KEYS: Separate the kernel signature checking keyring from module signing

Separate the kernel signature checking keyring from module signing so that it
can be used by code other than the module-signing code.

Signed-off-by: David Howells <[email protected]>

include/keys/system_keyring.h

@@ -0,0 +1,23 @@
+/* System keyring containing trusted public keys.
+ *
+ * Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([email protected])
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#ifndef _KEYS_SYSTEM_KEYRING_H
+#define _KEYS_SYSTEM_KEYRING_H
+
+#ifdef CONFIG_SYSTEM_TRUSTED_KEYRING
+
+#include <linux/key.h>
+
+extern struct key *system_trusted_keyring;
+
+#endif
+
+#endif /* _KEYS_SYSTEM_KEYRING_H */

init/Kconfig

@@ -1668,6 +1668,18 @@ config BASE_SMALL
 	default 0 if BASE_FULL
 	default 1 if !BASE_FULL
 
+config SYSTEM_TRUSTED_KEYRING
+	bool "Provide system-wide ring of trusted keys"
+	depends on KEYS
+	help
+	  Provide a system keyring to which trusted keys can be added.  Keys in
+	  the keyring are considered to be trusted.  Keys may be added at will
+	  by the kernel from compiled-in data and from hardware key stores, but
+	  userspace may only add extra keys if those keys can be verified by
+	  keys already in the keyring.
+
+	  Keys in this keyring are used by module signature checking.
+
 menuconfig MODULES
 	bool "Enable loadable module support"
 	option modules
@@ -1741,6 +1753,7 @@ config MODULE_SRCVERSION_ALL
 config MODULE_SIG
 	bool "Module signature verification"
 	depends on MODULES
+	select SYSTEM_TRUSTED_KEYRING
 	select KEYS
 	select CRYPTO
 	select ASYMMETRIC_KEY_TYPE

kernel/Makefile

@@ -54,8 +54,9 @@ obj-$(CONFIG_SMP) += spinlock.o
 obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
 obj-$(CONFIG_PROVE_LOCKING) += spinlock.o
 obj-$(CONFIG_UID16) += uid16.o
+obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o
 obj-$(CONFIG_MODULES) += module.o
-obj-$(CONFIG_MODULE_SIG) += module_signing.o modsign_pubkey.o modsign_certificate.o
+obj-$(CONFIG_MODULE_SIG) += module_signing.o
 obj-$(CONFIG_KALLSYMS) += kallsyms.o
 obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
 obj-$(CONFIG_KEXEC) += kexec.o
@@ -141,18 +142,19 @@ targets += timeconst.h
 $(obj)/timeconst.h: $(obj)/hz.bc $(src)/timeconst.bc FORCE
 	$(call if_changed,bc)
 
-ifeq ($(CONFIG_MODULE_SIG),y)
 ###############################################################################
 #
 # Roll all the X.509 certificates that we can find together and pull them into
-# the kernel.
+# the kernel so that they get loaded into the system trusted keyring during
+# boot.
 #
 # We look in the source root and the build root for all files whose name ends
 # in ".x509".  Unfortunately, this will generate duplicate filenames, so we
 # have make canonicalise the pathnames and then sort them to discard the
 # duplicates.
 #
 ###############################################################################
+ifeq ($(CONFIG_SYSTEM_TRUSTED_KEYRING),y)
 X509_CERTIFICATES-y := $(wildcard *.x509) $(wildcard $(srctree)/*.x509)
 X509_CERTIFICATES-$(CONFIG_MODULE_SIG) += signing_key.x509
 X509_CERTIFICATES := $(sort $(foreach CERT,$(X509_CERTIFICATES-y), \
@@ -169,10 +171,11 @@ $(shell rm $(obj)/.x509.list)
 endif
 endif
 
-kernel/modsign_certificate.o: $(obj)/x509_certificate_list
+kernel/system_certificates.o: $(obj)/x509_certificate_list
 
 quiet_cmd_x509certs  = CERTS   $@
-      cmd_x509certs  = cat $(X509_CERTIFICATES) /dev/null >$@
+      cmd_x509certs  = cat $(X509_CERTIFICATES) /dev/null >$@ $(foreach X509,$(X509_CERTIFICATES),; echo "  - Including cert $(X509)")
+
 targets += $(obj)/x509_certificate_list
 $(obj)/x509_certificate_list: $(X509_CERTIFICATES) $(obj)/.x509.list
 	$(call if_changed,x509certs)
@@ -182,7 +185,9 @@ $(obj)/.x509.list:
 	@echo $(X509_CERTIFICATES) >$@
 
 clean-files := x509_certificate_list .x509.list
+endif
 
+ifeq ($(CONFIG_MODULE_SIG),y)
 ###############################################################################
 #
 # If module signing is requested, say by allyesconfig, but a key has not been

kernel/module-internal.h

@@ -9,6 +9,4 @@
  * 2 of the Licence, or (at your option) any later version.
  */
 
