[Qemu-devel] [PATCH v6 0/4] rng-builtin: add an RNG backend that uses qemu_guest_getrandom()

[Qemu-devel] [PATCH v6 0/4] rng-builtin: add an RNG backend that uses qemu_guest_getrandom()

[Laurent Vivier]

Add a new RNG backend using QEMU builtin getrandom function.

This patch applies on top of
    "[PATCH v8 00/24] Add qemu_getrandom and ARMv8.5-RNG etc"
Based-on: 20190517023924.1686-1-richard.henderson@linaro.org

v6: remove "sysemu/rng-random.h" from virtio-rng.c
    rebase on qemu_getrandom v8

v5: PATCH 1 s/linux/Linux/
    remove superfluous includes from rng-builtin.c
    don't update rng-random documentation
    add a patch from Markus to keep the default backend out of VirtIORNGConf
    move TYPE_RNG_BUILTIN to sysemu/rng.h and remove sysemu/rng-builtin.h

v4: update PATCH 1 commit message

v3: Include Kashyap's patch in the series
    Add a patch to change virtio-rng default backend to rng-builtin

v2: Update qemu-options.hx
    describe the new backend and specify virtio-rng uses the
    rng-random by default

Kashyap Chamarthy (1):
  VirtIO-RNG: Update default entropy source to `/dev/urandom`

Laurent Vivier (2):
  rng-builtin: add an RNG backend that uses qemu_guest_getrandom()
  virtio-rng: change default backend to rng-builtin

Markus Armbruster (1):
  virtio-rng: Keep the default backend out of VirtIORNGConf

 backends/Makefile.objs         |  2 +-
 backends/rng-builtin.c         | 53 ++++++++++++++++++++++++++++++++++
 backends/rng-random.c          |  2 +-
 hw/virtio/virtio-rng.c         | 19 +++++-------
 include/hw/virtio/virtio-rng.h |  2 --
 include/sysemu/rng.h           |  2 ++
 qemu-options.hx                |  9 +++++-
 7 files changed, 73 insertions(+), 16 deletions(-)
 create mode 100644 backends/rng-builtin.c

-- 
2.20.1

[Qemu-devel] [PATCH v6 1/4] VirtIO-RNG: Update default entropy source to `/dev/urandom`

[Laurent Vivier]

From: Kashyap Chamarthy <kchamart@redhat.com>

When QEMU exposes a VirtIO-RNG device to the guest, that device needs a
source of entropy, and that source needs to be "non-blocking", like
`/dev/urandom`.  However, currently QEMU defaults to the problematic
`/dev/random`, which on Linux is "blocking" (as in, it waits until
sufficient entropy is available).

Why prefer `/dev/urandom` over `/dev/random`?
---------------------------------------------

The man pages of urandom(4) and random(4) state:

    "The /dev/random device is a legacy interface which dates back to a
    time where the cryptographic primitives used in the implementation
    of /dev/urandom were not widely trusted.  It will return random
    bytes only within the estimated number of bits of fresh noise in the
    entropy pool, blocking if necessary.  /dev/random is suitable for
    applications that need high quality randomness, and can afford
    indeterminate delays."

Further, the "Usage" section of the said man pages state:

    "The /dev/random interface is considered a legacy interface, and
    /dev/urandom is preferred and sufficient in all use cases, with the
    exception of applications which require randomness during early boot
    time; for these applications, getrandom(2) must be used instead,
    because it will block until the entropy pool is initialized.

    "If a seed file is saved across reboots as recommended below (all
    major Linux distributions have done this since 2000 at least), the
    output is cryptographically secure against attackers without local
    root access as soon as it is reloaded in the boot sequence, and
    perfectly adequate for network encryption session keys.  Since reads
    from /dev/random may block, users will usually want to open it in
    nonblocking mode (or perform a read with timeout), and provide some
    sort of user notification if the desired entropy is not immediately
    available."

And refer to random(7) for a comparison of `/dev/random` and
`/dev/urandom`.

