From e052dbf554610e2104c5a7518c4d8374bed701bb Mon Sep 17 00:00:00 2001 From: Amit Shah Date: Thu, 10 Jul 2014 15:42:35 +0530 Subject: [PATCH] hwrng: virtio - ensure reads happen after successful probe 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. CC: Kees Cook CC: Jason Cooper CC: Herbert Xu CC: # For v3.15+ Reviewed-by: Jason Cooper Signed-off-by: Amit Shah Signed-off-by: Herbert Xu --- 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 2a451b14b3cc..c4419ea1ab07 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 f3e71501de54..e9b15bc18b4d 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; }; +static 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; } -- 2.20.1