From 6a3f34b43ad377eb7473425f7525e403de384be5 Mon Sep 17 00:00:00 2001
From: "Lee, Chun-Yi" <jlee@suse.com>
Date: Wed, 29 Nov 2017 18:44:57 +0800
Subject: [PATCH 4/4] MODSIGN: checking the blacklisted hash before loading a
 kernel module
Patch-mainline: No, submitted https://patchwork.kernel.org/patch/10082315/
References: fate#316531, bnc#854875

This patch adds the logic for checking the kernel module's hash
base on blacklist. The hash must be generated by sha256 and enrolled
to dbx/mokx.

For example:
	sha256sum sample.ko
	mokutil --mokx --import-hash $HASH_RESULT

Whether the signature on ko file is stripped or not, the hash can be
compared by kernel.

Signed-off-by: Lee, Chun-Yi <jlee@suse.com>
---
 kernel/module_signing.c |   61 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 59 insertions(+), 2 deletions(-)

--- a/kernel/module_signing.c
+++ b/kernel/module_signing.c
@@ -15,6 +15,8 @@
 #include <linux/verification.h>
 #include <linux/module.h>
 #include <crypto/public_key.h>
+#include <crypto/hash.h>
+#include <keys/system_keyring.h>
 #include "module-internal.h"
 
 enum pkey_id_type {
@@ -43,19 +45,67 @@ struct module_signature {
 	__be32	sig_len;	/* Length of signature data */
 };
 
+static int mod_is_hash_blacklisted(const void *mod, size_t verifylen)
+{
+	struct crypto_shash *tfm;
+	struct shash_desc *desc;
+	size_t digest_size, desc_size;
+	u8 *digest;
+	int ret = 0;
+
+	tfm = crypto_alloc_shash("sha256", 0, 0);
+	if (IS_ERR(tfm))
+		goto error_return;
+
+	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, verifylen, digest);
+	if (ret < 0)
+		goto error_shash;
+
+	pr_debug("%ld digest: %*phN\n", verifylen, (int) digest_size, digest);
+
+	ret = is_hash_blacklisted(digest, digest_size, "bin");
+	if (ret == -EKEYREJECTED)
+		pr_err("Module hash %*phN is blacklisted\n",
+		       (int) digest_size, digest);
+
+error_shash:
+	kfree(digest);
+error_digest:
+	crypto_free_shash(tfm);
+error_return:
+	return ret;
+}
+
 /*
  * Verify the signature on a module.
  */
 int mod_verify_sig(const void *mod, struct load_info *info)
 {
 	struct module_signature ms;
-	size_t modlen = info->len, sig_len;
+	size_t modlen = info->len, sig_len, wholelen;
+	int ret;
 
 	pr_devel("==>%s(,%zu)\n", __func__, modlen);
 
 	if (modlen <= sizeof(ms))
 		return -EBADMSG;
 
+	wholelen = modlen + sizeof(MODULE_SIG_STRING) - 1;
 	memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
 	modlen -= sizeof(ms);
 
@@ -83,7 +133,14 @@ int mod_verify_sig(const void *mod, stru
 		return -EBADMSG;
 	}
 
-	return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
+	ret = verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
 				      (void *)1UL, VERIFYING_MODULE_SIGNATURE,
 				      NULL, NULL);
+	pr_devel("verify_pkcs7_signature() = %d\n", ret);
+
+	/* checking hash of module is in blacklist */
+	if (!ret)
+		ret = mod_is_hash_blacklisted(mod, wholelen);
+
+	return ret;
 }