Move certificate handling to its own directory

Move certificate handling out of the kernel/ directory and into a certs/
directory to get all the weird stuff in one place and move the generated
signing keys into this directory.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: David Woodhouse <David.Woodhouse@intel.com>

4 files changed, 369 insertions, 0 deletions

diff --git a/certs/Kconfig b/certs/Kconfig
new file mode 100644
index 000000000000..b030b9c7ed34
--- /dev/null
+++ b/certs/Kconfig
@@ -0,0 +1,42 @@
+menu "Certificates for signature checking"
+
+config MODULE_SIG_KEY
+        string "File name or PKCS#11 URI of module signing key"
+        default "certs/signing_key.pem"
+        depends on MODULE_SIG
+        help
+         Provide the file name of a private key/certificate in PEM format,
+         or a PKCS#11 URI according to RFC7512. The file should contain, or
+         the URI should identify, both the certificate and its corresponding
+         private key.
+
+         If this option is unchanged from its default "certs/signing_key.pem",
+         then the kernel will automatically generate the private key and
+         certificate as described in Documentation/module-signing.txt
+
+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.
+
+config SYSTEM_TRUSTED_KEYS
+        string "Additional X.509 keys for default system keyring"
+        depends on SYSTEM_TRUSTED_KEYRING
+        help
+          If set, this option should be the filename of a PEM-formatted file
+          containing trusted X.509 certificates to be included in the default
+          system keyring. Any certificate used for module signing is implicitly
+          also trusted.
+
+          NOTE: If you previously provided keys for the system keyring in the
+          form of DER-encoded *.x509 files in the top-level build directory,
+          those are no longer used. You will need to set this option instead.
+
+endmenu
diff --git a/certs/Makefile b/certs/Makefile
new file mode 100644
index 000000000000..5d33486d3b20
--- /dev/null
+++ b/certs/Makefile
@@ -0,0 +1,147 @@
+#
+# Makefile for the linux kernel signature checking certificates.
+#
+
+obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o
+
+###############################################################################
+#
+# When a Kconfig string contains a filename, it is suitable for
+# passing to shell commands. It is surrounded by double-quotes, and
+# any double-quotes or backslashes within it are escaped by
+# backslashes.
+#
+# This is no use for dependencies or $(wildcard). We need to strip the
+# surrounding quotes and the escaping from quotes and backslashes, and
+# we *do* need to escape any spaces in the string. So, for example:
+#
+# Usage: $(eval $(call config_filename,FOO))
+#
+# Defines FOO_FILENAME based on the contents of the CONFIG_FOO option,
+# transformed as described above to be suitable for use within the
+# makefile.
+#
+# Also, if the filename is a relative filename and exists in the source
+# tree but not the build tree, define FOO_SRCPREFIX as $(srctree)/ to
+# be prefixed to *both* command invocation and dependencies.
+#
+# Note: We also print the filenames in the quiet_cmd_foo text, and
+# perhaps ought to have a version specially escaped for that purpose.
+# But it's only cosmetic, and $(patsubst "%",%,$(CONFIG_FOO)) is good
+# enough.  It'll strip the quotes in the common case where there's no
+# space and it's a simple filename, and it'll retain the quotes when
+# there's a space. There are some esoteric cases in which it'll print
+# the wrong thing, but we don't really care. The actual dependencies
+# and commands *do* get it right, with various combinations of single
+# and double quotes, backslashes and spaces in the filenames.
+#
+###############################################################################
+#
+quote := $(firstword " ")
+space :=
+space +=
+space_escape := %%%SPACE%%%
+#
+define config_filename
+ifneq ($$(CONFIG_$(1)),"")
+$(1)_FILENAME := $$(subst \\,\,$$(subst \$$(quote),$$(quote),$$(subst $$(space_escape),\$$(space),$$(patsubst "%",%,$$(subst $$(space),$$(space_escape),$$(CONFIG_$(1)))))))
+ifneq ($$(patsubst /%,%,$$(firstword $$($(1)_FILENAME))),$$(firstword $$($(1)_FILENAME)))
+else
+ifeq ($$(wildcard $$($(1)_FILENAME)),)
+ifneq ($$(wildcard $$(srctree)/$$($(1)_FILENAME)),)
+$(1)_SRCPREFIX := $(srctree)/
+endif
