crypto: add gnutls cipher provider

Add an implementation of the QEMU cipher APIs to the gnutls
crypto backend. XTS support is only available for gnutls
version >= 3.6.8. Since ECB mode is not exposed by gnutls
APIs, we can't use the private XTS code for compatibility.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

crypto/cipher-gnutls.c.inc

@@ -0,0 +1,335 @@
+/*
+ * QEMU Crypto cipher gnutls algorithms
+ *
+ * Copyright (c) 2021 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "cipherpriv.h"
+
+#include <gnutls/crypto.h>
+
+#if GNUTLS_VERSION_NUMBER >= 0x030608
+#define QEMU_GNUTLS_XTS
+#endif
+
+bool qcrypto_cipher_supports(QCryptoCipherAlgorithm alg,
+                             QCryptoCipherMode mode)
+{
+
+    switch (mode) {
+    case QCRYPTO_CIPHER_MODE_ECB:
+    case QCRYPTO_CIPHER_MODE_CBC:
+        switch (alg) {
+        case QCRYPTO_CIPHER_ALG_AES_128:
+        case QCRYPTO_CIPHER_ALG_AES_192:
+        case QCRYPTO_CIPHER_ALG_AES_256:
+        case QCRYPTO_CIPHER_ALG_DES:
+        case QCRYPTO_CIPHER_ALG_3DES:
+            return true;
+        default:
+            return false;
+        }
+#ifdef QEMU_GNUTLS_XTS
+    case QCRYPTO_CIPHER_MODE_XTS:
+        switch (alg) {
+        case QCRYPTO_CIPHER_ALG_AES_128:
+        case QCRYPTO_CIPHER_ALG_AES_256:
+            return true;
+        default:
+            return false;
+        }
+#endif
+    default:
+        return false;
+    }
+}
+
+typedef struct QCryptoCipherGnutls QCryptoCipherGnutls;
+struct QCryptoCipherGnutls {
+    QCryptoCipher base;
+    gnutls_cipher_hd_t handle; /* XTS & CBC mode */
+    gnutls_cipher_algorithm_t galg; /* ECB mode */
+    guint8 *key; /* ECB mode */
+    size_t nkey; /* ECB mode */
+    size_t blocksize;
+};
+
+
+static void
+qcrypto_gnutls_cipher_free(QCryptoCipher *cipher)
+{
+    QCryptoCipherGnutls *ctx = container_of(cipher, QCryptoCipherGnutls, base);
+
+    g_free(ctx->key);
+    if (ctx->handle) {
+        gnutls_cipher_deinit(ctx->handle);
+    }
+    g_free(ctx);
+}
+
+
+static int
+qcrypto_gnutls_cipher_encrypt(QCryptoCipher *cipher,
+                              const void *in,
+                              void *out,
+                              size_t len,
+                              Error **errp)
+{
+    QCryptoCipherGnutls *ctx = container_of(cipher, QCryptoCipherGnutls, base);
+    int err;
+
+    if (len % ctx->blocksize) {
+        error_setg(errp, "Length %zu must be a multiple of block size %zu",
+                   len, ctx->blocksize);
+        return -1;
+    }
+
+    if (ctx->handle) { /* CBC / XTS mode */
+        err = gnutls_cipher_encrypt2(ctx->handle,
+                                     in, len,
+                                     out, len);
+        if (err != 0) {
+            error_setg(errp, "Cannot encrypt data: %s",
+                       gnutls_strerror(err));
+            return -1;
+        }
+    } else { /* ECB mode very inefficiently faked with CBC */
+        g_autofree unsigned char *iv = g_new0(unsigned char, ctx->blocksize);
+        while (len) {
+            gnutls_cipher_hd_t handle;
+            gnutls_datum_t gkey = { (unsigned char *)ctx->key, ctx->nkey };
+            int err = gnutls_cipher_init(&handle, ctx->galg, &gkey, NULL);
+            if (err != 0) {
+                error_setg(errp, "Cannot initialize cipher: %s",
+                           gnutls_strerror(err));
+                return -1;
+            }
+
+            gnutls_cipher_set_iv(handle, iv, ctx->blocksize);