What about other OSes?
----------------------

`/dev/urandom` exists and works on OS-X, FreeBSD, DragonFlyBSD, NetBSD
and OpenBSD, which cover all the non-Linux platforms we explicitly
support, aside from Windows.

On Windows `/dev/random` doesn't work either so we don't regress.
This is actually another argument in favour of using the newly
proposed 'rng-builtin' backend by default, as that will work on
Windows.

    - - -

Given the above, change the entropy source for VirtIO-RNG device to
`/dev/urandom`.

Related discussion in these[1][2] past threads.

[1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html
    -- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?"
[2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html
    -- "[RFC] Virtio RNG: Consider changing the default entropy source to
       /dev/urandom"

Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 backends/rng-random.c | 2 +-
 qemu-options.hx       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/backends/rng-random.c b/backends/rng-random.c
index e2a49b0571d7..eff36ef14084 100644
--- a/backends/rng-random.c
+++ b/backends/rng-random.c
@@ -112,7 +112,7 @@ static void rng_random_init(Object *obj)
                             rng_random_set_filename,
                             NULL);
 
-    s->filename = g_strdup("/dev/random");
+    s->filename = g_strdup("/dev/urandom");
     s->fd = -1;
 }
 
diff --git a/qemu-options.hx b/qemu-options.hx
index 7ae3373a0094..73046f8274d1 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4326,7 +4326,7 @@ Creates a random number generator backend which obtains entropy from
 a device on the host. The @option{id} parameter is a unique ID that
 will be used to reference this entropy backend from the @option{virtio-rng}
 device. The @option{filename} parameter specifies which file to obtain
-entropy from and if omitted defaults to @option{/dev/random}.
+entropy from and if omitted defaults to @option{/dev/urandom}.
 
 @item -object rng-egd,id=@var{id},chardev=@var{chardevid}
 
-- 
2.20.1

[Qemu-devel] [PATCH v6 2/4] rng-builtin: add an RNG backend that uses qemu_guest_getrandom()

[Laurent Vivier]

Add a new RNG backend using QEMU builtin getrandom function.

It can be created and used with something like:

    ... -object rng-builtin,id=rng0 -device virtio-rng,rng=rng0 ...

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 backends/Makefile.objs |  2 +-
 backends/rng-builtin.c | 54 ++++++++++++++++++++++++++++++++++++++++++
 qemu-options.hx        |  7 ++++++
 3 files changed, 62 insertions(+), 1 deletion(-)
 create mode 100644 backends/rng-builtin.c

diff --git a/backends/Makefile.objs b/backends/Makefile.objs
index 981e8e122f2c..f0691116e86e 100644
--- a/backends/Makefile.objs
+++ b/backends/Makefile.objs
@@ -1,4 +1,4 @@
-common-obj-y += rng.o rng-egd.o
+common-obj-y += rng.o rng-egd.o rng-builtin.o
 common-obj-$(CONFIG_POSIX) += rng-random.o
 
