[PATCH v12 01/11] MODSIGN: Export module signature definitions

Thiago Jung Bauermann
2019-06-28T02:20:40Z

IMA will use the module_signature format for append signatures, so export
the relevant definitions and factor out the code which verifies that the
appended signature trailer is valid.

Also, create a CONFIG_MODULE_SIG_FORMAT option so that IMA can select it
and be able to use mod_check_sig() without having to depend on either
CONFIG_MODULE_SIG or CONFIG_MODULES.

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Cc: Jessica Yu <jeyu@kernel.org>
---
include/linux/module.h | 3 --
include/linux/module_signature.h | 44 +++++++++++++++++++++++++
init/Kconfig | 6 +++-
kernel/Makefile | 1 +
kernel/module.c | 1 +
kernel/module_signature.c | 46 ++++++++++++++++++++++++++
kernel/module_signing.c | 56 +++++---------------------------
scripts/Makefile | 2 +-
8 files changed, 106 insertions(+), 53 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 188998d3dca9..aa56f531cf1e 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -25,9 +25,6 @@
#include <linux/percpu.h>
#include <asm/module.h>

-/* In stripped ARM and x86-64 modules, ~ is surprisingly rare. */
-#define MODULE_SIG_STRING "~Module signature appended~\n"
-
/* Not Yet Implemented */
#define MODULE_SUPPORTED_DEVICE(name)

diff --git a/include/linux/module_signature.h b/include/linux/module_signature.h
new file mode 100644
index 000000000000..523617fc5b6a
--- /dev/null
+++ b/include/linux/module_signature.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Module signature handling.
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#ifndef _LINUX_MODULE_SIGNATURE_H
+#define _LINUX_MODULE_SIGNATURE_H
+
+/* In stripped ARM and x86-64 modules, ~ is surprisingly rare. */
+#define MODULE_SIG_STRING "~Module signature appended~\n"
+
+enum pkey_id_type {
+ PKEY_ID_PGP, /* OpenPGP generated key ID */
+ PKEY_ID_X509, /* X.509 arbitrary subjectKeyIdentifier */
+ PKEY_ID_PKCS7, /* Signature in PKCS#7 message */
+};
+
+/*
+ * Module signature information block.
+ *
+ * The constituents of the signature section are, in order:
+ *
+ * - Signer's name
+ * - Key identifier
+ * - Signature data
+ * - Information block
+ */
+struct module_signature {
+ u8 algo; /* Public-key crypto algorithm [0] */
+ u8 hash; /* Digest algorithm [0] */
+ u8 id_type; /* Key identifier type [PKEY_ID_PKCS7] */
+ u8 signer_len; /* Length of signer's name [0] */
+ u8 key_id_len; /* Length of key identifier [0] */
+ u8 __pad[3];
+ __be32 sig_len; /* Length of signature data */
+};
+
+int mod_check_sig(const struct module_signature *ms, size_t file_len,
+ const char *name);
+
+#endif /* _LINUX_MODULE_SIGNATURE_H */
diff --git a/init/Kconfig b/init/Kconfig
index 8b9ffe236e4f..c2286a3c74c5 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1852,6 +1852,10 @@ config BASE_SMALL
default 0 if BASE_FULL
default 1 if !BASE_FULL

+config MODULE_SIG_FORMAT
+ def_bool n
+ select SYSTEM_DATA_VERIFICATION
+
menuconfig MODULES
bool "Enable loadable module support"
option modules
@@ -1929,7 +1933,7 @@ config MODULE_SRCVERSION_ALL
config MODULE_SIG
bool "Module signature verification"
depends on MODULES
- select SYSTEM_DATA_VERIFICATION
+ select MODULE_SIG_FORMAT
help
Check modules for valid signatures upon load: the signature
is simply appended to the module. For more information see
diff --git a/kernel/Makefile b/kernel/Makefile
index 33824f0385b3..f29ae2997a43 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -58,6 +58,7 @@ endif
obj-$(CONFIG_UID16) += uid16.o
obj-$(CONFIG_MODULES) += module.o
obj-$(CONFIG_MODULE_SIG) += module_signing.o
+obj-$(CONFIG_MODULE_SIG_FORMAT) += module_signature.o
obj-$(CONFIG_KALLSYMS) += kallsyms.o
obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
obj-$(CONFIG_CRASH_CORE) += crash_core.o
diff --git a/kernel/module.c b/kernel/module.c
index 6e6712b3aaf5..2712f4d217f5 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -19,6 +19,7 @@
#include <linux/export.h>
#include <linux/extable.h>
#include <linux/moduleloader.h>
+#include <linux/module_signature.h>
#include <linux/trace_events.h>
#include <linux/init.h>
#include <linux/kallsyms.h>
diff --git a/kernel/module_signature.c b/kernel/module_signature.c
new file mode 100644
index 000000000000..4224a1086b7d
--- /dev/null
+++ b/kernel/module_signature.c
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Module signature checker
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/errno.h>
+#include <linux/printk.h>
+#include <linux/module_signature.h>
+#include <asm/byteorder.h>
+
+/**
+ * mod_check_sig - check that the given signature is sane
+ *
+ * @ms: Signature to check.
+ * @file_len: Size of the file to which @ms is appended.
+ * @name: What is being checked. Used for error messages.
+ */
+int mod_check_sig(const struct module_signature *ms, size_t file_len,
+ const char *name)
+{
+ if (be32_to_cpu(ms->sig_len) >= file_len - sizeof(*ms))
+ return -EBADMSG;
+
+ if (ms->id_type != PKEY_ID_PKCS7) {
+ pr_err("%s: Module is not signed with expected PKCS#7 message\n",
+ name);
+ return -ENOPKG;
+ }
+
+ if (ms->algo != 0 ||
+ ms->hash != 0 ||
+ ms->signer_len != 0 ||
+ ms->key_id_len != 0 ||
+ ms->__pad[0] != 0 ||
+ ms->__pad[1] != 0 ||
+ ms->__pad[2] != 0) {
+ pr_err("%s: PKCS#7 signature info has unexpected non-zero params\n",
+ name);
+ return -EBADMSG;
+ }
+
+ return 0;
+}
diff --git a/kernel/module_signing.c b/kernel/module_signing.c
index 6b9a926fd86b..cdd04a6b8074 100644
--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -11,37 +11,13 @@

