Commit 631cc66e authored by David Howells's avatar David Howells Committed by Rusty Russell
Browse files

MODSIGN: Provide module signing public keys to the kernel 



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: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent d441108c

kernel/Makefile

+9 −2
Original line number Diff line number Diff line
@@ -55,7 +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) += module_signing.o

obj-$(CONFIG_MODULE_SIG) += module_signing.o modsign_pubkey.o

obj-$(CONFIG_KALLSYMS) += kallsyms.o

obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o

obj-$(CONFIG_KEXEC) += kexec.o
@@ -134,6 +134,13 @@ $(obj)/timeconst.h: $(src)/timeconst.pl FORCE 
	$(call if_changed,timeconst)



ifeq ($(CONFIG_MODULE_SIG),y)

#

# Pull the signing certificate and any extra certificates into the kernel

#

extra_certificates:

	touch $@



kernel/modsign_pubkey.o: signing_key.x509 extra_certificates



###############################################################################

#
@@ -180,4 +187,4 @@ x509.genkey: 
	@echo >>x509.genkey "subjectKeyIdentifier=hash"

	@echo >>x509.genkey "authorityKeyIdentifier=keyid"

endif

CLEAN_FILES += signing_key.priv signing_key.x509 x509.genkey
 
CLEAN_FILES += signing_key.priv signing_key.x509 x509.genkey extra_certificates

kernel/modsign_pubkey.c

0 → 100644
+113 −0
Original line number Diff line number Diff line 
/* Public keys for module signature verification

 *

 * 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/kernel.h>

#include <linux/sched.h>

#include <linux/cred.h>

#include <linux/err.h>

#include <keys/asymmetric-type.h>

#include "module-internal.h"



struct key *modsign_keyring;



extern __initdata const u8 modsign_certificate_list[];

extern __initdata const u8 modsign_certificate_list_end[];

asm(".section .init.data,\"aw\"\n"

    "modsign_certificate_list:\n"

    ".incbin \"signing_key.x509\"\n"

    ".incbin \"extra_certificates\"\n"

    "modsign_certificate_list_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",

				    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);

	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 load_module_signing_keys(void)

{

	key_ref_t key;

	const u8 *p, *end;

	size_t plen;



	pr_notice("Loading module verification certificates\n");



	end = modsign_certificate_list_end;

	p = modsign_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(modsign_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("MODSIGN: Problem loading in-kernel X.509 certificate (%ld)\n",

			       PTR_ERR(key));

		else

			pr_notice("MODSIGN: Loaded cert '%s'\n",

				  key_ref_to_ptr(key)->description);

		p += plen;

	}



	return 0;



dodgy_cert:

	pr_err("MODSIGN: Problem parsing in-kernel X.509 certificate list\n");

	return 0;

}

late_initcall(load_module_signing_keys);

kernel/module-internal.h

+2 −0
Original line number Diff line number Diff line
@@ -9,5 +9,7 @@ 
 * 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,

			  const void *sig, unsigned long siglen);

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