mkimage: Add support for signing with pkcs11

Add support for signing with the pkcs11 engine. This allows FIT images
to be signed with keys securely stored on a smartcard, hardware security
module, etc without exposing the keys.

Support for other engines can be added in the future by modifying
rsa_engine_get_pub_key() and rsa_engine_get_priv_key() to construct
correct key_id strings.

Signed-off-by: George McCollister <george.mccollister@gmail.com>

1 files changed, 233 insertions, 11 deletions

diff --git a/lib/rsa/rsa-sign.c b/lib/rsa/rsa-sign.c
index 9a09280013..8c6637e328 100644
--- a/lib/rsa/rsa-sign.c
+++ b/lib/rsa/rsa-sign.c
@@ -14,6 +14,7 @@
 #include <openssl/err.h>
 #include <openssl/ssl.h>
 #include <openssl/evp.h>
+#include <openssl/engine.h>
 
 #if OPENSSL_VERSION_NUMBER >= 0x10000000L
 #define HAVE_ERR_REMOVE_THREAD_STATE
@@ -31,14 +32,14 @@ static int rsa_err(const char *msg)
 }
 
 /**
- * rsa_get_pub_key() - read a public key from a .crt file
+ * rsa_pem_get_pub_key() - read a public key from a .crt file
  *
  * @keydir:	Directory containins the key
  * @name	Name of key file (will have a .crt extension)
  * @rsap	Returns RSA object, or NULL on failure
  * @return 0 if ok, -ve on error (in which case *rsap will be set to NULL)
  */
-static int rsa_get_pub_key(const char *keydir, const char *name, RSA **rsap)
+static int rsa_pem_get_pub_key(const char *keydir, const char *name, RSA **rsap)
 {
 	char path[1024];
 	EVP_PKEY *key;
@@ -96,14 +97,90 @@ err_cert:
 }
 
 /**
- * rsa_get_priv_key() - read a private key from a .key file
+ * rsa_engine_get_pub_key() - read a public key from given engine
  *
- * @keydir:	Directory containins the key
+ * @keydir:	Key prefix
+ * @name	Name of key
+ * @engine	Engine to use
+ * @rsap	Returns RSA object, or NULL on failure
+ * @return 0 if ok, -ve on error (in which case *rsap will be set to NULL)
+ */
+static int rsa_engine_get_pub_key(const char *keydir, const char *name,
+				  ENGINE *engine, RSA **rsap)
+{
+	const char *engine_id;
+	char key_id[1024];
+	EVP_PKEY *key;
+	RSA *rsa;
+	int ret;
+
+	*rsap = NULL;
+
+	engine_id = ENGINE_get_id(engine);
+
+	if (engine_id && !strcmp(engine_id, "pkcs11")) {
+		if (keydir)
+			snprintf(key_id, sizeof(key_id),
+				 "pkcs11:%s;object=%s;type=public",
+				 keydir, name);
+		else
+			snprintf(key_id, sizeof(key_id),
+				 "pkcs11:object=%s;type=public",
+				 name);
+	} else {
+		fprintf(stderr, "Engine not supported\n");
+		return -ENOTSUP;
+	}
+
+	key = ENGINE_load_public_key(engine, key_id, NULL, NULL);
+	if (!key)
+		return rsa_err("Failure loading public key from engine");
+
+	/* Convert to a RSA_style key. */
+	rsa = EVP_PKEY_get1_RSA(key);
+	if (!rsa) {
+		rsa_err("Couldn't convert to a RSA style key");
+		ret = -EINVAL;
+		goto err_rsa;
+	}
+
+	EVP_PKEY_free(key);
+	*rsap = rsa;
+
+	return 0;
+
+err_rsa:
+	EVP_PKEY_free(key);
+	return ret;
+}
+
+/**
+ * rsa_get_pub_key() - read a public key
+ *
+ * @keydir:	Directory containing the key (PEM file) or key prefix (engine)
+ * @name	Name of key file (will have a .crt extension)
+ * @engine	Engine to use
+ * @rsap	Returns RSA object, or NULL on failure
+ * @return 0 if ok, -ve on error (in which case *rsap will be set to NULL)
+ */
+static int rsa_get_pub_key(const char *keydir, const char *name,
+			   ENGINE *engine, RSA **rsap)
+{
+	if (engine)
+		return rsa_engine_get_pub_key(keydir, name, engine, rsap);
+	return rsa_pem_get_pub_key(keydir, name, rsap);
+}
+
+/**
+ * rsa_pem_get_priv_key() - read a private key from a .key file
+ *
+ * @keydir:	Directory containing the key
  * @name	Name of key file (will have a .key extension)
  * @rsap	Returns RSA object, or NULL on failure
  * @return 0 if ok, -ve on error (in which case *rsap will be set to NULL)
  */
-static int rsa_get_priv_key(const char *keydir, const char *name, RSA **rsap)
+static int rsa_pem_get_priv_key(const char *keydir, const char *name,
+				RSA **rsap)
 {
 	char path[1024];
 	RSA *rsa;
@@ -130,6 +207,81 @@ static int rsa_get_priv_key(const char *keydir, const char *name, RSA **rsap)
 	return 0;
 }
 
