[PATCH v9 01/14] MODSIGN: Export module signature definitions

[Thiago Jung Bauermann]

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
CONFIG_MODULE_SIG.

Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Cc: Jessica Yu <jeyu@xxxxxxxxxx>
---
 include/linux/module.h           |  3 --
 include/linux/module_signature.h | 47 ++++++++++++++++++
 init/Kconfig                     |  6 ++-
 kernel/Makefile                  |  2 +-
 kernel/module.c                  |  1 +
 kernel/module_signing.c          | 82 ++++++++++++++------------------
 6 files changed, 91 insertions(+), 50 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index fce6b4335e36..e49bbc5c66ef 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..a3a629fc8c13
--- /dev/null
+++ b/include/linux/module_signature.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Module signature handling.
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@xxxxxxxxxx)
+ */
+
+#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 */
+};
+
+struct load_info;
+
+int mod_check_sig(const struct module_signature *ms, size_t file_len,
+		  const char *name);
+int mod_verify_sig(const void *mod, struct load_info *info);
+
+#endif /* _LINUX_MODULE_SIGNATURE_H */
diff --git a/init/Kconfig b/init/Kconfig
index a4112e95724a..cd31593525ee 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1864,7 +1864,7 @@ 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
@@ -1879,6 +1879,10 @@ config MODULE_SIG
 	  debuginfo strip done by some packagers (such as rpmbuild) and
 	  inclusion into an initramfs that wants the module size reduced.
 
+config MODULE_SIG_FORMAT
+	def_bool n
+	select SYSTEM_DATA_VERIFICATION
+
 config MODULE_SIG_FORCE
 	bool "Require modules to be validly signed"
 	depends on MODULE_SIG
diff --git a/kernel/Makefile b/kernel/Makefile
index 7343b3a9bff0..e56842571348 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -59,7 +59,7 @@ obj-y += up.o
 endif
 obj-$(CONFIG_UID16) += uid16.o
 obj-$(CONFIG_MODULES) += module.o
-obj-$(CONFIG_MODULE_SIG) += module_signing.o
+obj-$(CONFIG_MODULE_SIG_FORMAT) += module_signing.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 49a405891587..205c9eefd08d 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_signing.c b/kernel/module_signing.c
index f2075ce8e4b3..5624e59981b4 100644
--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -11,36 +11,44 @@
 
 #include <linux/kernel.h>
 #include <linux/errno.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.
+/**
+ * mod_check_sig - check that the given signature is sane
  *
- * The constituents of the signature section are, in order:
- *
- *	- Signer's name
- *	- Key identifier
- *	- Signature data
- *	- Information block
+ * @ms:		Signature to check.
+ * @file_len:	Size of the file to which @ms is appended.
  */
-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)
+{
+	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;
+}
 
 /*
  * Verify the signature on a module.
@@ -49,6 +57,7 @@ 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 +65,15 @@ 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,
 				      NULL, VERIFYING_MODULE_SIGNATURE,
 				      NULL, NULL);