+endif
+endif
+endif
+endef
+#
+###############################################################################
+
+ifeq ($(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: $(obj)/signing_key.x509
+
+$(obj)/signing_key.x509: scripts/extract-cert include/config/module/sig/key.h $(X509_DEP)
+        $(call cmd,extract_certs,$(MODULE_SIG_KEY_SRCPREFIX)$(CONFIG_MODULE_SIG_KEY))
+endif
diff --git a/certs/system_certificates.S b/certs/system_certificates.S
new file mode 100644
index 000000000000..9216e8c81764
--- /dev/null
+++ b/certs/system_certificates.S
@@ -0,0 +1,23 @@
+#include <linux/export.h>
+#include <linux/init.h>
+
+        __INITRODATA
+
+        .align 8
+        .globl VMLINUX_SYMBOL(system_certificate_list)
+VMLINUX_SYMBOL(system_certificate_list):
+__cert_list_start:
+#ifdef CONFIG_MODULE_SIG
+        .incbin "certs/signing_key.x509"
+#endif
+        .incbin "certs/x509_certificate_list"
+__cert_list_end:
+
+        .align 8
+        .globl VMLINUX_SYMBOL(system_certificate_list_size)
+VMLINUX_SYMBOL(system_certificate_list_size):
+#ifdef CONFIG_64BIT
+        .quad __cert_list_end - __cert_list_start
+#else
+        .long __cert_list_end - __cert_list_start
+#endif
diff --git a/certs/system_keyring.c b/certs/system_keyring.c
new file mode 100644
index 000000000000..2570598b784d
--- /dev/null
+++ b/certs/system_keyring.c
@@ -0,0 +1,157 @@
+/* System trusted keyring for trusted public keys
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * 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 <crypto/pkcs7.h>
+
+struct key *system_trusted_keyring;
+EXPORT_SYMBOL_GPL(system_trusted_keyring);
+
+extern __initconst const u8 system_certificate_list[];
+extern __initconst const unsigned long system_certificate_list_size;
+
+/*
+ * 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_USR_SEARCH),
+                              KEY_ALLOC_NOT_IN_QUOTA, NULL);
+        if (IS_ERR(system_trusted_keyring))
+                panic("Can't allocate system trusted keyring\n");
+
+        set_bit(KEY_FLAG_TRUSTED_ONLY, &system_trusted_keyring->flags);
+        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");
+
+        p = system_certificate_list;
+        end = p + system_certificate_list_size;
+        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_USR_READ),
+                                           KEY_ALLOC_NOT_IN_QUOTA |
+                                           KEY_ALLOC_TRUSTED);
+                if (IS_ERR(key)) {
+                        pr_err("Problem loading in-kernel X.509 certificate (%ld)\n",
+                               PTR_ERR(key));
+                } else {
+                        set_bit(KEY_FLAG_BUILTIN, &key_ref_to_ptr(key)->flags);
+                        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);
+
+#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
+
+/**
+ * Verify a PKCS#7-based signature on system data.
+ * @data: The data to be verified.
+ * @len: Size of @data.
+ * @raw_pkcs7: The PKCS#7 message that is the signature.
+ * @pkcs7_len: The size of @raw_pkcs7.
+ * @usage: The use to which the key is being put.
+ */
+int system_verify_data(const void *data, unsigned long len,
+                       const void *raw_pkcs7, size_t pkcs7_len,
+                       enum key_being_used_for usage)
+{
+        struct pkcs7_message *pkcs7;
+        bool trusted;
+        int ret;
+
+        pkcs7 = pkcs7_parse_message(raw_pkcs7, pkcs7_len);
+        if (IS_ERR(pkcs7))
+                return PTR_ERR(pkcs7);
+
+        /* The data should be detached - so we need to supply it. */
+        if (pkcs7_supply_detached_data(pkcs7, data, len) < 0) {
+                pr_err("PKCS#7 signature with non-detached data\n");
+                ret = -EBADMSG;
+                goto error;
+        }
+
+        ret = pkcs7_verify(pkcs7, usage);
+        if (ret < 0)
+                goto error;
+
+        ret = pkcs7_validate_trust(pkcs7, system_trusted_keyring, &trusted);
+        if (ret < 0)
+                goto error;
+
+        if (!trusted) {
+                pr_err("PKCS#7 signature not signed with a trusted key\n");
+                ret = -ENOKEY;
+        }
+
+error:
+        pkcs7_free_message(pkcs7);
+        pr_devel("<==%s() = %d\n", __func__, ret);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(system_verify_data);
+
+#endif /* CONFIG_SYSTEM_DATA_VERIFICATION */