-extern struct key *modsign_keyring;
-
 extern int mod_verify_sig(const void *mod, unsigned long *_modlen);

kernel/module_signing.c

@@ -14,6 +14,7 @@
 #include <crypto/public_key.h>
 #include <crypto/hash.h>
 #include <keys/asymmetric-type.h>
+#include <keys/system_keyring.h>
 #include "module-internal.h"
 
 /*
@@ -157,7 +158,7 @@ static struct key *request_asymmetric_key(const char *signer, size_t signer_len,
 
 	pr_debug("Look up: \"%s\"\n", id);
 
-	key = keyring_search(make_key_ref(modsign_keyring, 1),
+	key = keyring_search(make_key_ref(system_trusted_keyring, 1),
 			     &key_type_asymmetric, id);
 	if (IS_ERR(key))
 		pr_warn("Request for unknown module key '%s' err %ld\n",

kernel/modsign_certificate.S → kernel/system_certificates.S

@@ -1,11 +1,12 @@
 #include <linux/export.h>
+#include <linux/init.h>
 
 #define GLOBAL(name)	\
 	.globl VMLINUX_SYMBOL(name);	\
 	VMLINUX_SYMBOL(name):
 
-	.section ".init.data","aw"
+	__INITRODATA
 
-GLOBAL(modsign_certificate_list)
+GLOBAL(system_certificate_list)
 	.incbin "kernel/x509_certificate_list"
-GLOBAL(modsign_certificate_list_end)
+GLOBAL(system_certificate_list_end)

kernel/system_keyring.c

@@ -0,0 +1,103 @@
+/* System trusted keyring for trusted public keys
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([email protected])
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/cred.h>
+#include <linux/err.h>
+#include <keys/asymmetric-type.h>
+#include <keys/system_keyring.h>
+#include "module-internal.h"
+
+struct key *system_trusted_keyring;
+EXPORT_SYMBOL_GPL(system_trusted_keyring);
+
+extern __initconst const u8 system_certificate_list[];
+extern __initconst const u8 system_certificate_list_end[];
+
+/*
+ * Load the compiled-in keys
+ */
+static __init int system_trusted_keyring_init(void)
+{
+	pr_notice("Initialise system trusted keyring\n");
+
+	system_trusted_keyring =
+		keyring_alloc(".system_keyring",
+			      KUIDT_INIT(0), KGIDT_INIT(0), current_cred(),
+			      ((KEY_POS_ALL & ~KEY_POS_SETATTR) |
+			       KEY_USR_VIEW | KEY_USR_READ),
+			      KEY_ALLOC_NOT_IN_QUOTA, NULL);
+	if (IS_ERR(system_trusted_keyring))
+		panic("Can't allocate system trusted keyring\n");
+
+	return 0;
+}
+
+/*
+ * Must be initialised before we try and load the keys into the keyring.
+ */
+device_initcall(system_trusted_keyring_init);
+
+/*
+ * Load the compiled-in list of X.509 certificates.
+ */
+static __init int load_system_certificate_list(void)
+{
+	key_ref_t key;
+	const u8 *p, *end;
+	size_t plen;
+
+	pr_notice("Loading compiled-in X.509 certificates\n");
+
+	end = system_certificate_list_end;
+	p = system_certificate_list;
+	while (p < end) {
+		/* Each cert begins with an ASN.1 SEQUENCE tag and must be more
+		 * than 256 bytes in size.
+		 */
+		if (end - p < 4)
+			goto dodgy_cert;
+		if (p[0] != 0x30 &&
+		    p[1] != 0x82)
+			goto dodgy_cert;
+		plen = (p[2] << 8) | p[3];
+		plen += 4;
+		if (plen > end - p)
+			goto dodgy_cert;
+
+		key = key_create_or_update(make_key_ref(system_trusted_keyring, 1),
+					   "asymmetric",
+					   NULL,
+					   p,
+					   plen,
+					   (KEY_POS_ALL & ~KEY_POS_SETATTR) |
+					   KEY_USR_VIEW,
+					   KEY_ALLOC_NOT_IN_QUOTA);
+		if (IS_ERR(key)) {
+			pr_err("Problem loading in-kernel X.509 certificate (%ld)\n",
+			       PTR_ERR(key));
+		} else {
+			pr_notice("Loaded X.509 cert '%s'\n",
+				  key_ref_to_ptr(key)->description);
+			key_ref_put(key);
+		}
+		p += plen;
+	}
+
+	return 0;
+
+dodgy_cert:
+	pr_err("Problem parsing in-kernel X.509 certificate list\n");
+	return 0;
+}
+late_initcall(load_system_certificate_list);