 common-obj-$(CONFIG_TPM) += tpm.o
diff --git a/backends/rng-builtin.c b/backends/rng-builtin.c
new file mode 100644
index 000000000000..6b9543a7de87
--- /dev/null
+++ b/backends/rng-builtin.c
@@ -0,0 +1,54 @@
+/*
+ * QEMU Builtin Random Number Generator Backend
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "sysemu/rng.h"
+#include "qemu/main-loop.h"
+#include "qemu/guest-random.h"
+
+#define TYPE_RNG_BUILTIN "rng-builtin"
+#define RNG_BUILTIN(obj) OBJECT_CHECK(RngBuiltin, (obj), TYPE_RNG_BUILTIN)
+
+typedef struct RngBuiltin {
+    RngBackend parent;
+} RngBuiltin;
+
+static void rng_builtin_request_entropy(RngBackend *b, RngRequest *req)
+{
+    RngBuiltin *s = RNG_BUILTIN(b);
+
+    while (!QSIMPLEQ_EMPTY(&s->parent.requests)) {
+        RngRequest *req = QSIMPLEQ_FIRST(&s->parent.requests);
+
+        qemu_guest_getrandom_nofail(req->data, req->size);
+
+        req->receive_entropy(req->opaque, req->data, req->size);
+
+        rng_backend_finalize_request(&s->parent, req);
+    }
+}
+
+static void rng_builtin_class_init(ObjectClass *klass, void *data)
+{
+    RngBackendClass *rbc = RNG_BACKEND_CLASS(klass);
+
+    rbc->request_entropy = rng_builtin_request_entropy;
+}
+
+static const TypeInfo rng_builtin_info = {
+    .name = TYPE_RNG_BUILTIN,
+    .parent = TYPE_RNG_BACKEND,
+    .instance_size = sizeof(RngBuiltin),
+    .class_init = rng_builtin_class_init,
+};
+
+static void register_types(void)
+{
+    type_register_static(&rng_builtin_info);
+}
+
+type_init(register_types);
diff --git a/qemu-options.hx b/qemu-options.hx
index 73046f8274d1..d5233e189ceb 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4320,6 +4320,13 @@ other options.
 
 The @option{share} boolean option is @var{on} by default with memfd.
 
+@item -object rng-builtin,id=@var{id}
+
+Creates a random number generator backend which obtains entropy from
+QEMU builtin functions. The @option{id} parameter is a unique ID that
+will be used to reference this entropy backend from the @option{virtio-rng}
+device.
+
 @item -object rng-random,id=@var{id},filename=@var{/dev/random}
 
 Creates a random number generator backend which obtains entropy from
-- 
2.20.1

[Qemu-devel] [PATCH v6 3/4] virtio-rng: Keep the default backend out of VirtIORNGConf

[Laurent Vivier]

From: Markus Armbruster <armbru@redhat.com>

The default backend is only used within virtio_rng_device_realize().
Replace VirtIORNGConf member default_backend by a local variable.
Adjust its type to reduce conversions.

While there, pass &error_abort instead of NULL when failure would be a
programming error.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/virtio/virtio-rng.c         | 20 +++++++++-----------
 include/hw/virtio/virtio-rng.h |  2 --
 2 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
index 30493a258622..73ffb476e030 100644
--- a/hw/virtio/virtio-rng.c
+++ b/hw/virtio/virtio-rng.c
@@ -16,6 +16,7 @@
 #include "hw/virtio/virtio.h"
 #include "hw/virtio/virtio-rng.h"
 #include "sysemu/rng.h"
+#include "sysemu/rng-random.h"
 #include "qom/object_interfaces.h"
 #include "trace.h"
 
@@ -189,27 +190,24 @@ static void virtio_rng_device_realize(DeviceState *dev, Error **errp)
     }
 
     if (vrng->conf.rng == NULL) {
-        vrng->conf.default_backend = RNG_RANDOM(object_new(TYPE_RNG_RANDOM));
+        Object *default_backend = object_new(TYPE_RNG_RANDOM);
 
-        user_creatable_complete(USER_CREATABLE(vrng->conf.default_backend),
+        user_creatable_complete(USER_CREATABLE(default_backend),
                                 &local_err);
         if (local_err) {
             error_propagate(errp, local_err);
-            object_unref(OBJECT(vrng->conf.default_backend));
+            object_unref(default_backend);
             return;
         }
 
-        object_property_add_child(OBJECT(dev),
-                                  "default-backend",
-                                  OBJECT(vrng->conf.default_backend),
-                                  NULL);
+        object_property_add_child(OBJECT(dev), "default-backend",
+                                  default_backend, &error_abort);
 
         /* The child property took a reference, we can safely drop ours now */
-        object_unref(OBJECT(vrng->conf.default_backend));
+        object_unref(default_backend);
 
