crypto: add support for PBKDF2 algorithm

The LUKS data format includes use of PBKDF2 (Password-Based
Key Derivation Function). The Nettle library can provide
an implementation of this, but we don't want code directly
depending on a specific crypto library backend. Introduce
a new include/crypto/pbkdf.h header which defines a QEMU
API for invoking PBKDK2. The initial implementations are
backed by nettle & gcrypt, which are commonly available
with distros shipping GNUTLS.

The test suite data is taken from the cryptsetup codebase
under the LGPLv2.1+ license. This merely aims to verify
that whatever backend we provide for this function in QEMU
will comply with the spec.

Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
diff --git a/configure b/configure
index 71c1e2b..b88d0db 100755
--- a/configure
+++ b/configure
@@ -309,6 +309,7 @@
 gnutls_rnd=""
 nettle=""
 gcrypt=""
+gcrypt_kdf="no"
 vte=""
 virglrenderer=""
 tpm="yes"
@@ -2302,6 +2303,19 @@
         if test -z "$nettle"; then
            nettle="no"
         fi
+
+        cat > $TMPC << EOF
+#include <gcrypt.h>
+int main(void) {
+  gcry_kdf_derive(NULL, 0, GCRY_KDF_PBKDF2,
+                  GCRY_MD_SHA256,
+                  NULL, 0, 0, 0, NULL);
+ return 0;
+}
+EOF
+        if compile_prog "$gcrypt_cflags" "$gcrypt_libs" ; then
+            gcrypt_kdf=yes
+        fi
     else
         if test "$gcrypt" = "yes"; then
             feature_not_found "gcrypt" "Install gcrypt devel"
@@ -4726,6 +4740,7 @@
 echo "GNUTLS hash       $gnutls_hash"
 echo "GNUTLS rnd        $gnutls_rnd"
 echo "libgcrypt         $gcrypt"
+echo "libgcrypt kdf     $gcrypt_kdf"
 if test "$nettle" = "yes"; then
     echo "nettle            $nettle ($nettle_version)"
 else
@@ -5108,6 +5123,9 @@
 fi
 if test "$gcrypt" = "yes" ; then
   echo "CONFIG_GCRYPT=y" >> $config_host_mak
+  if test "$gcrypt_kdf" = "yes" ; then
+    echo "CONFIG_GCRYPT_KDF=y" >> $config_host_mak
+  fi
 fi
 if test "$nettle" = "yes" ; then
   echo "CONFIG_NETTLE=y" >> $config_host_mak