Re: [Qemu-devel] [PATCH 2/4] virtio-rng-pci: create a default backend if none exists

[Paolo Bonzini]

Il 26/10/2012 20:59, Paolo Bonzini ha scritto:
> Il 26/10/2012 19:21, Anthony Liguori ha scritto:
>> This allows you to specify:
>>
>>   $ qemu -device virtio-rng-pci
>>
>> And things will Just Work with a reasonable default.
>>
>> Signed-off-by: Anthony Liguori <address@hidden>
>> ---
>>  hw/virtio-pci.c | 13 +++++++++++++
>>  hw/virtio-rng.h |  2 ++
>>  2 files changed, 15 insertions(+)
>>
>> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
>> index 0dc2a06..cfdb779 100644
>> --- a/hw/virtio-pci.c
>> +++ b/hw/virtio-pci.c
>> @@ -885,6 +885,19 @@ static int virtio_rng_init_pci(PCIDevice *pci_dev)
>>      VirtIOPCIProxy *proxy = DO_UPCAST(VirtIOPCIProxy, pci_dev, pci_dev);
>>      VirtIODevice *vdev;
>>  
>> +    if (proxy->rng.rng == NULL) {
>> +        proxy->rng.default_backend = 
>> RNG_RANDOM(object_new(TYPE_RNG_RANDOM));
>> +
>> +        object_property_add_child(OBJECT(pci_dev),
>> +                                  "default-backend",
>> +                                  OBJECT(proxy->rng.default_backend),
>> +                                  NULL);
>> +
>> +        object_property_set_link(OBJECT(pci_dev),
>> +                                 OBJECT(proxy->rng.default_backend),
>> +                                 "rng", NULL);
>> +    }
>> +
>>      vdev = virtio_rng_init(&pci_dev->qdev, &proxy->rng);
>>      if (!vdev) {
>>          return -1;
>> diff --git a/hw/virtio-rng.h b/hw/virtio-rng.h
>> index fbb0104..63ddb96 100644
>> --- a/hw/virtio-rng.h
>> +++ b/hw/virtio-rng.h
>> @@ -13,12 +13,14 @@
>>  #define _QEMU_VIRTIO_RNG_H
>>  
>>  #include "qemu/rng.h"
>> +#include "qemu/rng-random.h"
>>  
>>  /* The Virtio ID for the virtio rng device */
>>  #define VIRTIO_ID_RNG    4
>>  
>>  struct VirtIORNGConf {
>>      RngBackend *rng;
>> +    RndRandom *default_backend;
>>  };
>>  
>>  #endif
>>
> 
> NACK.  Starting a guest that runs rngd (or just a malicious guest) will
> completely deprive the host of entropy.
> 
> If you make the default /dev/hwrng, however, that would be ok.

Also, does this break non-Linux?  What if the default was changed to
/dev/hwrng but an older Linux distro didn't have the device file at all?

Paolo