certs: Add ability to preload revocation certs

Add a new Kconfig option called SYSTEM_REVOCATION_KEYS. If set,
this option should be the filename of a PEM-formated file containing
X.509 certificates to be included in the default blacklist keyring.

DH Changes:
 - Make the new Kconfig option depend on SYSTEM_REVOCATION_LIST.
 - Fix SYSTEM_REVOCATION_KEYS=n, but CONFIG_SYSTEM_REVOCATION_LIST=y[1][2].
 - Use CONFIG_SYSTEM_REVOCATION_LIST for extract-cert[3].
 - Use CONFIG_SYSTEM_REVOCATION_LIST for revocation_certificates.o[3].

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Randy Dunlap <rdunlap@infradead.org>
cc: keyrings@vger.kernel.org
Link: https://lore.kernel.org/r/e1c15c74-82ce-3a69-44de-a33af9b320ea@infradead.org/ [1]
Link: https://lore.kernel.org/r/20210303034418.106762-1-eric.snowberg@oracle.com/ [2]
Link: https://lore.kernel.org/r/20210304175030.184131-1-eric.snowberg@oracle.com/ [3]
Link: https://lore.kernel.org/r/20200930201508.35113-3-eric.snowberg@oracle.com/
Link: https://lore.kernel.org/r/20210122181054.32635-4-eric.snowberg@oracle.com/ # v5
Link: https://lore.kernel.org/r/161428673564.677100.4112098280028451629.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/161433312452.902181.4146169951896577982.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/161529606657.163428.3340689182456495390.stgit@warthog.procyon.org.uk/ # v3

certs/Kconfig

@@ -92,4 +92,12 @@ config SYSTEM_REVOCATION_LIST
 	  blacklist keyring and implements a hook whereby a PKCS#7 message can
 	  be checked to see if it matches such a certificate.
 
+config SYSTEM_REVOCATION_KEYS
+	string "X.509 certificates to be preloaded into the system blacklist keyring"
+	depends on SYSTEM_REVOCATION_LIST
+	help
+	  If set, this option should be the filename of a PEM-formatted file
+	  containing X.509 certificates to be included in the default blacklist
+	  keyring.
+
 endmenu

certs/Makefile

@@ -4,7 +4,8 @@
 #
 
 obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o common.o
-obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist.o
+obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist.o common.o
+obj-$(CONFIG_SYSTEM_REVOCATION_LIST) += revocation_certificates.o
 ifneq ($(CONFIG_SYSTEM_BLACKLIST_HASH_LIST),"")
 obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist_hashes.o
 else
@@ -29,7 +30,7 @@ $(obj)/x509_certificate_list: scripts/extract-cert $(SYSTEM_TRUSTED_KEYS_SRCPREF
 	$(call if_changed,extract_certs,$(SYSTEM_TRUSTED_KEYS_SRCPREFIX)$(CONFIG_SYSTEM_TRUSTED_KEYS))
 endif # CONFIG_SYSTEM_TRUSTED_KEYRING
 
-clean-files := x509_certificate_list .x509.list
+clean-files := x509_certificate_list .x509.list x509_revocation_list
 
 ifeq ($(CONFIG_MODULE_SIG),y)
 ###############################################################################
@@ -104,3 +105,17 @@ targets += signing_key.x509
 $(obj)/signing_key.x509: scripts/extract-cert $(X509_DEP) FORCE
 	$(call if_changed,extract_certs,$(MODULE_SIG_KEY_SRCPREFIX)$(CONFIG_MODULE_SIG_KEY))
 endif # CONFIG_MODULE_SIG
+
+ifeq ($(CONFIG_SYSTEM_REVOCATION_LIST),y)
+
+$(eval $(call config_filename,SYSTEM_REVOCATION_KEYS))
+
+$(obj)/revocation_certificates.o: $(obj)/x509_revocation_list
+
+quiet_cmd_extract_certs  = EXTRACT_CERTS   $(patsubst "%",%,$(2))
+      cmd_extract_certs  = scripts/extract-cert $(2) $@
+
+targets += x509_revocation_list
+$(obj)/x509_revocation_list: scripts/extract-cert $(SYSTEM_REVOCATION_KEYS_SRCPREFIX)$(SYSTEM_REVOCATION_KEYS_FILENAME) FORCE
+	$(call if_changed,extract_certs,$(SYSTEM_REVOCATION_KEYS_SRCPREFIX)$(CONFIG_SYSTEM_REVOCATION_KEYS))
+endif

certs/blacklist.c

@@ -17,9 +17,15 @@
 #include <linux/uidgid.h>
 #include <keys/system_keyring.h>
 #include "blacklist.h"
+#include "common.h"
 
 static struct key *blacklist_keyring;
 
+#ifdef CONFIG_SYSTEM_REVOCATION_LIST
+extern __initconst const u8 revocation_certificate_list[];
+extern __initconst const unsigned long revocation_certificate_list_size;
+#endif
+
 /*
  * The description must be a type prefix, a colon and then an even number of
  * hex digits.  The hash is kept in the description.
@@ -220,3 +226,18 @@ static int __init blacklist_init(void)
  * Must be initialised before we try and load the keys into the keyring.
  */
 device_initcall(blacklist_init);
+
+#ifdef CONFIG_SYSTEM_REVOCATION_LIST
+/*
+ * Load the compiled-in list of revocation X.509 certificates.
+ */
+static __init int load_revocation_certificate_list(void)
+{
+	if (revocation_certificate_list_size)
+		pr_notice("Loading compiled-in revocation X.509 certificates\n");
+
+	return load_certificate_list(revocation_certificate_list, revocation_certificate_list_size,
+				     blacklist_keyring);
+}
+late_initcall(load_revocation_certificate_list);
+#endif

certs/revocation_certificates.S

@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/export.h>
+#include <linux/init.h>
+
+	__INITRODATA
+
+	.align 8
+	.globl revocation_certificate_list
+revocation_certificate_list:
+__revocation_list_start:
+	.incbin "certs/x509_revocation_list"
+__revocation_list_end:
+
+	.align 8
+	.globl revocation_certificate_list_size
+revocation_certificate_list_size:
+#ifdef CONFIG_64BIT
+	.quad __revocation_list_end - __revocation_list_start
+#else
+	.long __revocation_list_end - __revocation_list_start
+#endif

scripts/Makefile

@@ -11,6 +11,7 @@ hostprogs-always-$(CONFIG_ASN1)				+= asn1_compiler
 hostprogs-always-$(CONFIG_MODULE_SIG_FORMAT)		+= sign-file
 hostprogs-always-$(CONFIG_SYSTEM_TRUSTED_KEYRING)	+= extract-cert
 hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)	+= insert-sys-cert
+hostprogs-always-$(CONFIG_SYSTEM_REVOCATION_LIST)	+= extract-cert
 
 HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include
 HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include