -config $(obj)/x509.genkey \
		-outform PEM -out $(obj)/signing_key.pem \
		-keyout $(obj)/signing_key.pem 2>&1
	@echo "###"
	@echo "### Key pair generated."
	@echo "###"

$(obj)/x509.genkey:
	@echo Generating X.509 key generation config
	@echo  >$@ "[ req ]"
	@echo >>$@ "default_bits = 4096"
	@echo >>$@ "distinguished_name = req_distinguished_name"
	@echo >>$@ "prompt = no"
	@echo >>$@ "string_mask = utf8only"
	@echo >>$@ "x509_extensions = myexts"
	@echo >>$@
	@echo >>$@ "[ req_distinguished_name ]"
	@echo >>$@ "#O = Unspecified company"
	@echo >>$@ "CN = Build time autogenerated kernel key"
	@echo >>$@ "#emailAddress = unspecified.user@unspecified.company"
	@echo >>$@
	@echo >>$@ "[ myexts ]"
	@echo >>$@ "basicConstraints=critical,CA:FALSE"
	@echo >>$@ "keyUsage=digitalSignature"
	@echo >>$@ "subjectKeyIdentifier=hash"
	@echo >>$@ "authorityKeyIdentifier=keyid"
endif

$(eval $(call config_filename,MODULE_SIG_KEY))

# If CONFIG_MODULE_SIG_KEY isn't a PKCS#11 URI, depend on it
ifeq ($(patsubst pkcs11:%,%,$(firstword $(MODULE_SIG_KEY_FILENAME))),$(firstword $(MODULE_SIG_KEY_FILENAME)))
X509_DEP := $(MODULE_SIG_KEY_SRCPREFIX)$(MODULE_SIG_KEY_FILENAME)
endif

# GCC PR#66871 again.
$(obj)/system_certificates.o: $(obj)/signing_key.x509

targets += signing_key.x509
$(obj)/signing_key.x509: scripts/extract-cert $(X509_DEP) FORCE
	$(call if_changed,extract_certs,$(MODULE_SIG_KEY_SRCPREFIX)$(CONFIG_MODULE_SIG_KEY))
endif