Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750989AbaGGEik (ORCPT ); Mon, 7 Jul 2014 00:38:40 -0400 Received: from mail-oa0-f53.google.com ([209.85.219.53]:55125 "EHLO mail-oa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750758AbaGGEih (ORCPT ); Mon, 7 Jul 2014 00:38:37 -0400 MIME-Version: 1.0 In-Reply-To: References: Date: Sun, 6 Jul 2014 21:38:36 -0700 X-Google-Sender-Auth: 1lfi231t3yj0pjsGfRJMGaGQBnM Message-ID: Subject: Re: [PATCH v2 2/2] virtio: rng: ensure reads happen after successful probe From: Kees Cook To: Amit Shah Cc: LKML , Virtualization List , Rusty Russell , Herbert Xu , Jason Cooper , "# 3.4.x" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 4, 2014 at 10:34 PM, Amit Shah wrote: > The hwrng core asks for random data in the hwrng_register() call itself > from commit d9e7972619. This doesn't play well with virtio -- the > DRIVER_OK bit is only set by virtio core on a successful probe, and > we're not yet out of our probe routine when this call is made. This > causes the host to not acknowledge any requests we put in the virtqueue, > and the insmod or kernel boot process just waits for data to arrive from > the host, which never happens. Doesn't this mean that virtio-rng won't ever contribute entropy to the system? -Kees > > CC: Kees Cook > CC: Jason Cooper > CC: Herbert Xu > CC: # For v3.15+ > Signed-off-by: Amit Shah > --- > drivers/char/hw_random/core.c | 6 ++++++ > drivers/char/hw_random/virtio-rng.c | 10 ++++++++++ > 2 files changed, 16 insertions(+) > > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c > index df95e2f..50f5b76 100644 > --- a/drivers/char/hw_random/core.c > +++ b/drivers/char/hw_random/core.c > @@ -68,6 +68,12 @@ static void add_early_randomness(struct hwrng *rng) > unsigned char bytes[16]; > int bytes_read; > > + /* > + * Currently only virtio-rng cannot return data during device > + * probe, and that's handled in virtio-rng.c itself. If there > + * are more such devices, this call to rng_get_data can be > + * made conditional here instead of doing it per-device. > + */ > bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1); > if (bytes_read > 0) > add_device_randomness(bytes, bytes_read); > diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c > index f3e7150..157f27c 100644 > --- a/drivers/char/hw_random/virtio-rng.c > +++ b/drivers/char/hw_random/virtio-rng.c > @@ -38,6 +38,8 @@ struct virtrng_info { > int index; > }; > > +bool probe_done; > + > static void random_recv_done(struct virtqueue *vq) > { > struct virtrng_info *vi = vq->vdev->priv; > @@ -67,6 +69,13 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait) > int ret; > struct virtrng_info *vi = (struct virtrng_info *)rng->priv; > > + /* > + * Don't ask host for data till we're setup. This call can > + * happen during hwrng_register(), after commit d9e7972619. > + */ > + if (unlikely(!probe_done)) > + return 0; > + > if (!vi->busy) { > vi->busy = true; > init_completion(&vi->have_data); > @@ -137,6 +146,7 @@ static int probe_common(struct virtio_device *vdev) > return err; > } > > + probe_done = true; > return 0; > } > > -- > 1.9.3 > -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/