keys: define build time generated ephemeral kernel CA key

Certificates being loaded onto the IMA trusted keyring must be signed by
a key on either the builtin and secondary trusted keyring.

This patch creates and includes in the kernel image an ephemeral CA
key, at build time when IMA_APPRAISE_MODSIG is enabled.

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>

Makefile

@@ -1481,6 +1481,8 @@ MRPROPER_FILES += include/config include/generated          \
 		  certs/signing_key.pem certs/signing_key.x509 \
 		  certs/x509.genkey certs/signing_key.key \
 		  certs/signing_key.crt certs/signing_key.csr \
+		  certs/ca_signing_key.pem certs/ca_signing_key.x509 \
+		  certs/ca_signing_key.srl \
 		  vmlinux-gdb.py \
 		  *.spec
 

certs/Makefile

@@ -32,6 +32,14 @@ endif # CONFIG_SYSTEM_TRUSTED_KEYRING
 clean-files := x509_certificate_list .x509.list
 
 ifeq ($(CONFIG_MODULE_SIG),y)
+SIGN_KEY = y
+endif
+
+ifeq ($(CONFIG_IMA_APPRAISE_MODSIG),y)
+SIGN_KEY = y
+endif
+
+ifdef SIGN_KEY
 ###############################################################################
 #
 # If module signing is requested, say by allyesconfig, but a key has not been
@@ -51,6 +59,16 @@ silent_redirect_openssl = 2>/dev/null
 # external private key, because 'make randconfig' might enable such a
 # boolean option and we unfortunately can't make it depend on !RANDCONFIG.
 ifeq ($(CONFIG_MODULE_SIG_KEY),"certs/signing_key.pem")
+
+ifeq ($(CONFIG_IMA_APPRAISE_MODSIG),y)
+# openssl arguments for CA Signed certificate.
+CA_KEY = certs/ca_signing_key.pem
+SIGNER = -CA $(CA_KEY) -CAkey $(CA_KEY) -CAcreateserial
+else
+# openssl arguments for Self Signed certificate.
+SIGNER = -signkey $(obj)/signing_key.key
+endif # CONFIG_IMA_APPRAISE_MODSIG
+
 $(obj)/signing_key.pem: $(obj)/x509.genkey
 	@$(kecho) "###"
 	@$(kecho) "### Now generating an X.509 key pair to be used for signing modules."
@@ -60,14 +78,23 @@ $(obj)/signing_key.pem: $(obj)/x509.genkey
 	@$(kecho) "### needs to be run as root, and uses a hardware random"
 	@$(kecho) "### number generator if one is available."
 	@$(kecho) "###"
+ifeq ($(CONFIG_IMA_APPRAISE_MODSIG),y)
+	# Generate kernel build time CA Certificate.
+	@$(Q)openssl req -new -nodes -utf8 \
+		-$(CONFIG_MODULE_SIG_HASH) -days 36500 \
+		-subj "/CN=Build time autogenerated kernel CA key" \
+		-batch -x509 -config $(obj)/x509.genkey \
+		-outform PEM -out $(CA_KEY) \
+		-keyout $(CA_KEY) -extensions ca_ext \
+		$($(quiet)redirect_openssl)
+endif # CONFIG_IMA_APPRAISE_MODSIG
 	$(Q)openssl req -new -nodes -utf8 \
 		-batch -config $(obj)/x509.genkey \
 		-outform PEM -out $(obj)/signing_key.csr \
 		-keyout $(obj)/signing_key.key -extensions myexts \
 		$($(quiet)redirect_openssl)
 	$(Q)openssl x509 -req -days 36500 -in $(obj)/signing_key.csr \
-		-outform PEM -out $(obj)/signing_key.crt \
-		-signkey $(obj)/signing_key.key \
+		-outform PEM -out $(obj)/signing_key.crt $(SIGNER) \
 		-$(CONFIG_MODULE_SIG_HASH) -extensions myexts \
 		-extfile $(obj)/x509.genkey \
 		$($(quiet)redirect_openssl)
@@ -95,19 +122,50 @@ $(obj)/x509.genkey:
 	@echo >>$@ "keyUsage=digitalSignature"
 	@echo >>$@ "subjectKeyIdentifier=hash"
 	@echo >>$@ "authorityKeyIdentifier=keyid"
+	@echo >>$@
+	@echo >>$@ "[ ca_ext ]"
+	@echo >>$@ "keyUsage=critical,keyCertSign"
+	@echo >>$@ "basicConstraints=critical,CA:TRUE,pathlen:0"
+	@echo >>$@ "subjectKeyIdentifier=hash"
+	@echo >>$@ "authorityKeyIdentifier=keyid"
 endif # CONFIG_MODULE_SIG_KEY
 
