MODSIGN: Export module signature definitions

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.

s390 duplicated the definition of struct module_signature so now they can
use the new <linux/module_signature.h> header instead.

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Acked-by: Jessica Yu <jeyu@kernel.org>
Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

10 files changed, 108 insertions, 77 deletions

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index a4ad2733eedf..e0ae0d51f985 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -538,7 +538,7 @@ config ARCH_HAS_KEXEC_PURGATORY
 
 config KEXEC_VERIFY_SIG
         bool "Verify kernel signature during kexec_file_load() syscall"
-        depends on KEXEC_FILE && SYSTEM_DATA_VERIFICATION
+        depends on KEXEC_FILE && MODULE_SIG_FORMAT
         help
           This option makes kernel signature verification mandatory for
           the kexec_file_load() syscall.
diff --git a/arch/s390/kernel/machine_kexec_file.c b/arch/s390/kernel/machine_kexec_file.c
index fbdd3ea73667..1ac9fbc6e01e 100644
--- a/arch/s390/kernel/machine_kexec_file.c
+++ b/arch/s390/kernel/machine_kexec_file.c
@@ -10,7 +10,7 @@
 #include <linux/elf.h>
 #include <linux/errno.h>
 #include <linux/kexec.h>
-#include <linux/module.h>
+#include <linux/module_signature.h>
 #include <linux/verification.h>
 #include <asm/boot_data.h>
 #include <asm/ipl.h>
@@ -23,28 +23,6 @@ const struct kexec_file_ops * const kexec_file_loaders[] = {
 };
 
 #ifdef CONFIG_KEXEC_VERIFY_SIG
-/*
- * 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 */
-};
-
-#define PKEY_ID_PKCS7 2
-
 int s390_verify_sig(const char *kernel, unsigned long kernel_len)
 {
         const unsigned long marker_len = sizeof(MODULE_SIG_STRING) - 1;
diff --git a/include/linux/module.h b/include/linux/module.h
index 1455812dd325..f6fc1dae74f4 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -26,9 +26,6 @@
 #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 bd7d650d4a99..2dca877c9ed7 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1930,6 +1930,10 @@ 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
@@ -2007,7 +2011,7 @@ 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 a8d923b5481b..179b44ab8b46 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 5933395af9a0..5ac22efc3685 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -7,6 +7,7 @@
 #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 b10fb1986ca9..9d9fc678c91d 100644
--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -7,37 +7,13 @@
 
 #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.
  */
@@ -45,6 +21,7 @@ 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);
 
@@ -52,32 +29,15 @@ 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 16bcb8087899..532f7e0915c3 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