+
+            err = gnutls_cipher_encrypt2(handle,
+                                         in, ctx->blocksize,
+                                         out, ctx->blocksize);
+            if (err != 0) {
+                gnutls_cipher_deinit(handle);
+                error_setg(errp, "Cannot encrypt data: %s",
+                           gnutls_strerror(err));
+                return -1;
+            }
+            gnutls_cipher_deinit(handle);
+
+            len -= ctx->blocksize;
+            in += ctx->blocksize;
+            out += ctx->blocksize;
+        }
+    }
+
+    return 0;
+}
+
+
+static int
+qcrypto_gnutls_cipher_decrypt(QCryptoCipher *cipher,
+                              const void *in,
+                              void *out,
+                              size_t len,
+                              Error **errp)
+{
+    QCryptoCipherGnutls *ctx = container_of(cipher, QCryptoCipherGnutls, base);
+    int err;
+
+    if (len % ctx->blocksize) {
+        error_setg(errp, "Length %zu must be a multiple of block size %zu",
+                   len, ctx->blocksize);
+        return -1;
+    }
+
+    if (ctx->handle) { /* CBC / XTS mode */
+        err = gnutls_cipher_decrypt2(ctx->handle,
+                                     in, len,
+                                     out, len);
+
+        if (err != 0) {
+            error_setg(errp, "Cannot decrypt data: %s",
+                       gnutls_strerror(err));
+            return -1;
+        }
+    } else { /* ECB mode very inefficiently faked with CBC */
+        g_autofree unsigned char *iv = g_new0(unsigned char, ctx->blocksize);
+        while (len) {
+            gnutls_cipher_hd_t handle;
+            gnutls_datum_t gkey = { (unsigned char *)ctx->key, ctx->nkey };
+            int err = gnutls_cipher_init(&handle, ctx->galg, &gkey, NULL);
+            if (err != 0) {
+                error_setg(errp, "Cannot initialize cipher: %s",
+                           gnutls_strerror(err));
+                return -1;
+            }
+
+            gnutls_cipher_set_iv(handle, iv, ctx->blocksize);
+
+            err = gnutls_cipher_decrypt2(handle,
+                                         in, ctx->blocksize,
+                                         out, ctx->blocksize);
+            if (err != 0) {
+                gnutls_cipher_deinit(handle);
+                error_setg(errp, "Cannot encrypt data: %s",
+                           gnutls_strerror(err));
+                return -1;
+            }
+            gnutls_cipher_deinit(handle);
+
+            len -= ctx->blocksize;
+            in += ctx->blocksize;
+            out += ctx->blocksize;
+        }
+    }
+
+    return 0;
+}
+
+static int
+qcrypto_gnutls_cipher_setiv(QCryptoCipher *cipher,
+                            const uint8_t *iv, size_t niv,
+                            Error **errp)
+{
+    QCryptoCipherGnutls *ctx = container_of(cipher, QCryptoCipherGnutls, base);
+
+    if (niv != ctx->blocksize) {
+        error_setg(errp, "Expected IV size %zu not %zu",
+                   ctx->blocksize, niv);
+        return -1;
+    }
+
+    gnutls_cipher_set_iv(ctx->handle, (unsigned char *)iv, niv);
+
+    return 0;
+}
+
+
+static struct QCryptoCipherDriver gnutls_driver = {
+    .cipher_encrypt = qcrypto_gnutls_cipher_encrypt,
+    .cipher_decrypt = qcrypto_gnutls_cipher_decrypt,
+    .cipher_setiv = qcrypto_gnutls_cipher_setiv,
+    .cipher_free = qcrypto_gnutls_cipher_free,
+};
+