-        object_property_set_link(OBJECT(dev),
-                                 OBJECT(vrng->conf.default_backend),
-                                 "rng", NULL);
+        object_property_set_link(OBJECT(dev), default_backend,
+                                 "rng", &error_abort);
     }
 
     vrng->rng = vrng->conf.rng;
diff --git a/include/hw/virtio/virtio-rng.h b/include/hw/virtio/virtio-rng.h
index 922dce7caccf..28ff752c4096 100644
--- a/include/hw/virtio/virtio-rng.h
+++ b/include/hw/virtio/virtio-rng.h
@@ -13,7 +13,6 @@
 #define QEMU_VIRTIO_RNG_H
 
 #include "sysemu/rng.h"
-#include "sysemu/rng-random.h"
 #include "standard-headers/linux/virtio_rng.h"
 
 #define TYPE_VIRTIO_RNG "virtio-rng-device"
@@ -26,7 +25,6 @@ struct VirtIORNGConf {
     RngBackend *rng;
     uint64_t max_bytes;
     uint32_t period_ms;
-    RngRandom *default_backend;
 };
 
 typedef struct VirtIORNG {
-- 
2.20.1

[Qemu-devel] [PATCH v6 4/4] virtio-rng: change default backend to rng-builtin

[Laurent Vivier]

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 backends/rng-builtin.c | 1 -
 hw/virtio/virtio-rng.c | 3 +--
 include/sysemu/rng.h   | 2 ++
 qemu-options.hx        | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/backends/rng-builtin.c b/backends/rng-builtin.c
index 6b9543a7de87..868055cbc723 100644
--- a/backends/rng-builtin.c
+++ b/backends/rng-builtin.c
@@ -10,7 +10,6 @@
 #include "qemu/main-loop.h"
 #include "qemu/guest-random.h"
 
-#define TYPE_RNG_BUILTIN "rng-builtin"
 #define RNG_BUILTIN(obj) OBJECT_CHECK(RngBuiltin, (obj), TYPE_RNG_BUILTIN)
 
 typedef struct RngBuiltin {
diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
index 73ffb476e030..55745f75a1c9 100644
--- a/hw/virtio/virtio-rng.c
+++ b/hw/virtio/virtio-rng.c
@@ -16,7 +16,6 @@
 #include "hw/virtio/virtio.h"
 #include "hw/virtio/virtio-rng.h"
 #include "sysemu/rng.h"
-#include "sysemu/rng-random.h"
 #include "qom/object_interfaces.h"
 #include "trace.h"
 
@@ -190,7 +189,7 @@ static void virtio_rng_device_realize(DeviceState *dev, Error **errp)
     }
 
     if (vrng->conf.rng == NULL) {
-        Object *default_backend = object_new(TYPE_RNG_RANDOM);
+        Object *default_backend = object_new(TYPE_RNG_BUILTIN);
 
         user_creatable_complete(USER_CREATABLE(default_backend),
                                 &local_err);
diff --git a/include/sysemu/rng.h b/include/sysemu/rng.h
index 27b37da05d2e..9dc5e0e90100 100644
--- a/include/sysemu/rng.h
+++ b/include/sysemu/rng.h
@@ -24,6 +24,8 @@
 #define RNG_BACKEND_CLASS(klass) \
     OBJECT_CLASS_CHECK(RngBackendClass, (klass), TYPE_RNG_BACKEND)
 
+#define TYPE_RNG_BUILTIN "rng-builtin"
+
 typedef struct RngRequest RngRequest;
 typedef struct RngBackendClass RngBackendClass;
 typedef struct RngBackend RngBackend;
diff --git a/qemu-options.hx b/qemu-options.hx
index d5233e189ceb..cd1c68d8dc9a 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4325,7 +4325,7 @@ The @option{share} boolean option is @var{on} by default with memfd.
 Creates a random number generator backend which obtains entropy from
 QEMU builtin functions. The @option{id} parameter is a unique ID that
 will be used to reference this entropy backend from the @option{virtio-rng}
-device.
+device. By default, the @option{virtio-rng} device uses this RNG backend.
 
