[PATCH 20/25] MODSIGN: Provide module signing public keys to the kernel

[David Howells <dhowells@redhat.com>]

Include a PGP keyring containing the public keys required to perform module
verification in the kernel image during build and create a special keyring
during boot which is then populated with keys of crypto type holding the public
keys found in the PGP keyring.

These can be seen by root:

[root@andromeda ~]# cat /proc/keys
07ad4ee0 I-----     1 perm 3f010000     0     0 crypto    modsign.0: RSA 87b9b3bd []
15c7f8c3 I-----     1 perm 1f030000     0     0 keyring   .module_sign: 1/4
...

It is probably worth permitting root to invalidate these keys, resulting in
their removal and preventing further modules from being loaded with that key.

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

 kernel/Makefile         |    3 ++
 kernel/modsign-pubkey.c |   74 +++++++++++++++++++++++++++++++++++++++++++++++
 kernel/module-verify.h  |   14 +++++++++
 3 files changed, 91 insertions(+)
 create mode 100644 kernel/modsign-pubkey.c
 create mode 100644 kernel/module-verify.h


diff --git a/kernel/Makefile b/kernel/Makefile
index c0cc67a..84f6c04 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -55,6 +55,7 @@ obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock.o
 obj-$(CONFIG_PROVE_LOCKING) += spinlock.o
 obj-$(CONFIG_UID16) += uid16.o
 obj-$(CONFIG_MODULES) += module.o
+obj-$(CONFIG_MODULE_SIG) += modsign-pubkey.o
 obj-$(CONFIG_KALLSYMS) += kallsyms.o
 obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
 obj-$(CONFIG_KEXEC) += kexec.o
@@ -131,3 +132,5 @@ quiet_cmd_timeconst  = TIMEC   $@
 targets += timeconst.h
 $(obj)/timeconst.h: $(src)/timeconst.pl FORCE
 	$(call if_changed,timeconst)
+
+kernel/modsign-pubkey.o: modsign.pub
diff --git a/kernel/modsign-pubkey.c b/kernel/modsign-pubkey.c
new file mode 100644
index 0000000..ce14c9a
--- /dev/null
+++ b/kernel/modsign-pubkey.c
@@ -0,0 +1,74 @@
+/* Public keys for module signature verification
+ *
+ * Copyright (C) 2011 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/kernel.h>
+#include <linux/sched.h>
+#include <linux/cred.h>
+#include <keys/crypto-type.h>
+#include "module-verify.h"
+
+struct key *modsign_keyring;
+
+extern __initdata const u8 modsign_public_keys[];
+extern __initdata const u8 modsign_public_keys_end[];
+asm(".section .init.data,\"aw\"\n"
+    "modsign_public_keys:\n"
+    ".incbin \"modsign.pub\"\n"
+    "modsign_public_keys_end:"
+    );
+
+/*
+ * We need to make sure ccache doesn't cache the .o file as it doesn't notice
+ * if modsign.pub changes.
+ */
+static __initdata const char annoy_ccache[] = __TIME__ "foo";
+
+/*
+ * Load the compiled-in keys
+ */
+static __init int module_verify_init(void)
+{
+	pr_notice("Initialise module verification\n");
+
+	modsign_keyring = key_alloc(&key_type_keyring, ".module_sign",
+				    0, 0, current_cred(),
+				    (KEY_POS_ALL & ~KEY_POS_SETATTR) |
+				    KEY_USR_VIEW | KEY_USR_READ,
+				    KEY_ALLOC_NOT_IN_QUOTA);
+	if (IS_ERR(modsign_keyring))
+		panic("Can't allocate module signing keyring\n");
+
+	if (key_instantiate_and_link(modsign_keyring, NULL, 0, NULL, NULL) < 0)
+		panic("Can't instantiate module signing keyring\n");
+
+	return 0;
+}
+
+/*
+ * Must be initialised before we try and load the keys into the keyring.
+ */
+device_initcall(module_verify_init);
+
+/*
+ * Load the compiled-in keys
+ */
+static __init int modsign_pubkey_init(void)
+{
+	pr_notice("Load module verification keys\n");
+
+	if (preload_pgp_keys(modsign_public_keys,
+			     modsign_public_keys_end - modsign_public_keys,
+			     modsign_keyring) < 0)
+		panic("Can't load module signing keys\n");
+
+	return 0;
+}
+late_initcall(modsign_pubkey_init);
diff --git a/kernel/module-verify.h b/kernel/module-verify.h
new file mode 100644
index 0000000..2f6cc16
--- /dev/null
+++ b/kernel/module-verify.h
@@ -0,0 +1,14 @@
+/* Module verification definitions
+ *
+ * Copyright (C) 2004, 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.
+ */
+
+#ifdef CONFIG_MODULE_SIG
+extern struct key *modsign_keyring;
+#endif