+static QCryptoCipher *qcrypto_cipher_ctx_new(QCryptoCipherAlgorithm alg,
+                                             QCryptoCipherMode mode,
+                                             const uint8_t *key,
+                                             size_t nkey,
+                                             Error **errp)
+{
+    QCryptoCipherGnutls *ctx;
+    gnutls_datum_t gkey = { (unsigned char *)key, nkey };
+    gnutls_cipher_algorithm_t galg = GNUTLS_CIPHER_UNKNOWN;
+    int err;
+
+    switch (mode) {
+#ifdef QEMU_GNUTLS_XTS
+    case QCRYPTO_CIPHER_MODE_XTS:
+        switch (alg) {
+        case QCRYPTO_CIPHER_ALG_AES_128:
+            galg = GNUTLS_CIPHER_AES_128_XTS;
+            break;
+        case QCRYPTO_CIPHER_ALG_AES_256:
+            galg = GNUTLS_CIPHER_AES_256_XTS;
+            break;
+        default:
+            break;
+        }
+        break;
+#endif
+
+    case QCRYPTO_CIPHER_MODE_ECB:
+    case QCRYPTO_CIPHER_MODE_CBC:
+        switch (alg) {
+        case QCRYPTO_CIPHER_ALG_AES_128:
+            galg = GNUTLS_CIPHER_AES_128_CBC;
+            break;
+        case QCRYPTO_CIPHER_ALG_AES_192:
+            galg = GNUTLS_CIPHER_AES_192_CBC;
+            break;
+        case QCRYPTO_CIPHER_ALG_AES_256:
+            galg = GNUTLS_CIPHER_AES_256_CBC;
+            break;
+        case QCRYPTO_CIPHER_ALG_DES:
+            galg = GNUTLS_CIPHER_DES_CBC;
+            break;
+        case QCRYPTO_CIPHER_ALG_3DES:
+            galg = GNUTLS_CIPHER_3DES_CBC;
+            break;
+        default:
+            break;
+        }
+        break;
+    default:
+        break;
+    }
+
+    if (galg == GNUTLS_CIPHER_UNKNOWN) {
+        error_setg(errp, "Unsupported cipher algorithm %s with %s mode",
+                   QCryptoCipherAlgorithm_str(alg),
+                   QCryptoCipherMode_str(mode));
+        return NULL;
+    }
+
+    if (!qcrypto_cipher_validate_key_length(alg, mode, nkey, errp)) {
+        return NULL;
+    }
+
+    ctx = g_new0(QCryptoCipherGnutls, 1);
+    ctx->base.driver = &gnutls_driver;
+
+    if (mode == QCRYPTO_CIPHER_MODE_ECB) {
+        ctx->key = g_new0(guint8, nkey);
+        memcpy(ctx->key, key, nkey);
+        ctx->nkey = nkey;
+        ctx->galg = galg;
+    } else {
+        err = gnutls_cipher_init(&ctx->handle, galg, &gkey, NULL);
+        if (err != 0) {
+            error_setg(errp, "Cannot initialize cipher: %s",
+                       gnutls_strerror(err));
+            goto error;
+        }
+    }
+
+    if (alg == QCRYPTO_CIPHER_ALG_DES ||
+        alg == QCRYPTO_CIPHER_ALG_3DES)
+        ctx->blocksize = 8;
+    else
+        ctx->blocksize = 16;
+
+    /*
+     * Our API contract for requires iv to be optional
+     * but nettle gets unhappy when called by gnutls
+     * in this case, so we just force set a default
+     * all-zeros IV, to match behaviour of other backends.
+     */
+    if (mode != QCRYPTO_CIPHER_MODE_ECB) {
+        g_autofree unsigned char *iv = g_new0(unsigned char, ctx->blocksize);
+        gnutls_cipher_set_iv(ctx->handle, iv, ctx->blocksize);
+    }
+
+    return &ctx->base;
+
+ error:
+    qcrypto_gnutls_cipher_free(&ctx->base);
+    return NULL;
+}

crypto/cipher.c

@@ -136,6 +136,8 @@ qcrypto_cipher_validate_key_length(QCryptoCipherAlgorithm alg,
 #include "cipher-gcrypt.c.inc"
 #elif defined CONFIG_NETTLE
 #include "cipher-nettle.c.inc"
+#elif defined CONFIG_GNUTLS_CRYPTO
+#include "cipher-gnutls.c.inc"
 #else
 #include "cipher-builtin.c.inc"
 #endif