#include <linux/kernel.h>
#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/module_signature.h>
#include <linux/string.h>
#include <linux/verification.h>
#include <crypto/public_key.h>
#include "module-internal.h"

-enum pkey_id_type {
- PKEY_ID_PGP, /* OpenPGP generated key ID */
- PKEY_ID_X509, /* X.509 arbitrary subjectKeyIdentifier */
- PKEY_ID_PKCS7, /* Signature in PKCS#7 message */
-};
-
-/*
- * Module signature information block.
- *
- * The constituents of the signature section are, in order:
- *
- * - Signer's name
- * - Key identifier
- * - Signature data
- * - Information block
- */
-struct module_signature {
- u8 algo; /* Public-key crypto algorithm [0] */
- u8 hash; /* Digest algorithm [0] */
- u8 id_type; /* Key identifier type [PKEY_ID_PKCS7] */
- u8 signer_len; /* Length of signer's name [0] */
- u8 key_id_len; /* Length of key identifier [0] */
- u8 __pad[3];
- __be32 sig_len; /* Length of signature data */
-};
-
/*
* Verify the signature on a module.
*/
@@ -49,6 +25,7 @@ int mod_verify_sig(const void *mod, struct load_info *info)
{
struct module_signature ms;
size_t sig_len, modlen = info->len;
+ int ret;

pr_devel("==>%s(,%zu)\n", __func__, modlen);

@@ -56,32 +33,15 @@ int mod_verify_sig(const void *mod, struct load_info *info)
return -EBADMSG;

memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
- modlen -= sizeof(ms);
+
+ ret = mod_check_sig(&ms, modlen, info->name);
+ if (ret)
+ return ret;

sig_len = be32_to_cpu(ms.sig_len);
- if (sig_len >= modlen)
- return -EBADMSG;
- modlen -= sig_len;
+ modlen -= sig_len + sizeof(ms);
info->len = modlen;

- if (ms.id_type != PKEY_ID_PKCS7) {
- pr_err("%s: Module is not signed with expected PKCS#7 message\n",
- info->name);
- return -ENOPKG;
- }
-
- if (ms.algo != 0 ||
- ms.hash != 0 ||
- ms.signer_len != 0 ||
- ms.key_id_len != 0 ||
- ms.__pad[0] != 0 ||
- ms.__pad[1] != 0 ||
- ms.__pad[2] != 0) {
- pr_err("%s: PKCS#7 signature info has unexpected non-zero params\n",
- info->name);
- return -EBADMSG;
- }
-
return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
VERIFY_USE_SECONDARY_KEYRING,
VERIFYING_MODULE_SIGNATURE,
diff --git a/scripts/Makefile b/scripts/Makefile
index 9d442ee050bd..52098b080ab7 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -17,7 +17,7 @@ hostprogs-$(CONFIG_VT) += conmakehash
hostprogs-$(BUILD_C_RECORDMCOUNT) += recordmcount
hostprogs-$(CONFIG_BUILDTIME_EXTABLE_SORT) += sortextable
hostprogs-$(CONFIG_ASN1) += asn1_compiler
-hostprogs-$(CONFIG_MODULE_SIG) += sign-file
+hostprogs-$(CONFIG_MODULE_SIG_FORMAT) += sign-file
hostprogs-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += extract-cert
hostprogs-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE) += insert-sys-cert