crypto: add support for nettle's native XTS impl

Nettle 3.5.0 will add support for the XTS mode. Use this because long
term we wish to delete QEMU's XTS impl to avoid carrying private crypto
algorithm impls.

Unfortunately this degrades nettle performance from 612 MB/s to 568 MB/s
as nettle's XTS impl isn't so well optimized yet.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

crypto-add-support-for-nettle-s-native-XTS-impl.patch

@@ -0,0 +1,126 @@
+From c4db6fcb2c45b800cd46e088f8265ccc0631b6fc Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= <berrange@redhat.com>
+Date: Mon, 14 Oct 2019 17:28:27 +0100
+Subject: [PATCH] crypto: add support for nettle's native XTS impl
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+Nettle 3.5.0 will add support for the XTS mode. Use this because long
+term we wish to delete QEMU's XTS impl to avoid carrying private crypto
+algorithm impls.
+
+Unfortunately this degrades nettle performance from 612 MB/s to 568 MB/s
+as nettle's XTS impl isn't so well optimized yet.
+
+Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
+Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
+Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
+---
+ configure              | 18 ++++++++++++++++++
+ crypto/cipher-nettle.c | 18 ++++++++++++++++++
+ 2 files changed, 36 insertions(+)
+
+diff --git a/configure b/configure
+index 577533e9ed..5dcaac3b95 100755
+--- a/configure
++++ b/configure
+@@ -473,6 +473,7 @@ gtk_gl="no"
+ tls_priority="NORMAL"
+ gnutls=""
+ nettle=""
++nettle_xts="no"
+ gcrypt=""
+ gcrypt_hmac="no"
+ auth_pam=""
+@@ -2918,6 +2919,19 @@ if test "$nettle" != "no"; then
+             pass="yes"
+         fi
+     fi
++    if test "$pass" = "yes"
++    then
++        cat > $TMPC << EOF
++#include <nettle/xts.h>
++int main(void) {
++  return 0;
++}
++EOF
++        if compile_prog "$nettle_cflags" "$nettle_libs" ; then
++            nettle_xts=yes
++            qemu_private_xts=no
++        fi
++    fi
+     if test "$pass" = "no" && test "$nettle" = "yes"; then
+         feature_not_found "nettle" "Install nettle devel >= 2.7.1"
+     else
+@@ -6391,6 +6405,10 @@ echo "TLS priority      $tls_priority"
+ echo "GNUTLS support    $gnutls"
+ echo "libgcrypt         $gcrypt"
+ echo "nettle            $nettle $(echo_version $nettle $nettle_version)"
++if test "$nettle" = "yes"
++then
++   echo "  XTS             $nettle_xts"
++fi
+ echo "libtasn1          $tasn1"
+ echo "PAM               $auth_pam"
+ echo "iconv support     $iconv"
+diff --git a/crypto/cipher-nettle.c b/crypto/cipher-nettle.c
+index d7411bb8ff..7e9a4cc199 100644
+--- a/crypto/cipher-nettle.c
++++ b/crypto/cipher-nettle.c
+@@ -19,7 +19,9 @@
+  */
+ 
+ #include "qemu/osdep.h"
++#ifdef CONFIG_QEMU_PRIVATE_XTS
+ #include "crypto/xts.h"
++#endif
+ #include "cipherpriv.h"
+ 
+ #include <nettle/nettle-types.h>
+@@ -30,6 +32,9 @@
+ #include <nettle/serpent.h>
+ #include <nettle/twofish.h>
+ #include <nettle/ctr.h>
++#ifndef CONFIG_QEMU_PRIVATE_XTS
++#include <nettle/xts.h>
++#endif
+ 
+ typedef void (*QCryptoCipherNettleFuncWrapper)(const void *ctx,
+                                                size_t length,
+@@ -626,9 +631,15 @@ qcrypto_nettle_cipher_encrypt(QCryptoCipher *cipher,
+         break;
+ 
+     case QCRYPTO_CIPHER_MODE_XTS:
++#ifdef CONFIG_QEMU_PRIVATE_XTS
+         xts_encrypt(ctx->ctx, ctx->ctx_tweak,
+                     ctx->alg_encrypt_wrapper, ctx->alg_encrypt_wrapper,
+                     ctx->iv, len, out, in);
++#else
++        xts_encrypt_message(ctx->ctx, ctx->ctx_tweak,
++                            ctx->alg_encrypt_native,
++                            ctx->iv, len, out, in);
++#endif
+         break;
+ 
+     case QCRYPTO_CIPHER_MODE_CTR:
+@@ -673,9 +684,16 @@ qcrypto_nettle_cipher_decrypt(QCryptoCipher *cipher,
+         break;
+ 
+     case QCRYPTO_CIPHER_MODE_XTS:
++#ifdef CONFIG_QEMU_PRIVATE_XTS
+         xts_decrypt(ctx->ctx, ctx->ctx_tweak,
+                     ctx->alg_encrypt_wrapper, ctx->alg_decrypt_wrapper,
+                     ctx->iv, len, out, in);
++#else
++        xts_decrypt_message(ctx->ctx, ctx->ctx_tweak,
++                            ctx->alg_decrypt_native,
++                            ctx->alg_encrypt_native,
++                            ctx->iv, len, out, in);
++#endif
+         break;
+     case QCRYPTO_CIPHER_MODE_CTR:
+         ctr_crypt(ctx->ctx, ctx->alg_encrypt_native,
+-- 
+2.27.0
+