 $(eval $(call config_filename,MODULE_SIG_KEY))
+SUBJECT=CN = Build time autogenerated kernel key
+ISSUER=$(shell openssl x509 -in certs/signing_key.crt -noout -issuer)
 
 # If CONFIG_MODULE_SIG_KEY isn't a PKCS#11 URI, depend on it
+
+# GCC PR#66871 again.
+ifeq ($(CONFIG_IMA_APPRAISE_MODSIG),y)
+
+# Remove existing keys if it is self-signed.
+$(if $(findstring $(SUBJECT),$(ISSUER)),$(shell rm -f certs/signing_key.* certs/x509.genkey))
+CA_KEY = certs/ca_signing_key.pem
+
+$(obj)/system_certificates.o: $(obj)/ca_signing_key.x509 $(obj)/signing_key.x509
+
+targets += ca_signing_key.x509
+$(obj)/ca_signing_key.x509: $(obj)/signing_key.x509 scripts/extract-cert FORCE
+	$(call if_changed,extract_certs,$(CA_KEY))
+
+targets += signing_key.x509
+$(obj)/signing_key.x509: $(obj)/signing_key.pem scripts/extract-cert FORCE
+	$(call if_changed,extract_certs,$(MODULE_SIG_KEY_SRCPREFIX)$(CONFIG_MODULE_SIG_KEY))
+else
+
+# Remove existing keys if it is CA signed.
+$(if $(findstring $(SUBJECT),$(ISSUER)),,$(shell rm -f certs/ca_signing_key.* certs/signing_key.* certs/x509.genkey))
+
 ifeq ($(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 $(X509_DEP) FORCE
+$(obj)/signing_key.x509: certs/signing_key.pem scripts/extract-cert $(X509_DEP) FORCE
 	$(call if_changed,extract_certs,$(MODULE_SIG_KEY_SRCPREFIX)$(CONFIG_MODULE_SIG_KEY))
-endif # CONFIG_MODULE_SIG
+
+endif # CONFIG_IMA_APPRAISE_MODSIG
+endif # SIGN_KEY

certs/system_certificates.S

@@ -8,8 +8,13 @@
 	.globl system_certificate_list
 system_certificate_list:
 __cert_list_start:
-#ifdef CONFIG_MODULE_SIG
+__module_cert_start:
+#if defined(CONFIG_MODULE_SIG) || defined(CONFIG_IMA_APPRAISE_MODSIG)
 	.incbin "certs/signing_key.x509"
+#endif
+__module_cert_end:
+#ifdef CONFIG_IMA_APPRAISE_MODSIG
+	.incbin "certs/ca_signing_key.x509"
 #endif
 	.incbin "certs/x509_certificate_list"
 __cert_list_end:
@@ -35,3 +40,12 @@ system_certificate_list_size:
 #else
 	.long __cert_list_end - __cert_list_start
 #endif
+
+	.align 8
+	.globl module_cert_size
+	module_cert_size:
+#ifdef CONFIG_64BIT
+	.quad __module_cert_end - __module_cert_start
+#else
+	.long __module_cert_end - __module_cert_start
+#endif