According to the virtio v1.x "entropy device" specification, a virtio-rng
device is supposed to always return at least one byte of entropy.
However the virtio v0.9 spec does not mention such a requirement.
The Arm Fixed Virtual Platform (FVP) implementation of virtio-rng always
returns 8 bytes less of entropy than requested. If 8 bytes or less are
requested, it will return 0 bytes.
This behaviour makes U-Boot's virtio_rng_read() implementation go into an
endless loop, hanging the system.
Work around this problem by always requesting 8 bytes more than needed,
but only if a previous call to virtqueue_get_buf() returned 0 bytes.
This should never trigger on a v1.x spec compliant implementation, but
fixes the hang on the Arm FVP.
Signed-off-by: Andre Przywara <andre.przyw...@arm.com>
Reported-by: Peter Hoyes <peter.ho...@arm.com>
---
drivers/virtio/virtio_rng.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_rng.c b/drivers/virtio/virtio_rng.c
index b85545c2ee5..786359a6e36 100644
--- a/drivers/virtio/virtio_rng.c
+++ b/drivers/virtio/virtio_rng.c
@@ -20,7 +20,7 @@ struct virtio_rng_priv {
static int virtio_rng_read(struct udevice *dev, void *data, size_t len)
{
int ret;
- unsigned int rsize;
+ unsigned int rsize = 1;
unsigned char buf[BUFFER_SIZE] __aligned(4);
unsigned char *ptr = data;
struct virtio_sg sg;
@@ -29,7 +29,12 @@ static int virtio_rng_read(struct udevice *dev, void *data,
size_t len)
while (len) {
sg.addr = buf;
- sg.length = min(len, sizeof(buf));
+ /*
+ * Work around implementations which always return 8 bytes
+ * less than requested, down to 0 bytes, which would
+ * cause an endless loop otherwise.
+ */
+ sg.length = min(rsize ? len : len + 8, sizeof(buf));
sgs[0] = &sg;
ret = virtqueue_add(priv->rng_vq, sgs, 0, 1);
--
2.25.1
