crypto: delete built-in XTS cipher mode support

The built-in AES+XTS implementation is used for the LUKS encryption
When building system emulators it is reasonable to expect that an
external crypto library is being used instead. The performance of the
builtin XTS implementation is terrible as it has no CPU acceleration
support. It is thus not worth keeping a home grown XTS implementation
for the built-in cipher backend.

Reviewed-by: Eric Blake <[email protected]>
Signed-off-by: Daniel P. Berrangé <[email protected]>

Author: berrange

crypto/cipher-builtin.c.inc

@@ -19,7 +19,6 @@
  */
 
 #include "crypto/aes.h"
-#include "crypto/xts.h"
 
 typedef struct QCryptoCipherBuiltinAESContext QCryptoCipherBuiltinAESContext;
 struct QCryptoCipherBuiltinAESContext {
@@ -31,7 +30,6 @@ typedef struct QCryptoCipherBuiltinAES QCryptoCipherBuiltinAES;
 struct QCryptoCipherBuiltinAES {
     QCryptoCipher base;
     QCryptoCipherBuiltinAESContext key;
-    QCryptoCipherBuiltinAESContext key_tweak;
     uint8_t iv[AES_BLOCK_SIZE];
 };
 
@@ -193,39 +191,6 @@ static int qcrypto_cipher_aes_decrypt_cbc(QCryptoCipher *cipher,
     return 0;
 }
 
-static int qcrypto_cipher_aes_encrypt_xts(QCryptoCipher *cipher,
-                                          const void *in, void *out,
-                                          size_t len, Error **errp)
-{
-    QCryptoCipherBuiltinAES *ctx
-        = container_of(cipher, QCryptoCipherBuiltinAES, base);
-
-    if (!qcrypto_length_check(len, AES_BLOCK_SIZE, errp)) {
-        return -1;
-    }
-    xts_encrypt(&ctx->key, &ctx->key_tweak,
-                do_aes_encrypt_ecb, do_aes_decrypt_ecb,
-                ctx->iv, len, out, in);
-    return 0;
-}
-
-static int qcrypto_cipher_aes_decrypt_xts(QCryptoCipher *cipher,
-                                          const void *in, void *out,
-                                          size_t len, Error **errp)
-{
-    QCryptoCipherBuiltinAES *ctx
-        = container_of(cipher, QCryptoCipherBuiltinAES, base);
-
-    if (!qcrypto_length_check(len, AES_BLOCK_SIZE, errp)) {
-        return -1;
-    }
-    xts_decrypt(&ctx->key, &ctx->key_tweak,
-                do_aes_encrypt_ecb, do_aes_decrypt_ecb,
-                ctx->iv, len, out, in);
-    return 0;
-}
-
-
 static int qcrypto_cipher_aes_setiv(QCryptoCipher *cipher, const uint8_t *iv,
                              size_t niv, Error **errp)
 {
@@ -256,14 +221,6 @@ static const struct QCryptoCipherDriver qcrypto_cipher_aes_driver_cbc = {
     .cipher_free = qcrypto_cipher_ctx_free,
 };
 
-static const struct QCryptoCipherDriver qcrypto_cipher_aes_driver_xts = {
-    .cipher_encrypt = qcrypto_cipher_aes_encrypt_xts,
-    .cipher_decrypt = qcrypto_cipher_aes_decrypt_xts,
-    .cipher_setiv = qcrypto_cipher_aes_setiv,
-    .cipher_free = qcrypto_cipher_ctx_free,
-};
-
-
 bool qcrypto_cipher_supports(QCryptoCipherAlgorithm alg,
                              QCryptoCipherMode mode)
 {
@@ -274,7 +231,6 @@ bool qcrypto_cipher_supports(QCryptoCipherAlgorithm alg,
         switch (mode) {
         case QCRYPTO_CIPHER_MODE_ECB:
         case QCRYPTO_CIPHER_MODE_CBC:
-        case QCRYPTO_CIPHER_MODE_XTS:
             return true;
         default:
             return false;
@@ -310,29 +266,13 @@ static QCryptoCipher *qcrypto_cipher_ctx_new(QCryptoCipherAlgorithm alg,
             case QCRYPTO_CIPHER_MODE_CBC:
                 drv = &qcrypto_cipher_aes_driver_cbc;
                 break;
-            case QCRYPTO_CIPHER_MODE_XTS:
-                drv = &qcrypto_cipher_aes_driver_xts;
-                break;
             default:
                 goto bad_mode;
             }
 
             ctx = g_new0(QCryptoCipherBuiltinAES, 1);
             ctx->base.driver = drv;
 
-            if (mode == QCRYPTO_CIPHER_MODE_XTS) {
-                nkey /= 2;
-                if (AES_set_encrypt_key(key + nkey, nkey * 8,
-                                        &ctx->key_tweak.enc)) {
-                    error_setg(errp, "Failed to set encryption key");
-                    goto error;
-                }
-                if (AES_set_decrypt_key(key + nkey, nkey * 8,
-                                        &ctx->key_tweak.dec)) {
-                    error_setg(errp, "Failed to set decryption key");
-                    goto error;
-                }
-            }
             if (AES_set_encrypt_key(key, nkey * 8, &ctx->key.enc)) {
                 error_setg(errp, "Failed to set encryption key");
                 goto error;

crypto/meson.build

@@ -23,14 +23,14 @@ crypto_ss.add(files(
 
 if nettle.found()
   crypto_ss.add(nettle, files('hash-nettle.c', 'hmac-nettle.c', 'pbkdf-nettle.c'))
+  if xts == 'private'
+    crypto_ss.add(files('xts.c'))
+  endif
 elif gcrypt.found()
   crypto_ss.add(gcrypt, files('hash-gcrypt.c', 'hmac-gcrypt.c', 'pbkdf-gcrypt.c'))
 else
   crypto_ss.add(files('hash-glib.c', 'hmac-glib.c', 'pbkdf-stub.c'))
 endif
-if xts == 'private'
-  crypto_ss.add(files('xts.c'))
-endif
 
 crypto_ss.add(when: 'CONFIG_SECRET_KEYRING', if_true: files('secret_keyring.c'))
 crypto_ss.add(when: 'CONFIG_AF_ALG', if_true: files('afalg.c', 'cipher-afalg.c', 'hash-afalg.c'))

meson.build

@@ -826,24 +826,23 @@ endif
 # Nettle has priority over gcrypt
 gcrypt = not_found
 nettle = not_found
-xts = 'private'
+xts = 'none'
 if get_option('nettle').enabled() and get_option('gcrypt').enabled()
   error('Only one of gcrypt & nettle can be enabled')
 elif (not get_option('nettle').auto() or have_system) and not get_option('gcrypt').enabled()
   nettle = dependency('nettle', version: '>=3.4',
                       method: 'pkg-config',
                       required: get_option('nettle'),
                       kwargs: static_kwargs)
-  if nettle.found() and cc.has_header('nettle/xts.h', dependencies: nettle)
-    xts = 'nettle'
+  if nettle.found() and not cc.has_header('nettle/xts.h', dependencies: nettle)
+    xts = 'private'
   endif
 endif
 if (not get_option('gcrypt').auto() or have_system) and not nettle.found()
   gcrypt = dependency('libgcrypt', version: '>=1.8',
                          method: 'config-tool',
                          required: get_option('gcrypt'),
                          kwargs: static_kwargs)
-  xts = 'gcrypt'
   # Debian has removed -lgpg-error from libgcrypt-config
   # as it "spreads unnecessary dependencies" which in
   # turn breaks static builds...