Re: [PATCH v2 4/5] keys: define build time generated ephemeral kernel CA key

Stefan Berger <stefanb@xxxxxxxxxxxxx> · Fri, 19 Feb 2021 10:25:38 -0500

On 2/18/21 5:00 PM, Nayna Jain wrote:
Certificates being loaded onto the IMA trusted keyring must be signed by
a key on either the builtin or secondary trusted keyring. Create and
include in the kernel image an ephemeral CA key at build time when
IMA_APPRAISE_MODSIG is enabled.

Reported-by: kernel test robot <lkp@xxxxxxxxx> (redirect openssl stderr)
Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxx>
---
  Makefile                    |  2 ++
  certs/Makefile              | 68 ++++++++++++++++++++++++++++++++++---
  certs/system_certificates.S | 16 ++++++++-
  3 files changed, 80 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index a971d4ae40bd..15e8344836b1 100644
--- a/Makefile
+++ b/Makefile
@@ -1475,6 +1475,8 @@ 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
  
diff --git a/certs/Makefile b/certs/Makefile
index b2be7eb413d3..3fe6b73786fa 100644
--- a/certs/Makefile
+++ b/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 $($(quiet)redirect_openssl))
  
  # 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.

I think you should keep this comment at this place here.


  $(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
diff --git a/certs/system_certificates.S b/certs/system_certificates.S
index 8f29058adf93..e10043800a7e 100644
--- a/certs/system_certificates.S
+++ b/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








