evm: Propagate choice of HMAC algorithm in evm_crypto.c

hulk inclusion
category: feature
feature: IMA Digest Lists extension
bugzilla: 46797

-------------------------------------------------

Commit 5feeb611 ("evm: Allow non-SHA1 digital signatures") introduced
the possibility to use different hash algorithm for signatures, but kept
the algorithm for the HMAC hard-coded (SHA1). Switching to a different
algorithm for HMAC would require to change the code in different places.

This patch introduces a new global variable called evm_hash_algo, and
consistently uses it whenever EVM perform HMAC-related operations. It also
introduces a new kernel configuration option called CONFIG_EVM_DEFAULT_HASH
so that evm_hash_algo can be defined at kernel compilation time.
Signed-off-by: NRoberto Sassu <roberto.sassu@huawei.com>
Acked-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NTianxing Zhang <zhangtianxing3@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

security/integrity/evm/Kconfig

@@ -13,6 +13,38 @@ config EVM
 
 	  If you are unsure how to answer this question, answer N.
 
+choice
+	prompt "Default EVM hash algorithm"
+	default EVM_DEFAULT_HASH_SHA256
+	depends on EVM
+	help
+	   Select the default hash algorithm used for the HMAC.
+
+	config EVM_DEFAULT_HASH_SHA1
+		bool "SHA1 (default)"
+		depends on CRYPTO_SHA1=y
+
+	config EVM_DEFAULT_HASH_SHA256
+		bool "SHA256"
+		depends on CRYPTO_SHA256=y
+
+	config EVM_DEFAULT_HASH_SHA512
+		bool "SHA512"
+		depends on CRYPTO_SHA512=y
+
+	config EVM_DEFAULT_HASH_WP512
+		bool "WP512"
+		depends on CRYPTO_WP512=y
+endchoice
+
+config EVM_DEFAULT_HASH
+	string
+	depends on EVM
+	default "sha1" if EVM_DEFAULT_HASH_SHA1
+	default "sha256" if EVM_DEFAULT_HASH_SHA256
+	default "sha512" if EVM_DEFAULT_HASH_SHA512
+	default "wp512" if EVM_DEFAULT_HASH_WP512
+
 config EVM_ATTR_FSUUID
 	bool "FSUUID (version 2)"
 	default y

security/integrity/evm/evm.h

@@ -32,6 +32,7 @@ struct xattr_list {
 };
 
 extern int evm_initialized;
+extern enum hash_algo evm_hash_algo;
 
 #define EVM_ATTR_FSUUID		0x0001
 

security/integrity/evm/evm_crypto.c

@@ -33,7 +33,7 @@ static DEFINE_MUTEX(mutex);
 
 static unsigned long evm_set_key_flags;
 
-static const char evm_hmac[] = "hmac(sha1)";
+enum hash_algo evm_hash_algo __ro_after_init = HASH_ALGO_SHA1;
 
 /**
  * evm_set_key() - set EVM HMAC key from the kernel
@@ -74,8 +74,12 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
 	long rc;
 	const char *algo;
 	struct crypto_shash **tfm, *tmp_tfm = NULL;
+	char evm_hmac[CRYPTO_MAX_ALG_NAME];
 	struct shash_desc *desc;
 
+	snprintf(evm_hmac, sizeof(evm_hmac), "hmac(%s)",
+		 CONFIG_EVM_DEFAULT_HASH);
+
 	if (type == EVM_XATTR_HMAC) {
 		if (!(evm_initialized & EVM_INIT_HMAC)) {
 			pr_err_once("HMAC key is not set\n");
@@ -320,14 +324,15 @@ int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
 	if (rc)
 		return -EPERM;
 
-	data.hdr.algo = HASH_ALGO_SHA1;
+	data.hdr.algo = evm_hash_algo;
 	rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 			   xattr_value_len, &data);
 	if (rc == 0) {
 		data.hdr.xattr.sha1.type = EVM_XATTR_HMAC;
 		rc = __vfs_setxattr_noperm(dentry, XATTR_NAME_EVM,
 					   &data.hdr.xattr.data[1],
-					   SHA1_DIGEST_SIZE + 1, 0);
+					   hash_digest_size[evm_hash_algo] + 1,
+					   0);
 	} else if (rc == -ENODATA && (inode->i_opflags & IOP_XATTR)) {
 		rc = __vfs_removexattr(dentry, XATTR_NAME_EVM);
 	}
@@ -339,7 +344,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 {
 	struct shash_desc *desc;
 
-	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
+	desc = init_desc(EVM_XATTR_HMAC, evm_hash_algo);
 	if (IS_ERR(desc)) {
 		pr_info("init_desc failed\n");
 		return PTR_ERR(desc);
@@ -352,7 +357,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
 }
 
 /*
- * Get the key from the TPM for the SHA1-HMAC
+ * Get the key from the TPM for the HMAC
  */
 int evm_init_key(void)
 {

security/integrity/evm/evm_main.c

@@ -213,17 +213,17 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 	/* check value type */
 	switch (xattr_data->type) {
 	case EVM_XATTR_HMAC:
-		if (xattr_len != sizeof(struct evm_xattr)) {
+		if (xattr_len != hash_digest_size[evm_hash_algo] + 1) {
 			evm_status = INTEGRITY_FAIL;
 			goto out;
 		}
-		digest.hdr.algo = HASH_ALGO_SHA1;
+		digest.hdr.algo = evm_hash_algo;
 		rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
 				   xattr_value_len, &digest);
 		if (rc)
 			break;
 		rc = crypto_memneq(xattr_data->data, digest.digest,
-				   SHA1_DIGEST_SIZE);
+				   hash_digest_size[evm_hash_algo]);
 		if (rc)
 			rc = -EINVAL;
 		break;
@@ -780,7 +780,7 @@ int evm_inode_init_security(struct inode *inode,
 		goto out;
 
 	evm_xattr->value = xattr_data;
-	evm_xattr->value_len = sizeof(*xattr_data);
+	evm_xattr->value_len = hash_digest_size[evm_hash_algo] + 1;
 	evm_xattr->name = XATTR_EVM_SUFFIX;
 	return 0;
 out:
@@ -802,9 +802,14 @@ void __init evm_load_x509(void)
 
 static int __init init_evm(void)
 {
-	int error;
+	int error, i;
 	struct list_head *pos, *q;
 
+	i = match_string(hash_algo_name, HASH_ALGO__LAST,
+			 CONFIG_EVM_DEFAULT_HASH);
+	if (i >= 0)
+		evm_hash_algo = i;
+
 	evm_init_config();
 
 	error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);

security/integrity/integrity.h

@@ -92,7 +92,7 @@ struct evm_ima_xattr_data {
 /* Only used in the EVM HMAC code. */
 struct evm_xattr {
 	struct evm_ima_xattr_data data;
-	u8 digest[SHA1_DIGEST_SIZE];
+	u8 digest[SHA512_DIGEST_SIZE];
 } __packed;
 
 #define IMA_MAX_DIGEST_SIZE	64