+/**
+ * rsa_engine_get_priv_key() - read a private key from given engine
+ *
+ * @keydir:	Key prefix
+ * @name	Name of key
+ * @engine	Engine to use
+ * @rsap	Returns RSA object, or NULL on failure
+ * @return 0 if ok, -ve on error (in which case *rsap will be set to NULL)
+ */
+static int rsa_engine_get_priv_key(const char *keydir, const char *name,
+				   ENGINE *engine, RSA **rsap)
+{
+	const char *engine_id;
+	char key_id[1024];
+	EVP_PKEY *key;
+	RSA *rsa;
+	int ret;
+
+	*rsap = NULL;
+
+	engine_id = ENGINE_get_id(engine);
+
+	if (engine_id && !strcmp(engine_id, "pkcs11")) {
+		if (keydir)
+			snprintf(key_id, sizeof(key_id),
+				 "pkcs11:%s;object=%s;type=private",
+				 keydir, name);
+		else
+			snprintf(key_id, sizeof(key_id),
+				 "pkcs11:object=%s;type=private",
+				 name);
+	} else {
+		fprintf(stderr, "Engine not supported\n");
+		return -ENOTSUP;
+	}
+
+	key = ENGINE_load_private_key(engine, key_id, NULL, NULL);
+	if (!key)
+		return rsa_err("Failure loading private key from engine");
+
+	/* Convert to a RSA_style key. */
+	rsa = EVP_PKEY_get1_RSA(key);
+	if (!rsa) {
+		rsa_err("Couldn't convert to a RSA style key");
+		ret = -EINVAL;
+		goto err_rsa;
+	}
+
+	EVP_PKEY_free(key);
+	*rsap = rsa;
+
+	return 0;
+
+err_rsa:
+	EVP_PKEY_free(key);
+	return ret;
+}
+
+/**
+ * rsa_get_priv_key() - read a private key
+ *
+ * @keydir:	Directory containing the key (PEM file) or key prefix (engine)
+ * @name	Name of key
+ * @engine	Engine to use for signing
+ * @rsap	Returns RSA object, or NULL on failure
+ * @return 0 if ok, -ve on error (in which case *rsap will be set to NULL)
+ */
+static int rsa_get_priv_key(const char *keydir, const char *name,
+			    ENGINE *engine, RSA **rsap)
+{
+	if (engine)
+		return rsa_engine_get_priv_key(keydir, name, engine, rsap);
+	return rsa_pem_get_priv_key(keydir, name, rsap);
+}
+
 static int rsa_init(void)
 {
 	int ret;
@@ -148,6 +300,45 @@ static int rsa_init(void)
 	return 0;
 }
 
