crypto: add "none" random provider

In case of not using random-number needing feature, it makes sense to
skip RNG init too. This is especially helpful when QEMU is sandboxed in
Stubdomain under Xen, where there is very little entropy so initial
getrandom() call delays the startup several seconds. In that setup, no
random bytes are needed at all.

Signed-off-by: Marek Marczykowski-Górecki <[email protected]>
Signed-off-by: Daniel P. Berrangé <[email protected]>

diff --git a/configure b/configure
index bb7fd12612459edcfdfd5fe43ece45a03617379d..997284e09411eb295302de5c986fa91954d3e65f 100755 (executable)
--- a/configure
+++ b/configure
@@ -509,6 +509,7 @@ libpmem=""
 default_devices="yes"
 plugins="no"
 fuzzing="no"
+rng_none="no"
 
 supported_cpu="no"
 supported_os="no"
@@ -1601,6 +1602,10 @@ for opt do
   ;;
   --gdb=*) gdb_bin="$optarg"
   ;;
+  --enable-rng-none) rng_none=yes
+  ;;
+  --disable-rng-none) rng_none=no
+  ;;
   *)
       echo "ERROR: unknown option $opt"
       echo "Try '$0 --help' for more information"
@@ -1898,6 +1903,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   debug-mutex     mutex debugging support
   libpmem         libpmem support
   xkbcommon       xkbcommon support
+  rng-none        dummy RNG, avoid using /dev/(u)random and getrandom()
 
 NOTE: The object files are built at the place where configure is launched
 EOF
@@ -6767,6 +6773,7 @@ echo "default devices   $default_devices"
 echo "plugin support    $plugins"
 echo "fuzzing support   $fuzzing"
 echo "gdb               $gdb_bin"
+echo "rng-none          $rng_none"
 
 if test "$supported_cpu" = "no"; then
     echo
@@ -7744,6 +7751,10 @@ if test "$edk2_blobs" = "yes" ; then
   echo "DECOMPRESS_EDK2_BLOBS=y" >> $config_host_mak
 fi
 
+if test "$rng_none" = "yes"; then
+  echo "CONFIG_RNG_NONE=y" >> $config_host_mak
+fi
+
 # use included Linux headers
 if test "$linux" = "yes" ; then
   mkdir -p linux-headers

diff --git a/crypto/Makefile.objs b/crypto/Makefile.objs
index c2a371b0b43c75b48c4f09c50fae230707be6b57..cdee92b4e59d9d77eb4977750a0ca94d418e27d4 100644 (file)
--- a/crypto/Makefile.objs
+++ b/crypto/Makefile.objs
@@ -35,5 +35,6 @@ crypto-obj-y += block-luks.o
 
 util-obj-$(CONFIG_GCRYPT) += random-gcrypt.o
 util-obj-$(if $(CONFIG_GCRYPT),n,$(CONFIG_GNUTLS)) += random-gnutls.o
-util-obj-$(if $(CONFIG_GCRYPT),n,$(if $(CONFIG_GNUTLS),n,y)) += random-platform.o
+util-obj-$(if $(CONFIG_GCRYPT),n,$(if $(CONFIG_GNUTLS),n,$(CONFIG_RNG_NONE))) += random-none.o
+util-obj-$(if $(CONFIG_GCRYPT),n,$(if $(CONFIG_GNUTLS),n,$(if $(CONFIG_RNG_NONE),n,y))) += random-platform.o
 util-obj-y += aes.o init.o

diff --git a/crypto/random-none.c b/crypto/random-none.c
new file mode 100644 (file)
index 0000000..102f8a4
--- /dev/null
+++ b/crypto/random-none.c
@@ -0,0 +1,38 @@
+/*
+ * QEMU Crypto "none" random number provider
+ *
+ * Copyright (c) 2020 Marek Marczykowski-Górecki
+ *                      <[email protected]>
+ *
+ * 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 "crypto/random.h"
+#include "qapi/error.h"
+
+int qcrypto_random_init(Error **errp)
+{
+    return 0;
+}
+
+int qcrypto_random_bytes(void *buf,
+                         size_t buflen,
+                         Error **errp)
+{
+    error_setg(errp, "Random bytes not available with \"none\" rng");
+    return -1;
+}