virtio: console: Prepare for writing to userspace buffers

When ports get advertised as char devices, the buffers will come from
userspace. Equip the fill_readbuf function with the ability to write
to userspace buffers.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 14 insertions, 6 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index a70f2b3a9e64..8e447e1e12bc 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -358,7 +358,8 @@ fail:
  * Give out the data that's requested from the buffer that we have
  * queued up.
  */
-static ssize_t fill_readbuf(struct port *port, char *out_buf, size_t out_count)
+static ssize_t fill_readbuf(struct port *port, char *out_buf, size_t out_count,
+                            bool to_user)
 {
         struct port_buffer *buf;
         unsigned long flags;
@@ -367,12 +368,18 @@ static ssize_t fill_readbuf(struct port *port, char *out_buf, size_t out_count)
                 return 0;
 
         buf = port->inbuf;
-        if (out_count > buf->len - buf->offset)
-                out_count = buf->len - buf->offset;
+        out_count = min(out_count, buf->len - buf->offset);
 
-        memcpy(out_buf, buf->buf + buf->offset, out_count);
+        if (to_user) {
+                ssize_t ret;
+
+                ret = copy_to_user(out_buf, buf->buf + buf->offset, out_count);
+                if (ret)
+                        return -EFAULT;
+        } else {
+                memcpy(out_buf, buf->buf + buf->offset, out_count);
+        }
 
-        /* Return the number of bytes actually copied */
         buf->offset += out_count;
 
         if (buf->offset == buf->len) {
@@ -388,6 +395,7 @@ static ssize_t fill_readbuf(struct port *port, char *out_buf, size_t out_count)
 
                 spin_unlock_irqrestore(&port->inbuf_lock, flags);
         }
+        /* Return the number of bytes actually copied */
         return out_count;
 }
 
@@ -431,7 +439,7 @@ static int get_chars(u32 vtermno, char *buf, int count)
         /* If we don't have an input queue yet, we can't get input. */
         BUG_ON(!port->in_vq);
 
-        return fill_readbuf(port, buf, count);
+        return fill_readbuf(port, buf, count, false);
 }
 
 static void resize_console(struct port *port)