 @item -object rng-random,id=@var{id},filename=@var{/dev/random}
 
-- 
2.20.1

Re: [Qemu-devel] [PATCH v6 2/4] rng-builtin: add an RNG backend that uses qemu_guest_getrandom()

[Daniel P. Berrangé]

On Tue, May 21, 2019 at 04:11:31PM +0200, Laurent Vivier wrote:
> Add a new RNG backend using QEMU builtin getrandom function.
> 
> It can be created and used with something like:
> 
>     ... -object rng-builtin,id=rng0 -device virtio-rng,rng=rng0 ...
> 
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  backends/Makefile.objs |  2 +-
>  backends/rng-builtin.c | 54 ++++++++++++++++++++++++++++++++++++++++++
>  qemu-options.hx        |  7 ++++++
>  3 files changed, 62 insertions(+), 1 deletion(-)
>  create mode 100644 backends/rng-builtin.c

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

Re: [Qemu-devel] [PATCH v6 1/4] VirtIO-RNG: Update default entropy source to `/dev/urandom`

[Ed Maste]

On Tue, 21 May 2019 at 10:15, Laurent Vivier <lvivier@redhat.com> wrote:
>
> From: Kashyap Chamarthy <kchamart@redhat.com>
>
> [...]
>
> Given the above, change the entropy source for VirtIO-RNG device to
> `/dev/urandom`.
>
> Related discussion in these[1][2] past threads.
>
> [1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html
>     -- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?"
> [2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html
>     -- "[RFC] Virtio RNG: Consider changing the default entropy source to
>        /dev/urandom"
>
> Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Acked-by: Ed Maste <emaste@freebsd.org>

Re: [Qemu-devel] [PATCH v6 0/4] rng-builtin: add an RNG backend that uses qemu_guest_getrandom()

[Laurent Vivier]

Michael,

the series seems ready to be merged, and the one from Richard is now 
part of master. Could you add it to one of your future virtio pull requests?

Thanks,
Laurent

On 21/05/2019 16:11, Laurent Vivier wrote:
> Add a new RNG backend using QEMU builtin getrandom function.
> 
> This patch applies on top of
>      "[PATCH v8 00/24] Add qemu_getrandom and ARMv8.5-RNG etc"
> Based-on: 20190517023924.1686-1-richard.henderson@linaro.org
> 
> v6: remove "sysemu/rng-random.h" from virtio-rng.c
>      rebase on qemu_getrandom v8
> 
> v5: PATCH 1 s/linux/Linux/
>      remove superfluous includes from rng-builtin.c
>      don't update rng-random documentation
>      add a patch from Markus to keep the default backend out of VirtIORNGConf
>      move TYPE_RNG_BUILTIN to sysemu/rng.h and remove sysemu/rng-builtin.h
> 
> v4: update PATCH 1 commit message
> 
> v3: Include Kashyap's patch in the series
>      Add a patch to change virtio-rng default backend to rng-builtin
> 
> v2: Update qemu-options.hx
>      describe the new backend and specify virtio-rng uses the
>      rng-random by default
> 
> Kashyap Chamarthy (1):
>    VirtIO-RNG: Update default entropy source to `/dev/urandom`
> 
> Laurent Vivier (2):
>    rng-builtin: add an RNG backend that uses qemu_guest_getrandom()
>    virtio-rng: change default backend to rng-builtin
> 
> Markus Armbruster (1):
>    virtio-rng: Keep the default backend out of VirtIORNGConf
> 
>   backends/Makefile.objs         |  2 +-
>   backends/rng-builtin.c         | 53 ++++++++++++++++++++++++++++++++++
>   backends/rng-random.c          |  2 +-
>   hw/virtio/virtio-rng.c         | 19 +++++-------
>   include/hw/virtio/virtio-rng.h |  2 --
>   include/sysemu/rng.h           |  2 ++
>   qemu-options.hx                |  9 +++++-
>   7 files changed, 73 insertions(+), 16 deletions(-)
>   create mode 100644 backends/rng-builtin.c
>