evm: digital signature verification support

This patch adds support for digital signature verification to EVM.
With this feature file metadata can be protected using digital
signature instead of an HMAC. When building an image,
which has to be flashed to different devices, an HMAC cannot
be used to sign file metadata, because the HMAC key should be
different on every device.

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Acked-by: Mimi Zohar <zohar@us.ibm.com>

1 files changed, 49 insertions, 17 deletions

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 5dd5b140242c..847a2d7dff17 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -26,34 +26,48 @@ static unsigned char evmkey[MAX_KEY_SIZE];
 static int evmkey_len = MAX_KEY_SIZE;
 
 struct crypto_shash *hmac_tfm;
+struct crypto_shash *hash_tfm;
 
-static struct shash_desc *init_desc(void)
+static struct shash_desc *init_desc(const char type)
 {
 	int rc;
+	char *algo;
+	struct crypto_shash **tfm;
 	struct shash_desc *desc;
 
-	if (hmac_tfm == NULL) {
-		hmac_tfm = crypto_alloc_shash(evm_hmac, 0, CRYPTO_ALG_ASYNC);
-		if (IS_ERR(hmac_tfm)) {
+	if (type == EVM_XATTR_HMAC) {
+		tfm = &hmac_tfm;
+		algo = evm_hmac;
+	} else {
+		tfm = &hash_tfm;
+		algo = evm_hash;
+	}
+
+	if (*tfm == NULL) {
+		*tfm = crypto_alloc_shash(algo, 0, CRYPTO_ALG_ASYNC);
+		if (IS_ERR(*tfm)) {
 			pr_err("Can not allocate %s (reason: %ld)\n",
-			       evm_hmac, PTR_ERR(hmac_tfm));
-			rc = PTR_ERR(hmac_tfm);
-			hmac_tfm = NULL;
+			       algo, PTR_ERR(*tfm));
+			rc = PTR_ERR(*tfm);
+			*tfm = NULL;
 			return ERR_PTR(rc);
 		}
 	}
 
-	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(hmac_tfm),
+	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
 			GFP_KERNEL);
 	if (!desc)
 		return ERR_PTR(-ENOMEM);
 
-	desc->tfm = hmac_tfm;
+	desc->tfm = *tfm;
 	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 
-	rc = crypto_shash_setkey(hmac_tfm, evmkey, evmkey_len);
-	if (rc)
-		goto out;
+	if (type == EVM_XATTR_HMAC) {
+		rc = crypto_shash_setkey(*tfm, evmkey, evmkey_len);
+		if (rc)
+			goto out;
+	}
+
 	rc = crypto_shash_init(desc);
 out:
 	if (rc) {
@@ -97,9 +111,11 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
  * the hmac using the requested xattr value. Don't alloc/free memory for
  * each xattr, but attempt to re-use the previously allocated memory.
  */
-int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
-		  const char *req_xattr_value, size_t req_xattr_value_len,
-		  char *digest)
+static int evm_calc_hmac_or_hash(struct dentry *dentry,
+				const char *req_xattr_name,
+				const char *req_xattr_value,
+				size_t req_xattr_value_len,
+				char type, char *digest)
 {
 	struct inode *inode = dentry->d_inode;
 	struct shash_desc *desc;
@@ -111,7 +127,7 @@ int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
 
 	if (!inode->i_op || !inode->i_op->getxattr)
 		return -EOPNOTSUPP;
-	desc = init_desc();
+	desc = init_desc(type);
 	if (IS_ERR(desc))
 		return PTR_ERR(desc);
 
@@ -145,6 +161,22 @@ out:
 	return error;
 }
 
+int evm_calc_hmac(struct dentry *dentry, const char *req_xattr_name,
+		  const char *req_xattr_value, size_t req_xattr_value_len,
+		  char *digest)
+{
+	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
+				req_xattr_value_len, EVM_XATTR_HMAC, digest);
+}
+
+int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
+		  const char *req_xattr_value, size_t req_xattr_value_len,
+		  char *digest)
+{
+	return evm_calc_hmac_or_hash(dentry, req_xattr_name, req_xattr_value,
+				req_xattr_value_len, IMA_XATTR_DIGEST, digest);
+}
+
 /*
  * Calculate the hmac and update security.evm xattr
  *
@@ -175,7 +207,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 {
 	struct shash_desc *desc;
 
-	desc = init_desc();
+	desc = init_desc(EVM_XATTR_HMAC);
 	if (IS_ERR(desc)) {
 		printk(KERN_INFO "init_desc failed\n");
 		return PTR_ERR(desc);