hwrng: virtio - ensure reads happen after successful probe

commit e052dbf554610e2104c5a7518c4d8374bed701bb upstream.

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 <keescook@chromium.org>
CC: Jason Cooper <jason@lakedaemon.net>
CC: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 2a451b14b3cc687659cff283aa283361c3d92094..c4419ea1ab078485f629ea6853b854dd6621aeb3 100644 (file)
--- 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 2ce0e225e58c3edbceeafa290c8db065eb4e6e72..e4ecf99971fe36f7e28dfd022a011bc02e5a9e18 100644 (file)
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -30,6 +30,8 @@ static unsigned int data_avail;
 static DECLARE_COMPLETION(have_data);
 static bool busy;
 
+static bool probe_done;
+
 static void random_recv_done(struct virtqueue *vq)
 {
        /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
@@ -56,6 +58,13 @@ static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
 {
        int ret;
 
+       /*
+        * 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 (!busy) {
                busy = true;
                init_completion(&have_data);
@@ -110,6 +119,7 @@ static int probe_common(struct virtio_device *vdev)
                return err;
        }
 
+       probe_done = true;
        return 0;
 }