[PATCH 1/2] MODSIGN: check hash of kernel module in blacklist

[Lee, Chun-Yi]

This patch introduces a blacklist list of kernel module's hash. It check
the blacklist before checking kernel module signature.
It didn't limit what hash algorithm used but the module of hash algorithm
need build-in or put in initrd for verify kernel module in initrd.

Signed-off-by: Lee, Chun-Yi <jlee at suse.com>
---
 kernel/module-internal.h |   14 ++++++++
 kernel/module.c          |    9 +++++-
 kernel/module_signing.c  |   79 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 101 insertions(+), 1 deletions(-)

diff --git a/kernel/module-internal.h b/kernel/module-internal.h
index 915e123..f1b6477 100644
--- a/kernel/module-internal.h
+++ b/kernel/module-internal.h
@@ -9,4 +9,18 @@
  * 2 of the Licence, or (at your option) any later version.
  */
 
+/*
+ * Module hash.
+ */
+struct module_hash {
+	struct list_head list;  /* list of all hashs */
+	u8 hash;                /* Hash algorithm [enum pkey_hash_algo] */
+	char *hash_name;        /* nams string of hash */
+	size_t size;            /* size of hash */
+	u8 hash_data[];         /* Hash data */
+};
+
+extern struct list_head module_hash_blacklist;
+
+extern int mod_verify_hash(const void *mod, unsigned long modlen);
 extern int mod_verify_sig(const void *mod, unsigned long *_modlen);
diff --git a/kernel/module.c b/kernel/module.c
index 3305511..dd06d8a 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2562,10 +2562,16 @@ static inline void kmemleak_load_module(const struct module *mod,
 #ifdef CONFIG_MODULE_SIG
 static int module_sig_check(struct load_info *info)
 {
-	int err = -ENOKEY;
+	int err;
 	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
 	const void *mod = info->hdr;
 
+	/* check hash of module in blacklist */
+	err = mod_verify_hash(mod, info->len);
+	if (err)
+		goto match_blacklist_hash;
+
+	err = -ENOKEY;
 	if (info->len > markerlen &&
 	    memcmp(mod + info->len - markerlen, MODULE_SIG_STRING, markerlen) == 0) {
 		/* We truncate the module to discard the signature */
@@ -2578,6 +2584,7 @@ static int module_sig_check(struct load_info *info)
 		return 0;
 	}
 
+match_blacklist_hash:
 	/* Not having a signature is only an error if we're strict. */
 	if (err < 0 && fips_enabled)
 		panic("Module verification failed with error %d in FIPS mode\n",
diff --git a/kernel/module_signing.c b/kernel/module_signing.c
index 0a29b40..cd7f441 100644
--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -11,12 +11,15 @@
 
 #include <linux/kernel.h>
 #include <linux/err.h>
+#include <linux/module.h>
 #include <crypto/public_key.h>
 #include <crypto/hash.h>
 #include <keys/asymmetric-type.h>
 #include <keys/system_keyring.h>
 #include "module-internal.h"
 
+LIST_HEAD(module_hash_blacklist);
+
 /*
  * Module signature information block.
  *
@@ -193,6 +196,82 @@ static struct key *request_asymmetric_key(const char *signer, size_t signer_len,
 	return key_ref_to_ptr(key);
 }
 
+int mod_verify_hash(const void *mod, unsigned long modlen)
+{
+	struct module_signature ms;
+	struct module_hash *module_hash;
+	struct crypto_shash *tfm;
+	struct shash_desc *desc;
+	size_t digest_size, desc_size;
+	size_t sig_len;
+	u8 *digest;
+	int ret = 0;
+
+	const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
+
+	/* truncate the module to discard the signature when it signed */
+	if (modlen > markerlen &&
+	    memcmp(mod + modlen - markerlen, MODULE_SIG_STRING, markerlen) == 0) {
+		modlen -= markerlen;
+		if (modlen <= sizeof(ms))
+			return -EBADMSG;
+		memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
+		modlen -= sizeof(ms);
+		sig_len = be32_to_cpu(ms.sig_len);
+		if (sig_len >= modlen)
+			return -EBADMSG;
+		modlen -= sig_len;
+		if ((size_t)ms.signer_len + ms.key_id_len >= modlen)
+			return -EBADMSG;
+		modlen -= (size_t)ms.signer_len + ms.key_id_len;
+	}
+
+	list_for_each_entry(module_hash, &module_hash_blacklist, list) {
+		tfm = crypto_alloc_shash(module_hash->hash_name, 0, 0);
+		if (IS_ERR(tfm)) {
+			printk_once(KERN_WARNING "The %s hash algorithm did "
+				"not load for check blacklisted module hash: "
+				"%*phN\n", module_hash->hash_name,
+				(int) module_hash->size,
+				module_hash->hash_data);
+			continue;
+		}
+
+		desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+		digest_size = crypto_shash_digestsize(tfm);
+		digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
+		if (!digest) {
+			pr_err("digest memory buffer allocate fail\n");
+			ret = -ENOMEM;
+			goto error_digest;
+		}
+		desc = (void *)digest + digest_size;
+		desc->tfm = tfm;
+		desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+		ret = crypto_shash_init(desc);
+		if (ret < 0)
+			goto error_shash;
+
+		ret = crypto_shash_finup(desc, mod, modlen, digest);
+		if (ret < 0)
+			goto error_shash;
+
+		if (!memcmp(digest, module_hash->hash_data, digest_size)) {
+			ret = -EKEYREJECTED;
+			pr_info("Module Hash is in MOKx blacklisted: %*phN\n",
+				(int) module_hash->size, module_hash->hash_data);
+		}
+error_shash:
+		kfree(digest);
+error_digest:
+		crypto_free_shash(tfm);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+
 /*
  * Verify the signature on a module.
  */
-- 
1.6.4.2