+static int rsa_engine_init(const char *engine_id, ENGINE **pe)
+{
+	ENGINE *e;
+	int ret;
+
+	ENGINE_load_builtin_engines();
+
+	e = ENGINE_by_id(engine_id);
+	if (!e) {
+		fprintf(stderr, "Engine isn't available\n");
+		ret = -1;
+		goto err_engine_by_id;
+	}
+
+	if (!ENGINE_init(e)) {
+		fprintf(stderr, "Couldn't initialize engine\n");
+		ret = -1;
+		goto err_engine_init;
+	}
+
+	if (!ENGINE_set_default_RSA(e)) {
+		fprintf(stderr, "Couldn't set engine as default for RSA\n");
+		ret = -1;
+		goto err_set_rsa;
+	}
+
+	*pe = e;
+
+	return 0;
+
+err_set_rsa:
+	ENGINE_finish(e);
+err_engine_init:
+	ENGINE_free(e);
+err_engine_by_id:
+	ENGINE_cleanup();
+	return ret;
+}
+
 static void rsa_remove(void)
 {
 	CRYPTO_cleanup_all_ex_data();
@@ -160,6 +351,14 @@ static void rsa_remove(void)
 	EVP_cleanup();
 }
 
+static void rsa_engine_remove(ENGINE *e)
+{
+	if (e) {
+		ENGINE_finish(e);
+		ENGINE_free(e);
+	}
+}
+
 static int rsa_sign_with_key(RSA *rsa, struct checksum_algo *checksum_algo,
 		const struct image_region region[], int region_count,
 		uint8_t **sigp, uint *sig_size)
@@ -235,13 +434,20 @@ int rsa_sign(struct image_sign_info *info,
 	     uint8_t **sigp, uint *sig_len)
 {
 	RSA *rsa;
+	ENGINE *e = NULL;
 	int ret;
 
 	ret = rsa_init();
 	if (ret)
 		return ret;
 
-	ret = rsa_get_priv_key(info->keydir, info->keyname, &rsa);
+	if (info->engine_id) {
+		ret = rsa_engine_init(info->engine_id, &e);
+		if (ret)
+			goto err_engine;
+	}
+
+	ret = rsa_get_priv_key(info->keydir, info->keyname, e, &rsa);
 	if (ret)
 		goto err_priv;
 	ret = rsa_sign_with_key(rsa, info->checksum, region,
@@ -250,6 +456,8 @@ int rsa_sign(struct image_sign_info *info,
 		goto err_sign;
 
 	RSA_free(rsa);
+	if (info->engine_id)
+		rsa_engine_remove(e);
 	rsa_remove();
 
 	return ret;
@@ -257,6 +465,9 @@ int rsa_sign(struct image_sign_info *info,
 err_sign:
 	RSA_free(rsa);
 err_priv:
+	if (info->engine_id)
+		rsa_engine_remove(e);
+err_engine:
 	rsa_remove();
 	return ret;
 }
@@ -446,14 +657,20 @@ int rsa_add_verify_data(struct image_sign_info *info, void *keydest)
 	int ret;
 	int bits;
 	RSA *rsa;
+	ENGINE *e = NULL;
 
 	debug("%s: Getting verification data\n", __func__);
-	ret = rsa_get_pub_key(info->keydir, info->keyname, &rsa);
+	if (info->engine_id) {
+		ret = rsa_engine_init(info->engine_id, &e);
+		if (ret)
+			return ret;
+	}
+	ret = rsa_get_pub_key(info->keydir, info->keyname, e, &rsa);
 	if (ret)
-		return ret;
+		goto err_get_pub_key;
 	ret = rsa_get_params(rsa, &exponent, &n0_inv, &modulus, &r_squared);
 	if (ret)
-		return ret;
+		goto err_get_params;
 	bits = BN_num_bits(modulus);
 	parent = fdt_subnode_offset(keydest, 0, FIT_SIG_NODENAME);
 	if (parent == -FDT_ERR_NOTFOUND) {
@@ -518,7 +735,12 @@ done:
 	BN_free(modulus);
 	BN_free(r_squared);
 	if (ret)
-		return ret == -FDT_ERR_NOSPACE ? -ENOSPC : -EIO;
+		ret = ret == -FDT_ERR_NOSPACE ? -ENOSPC : -EIO;
+err_get_params:
+	RSA_free(rsa);
+err_get_pub_key:
+	if (info->engine_id)
+		rsa_engine_remove(e);
 
-	return 0;
+	return ret;
 }