[PATCH] virtio_console: fix sparse warnings

[PATCH] virtio_console: fix sparse warnings

[Michael S. Tsirkin]

CHECK drivers/char/virtio_console.c
drivers/char/virtio_console.c:687:36: warning: incorrect type in
	argument 1 (different address spaces)
drivers/char/virtio_console.c:687:36:    expected void [noderef]
	<asn:1>*to
drivers/char/virtio_console.c:687:36:    got char *out_buf
drivers/char/virtio_console.c:790:35: warning: incorrect type in
	argument 2 (different address spaces)
drivers/char/virtio_console.c:790:35:    expected char *out_buf
drivers/char/virtio_console.c:790:35:    got char [noderef]
	<asn:1>*ubuf

fill_readbuf is reused with both kernel and userspace pointers,
depending on value of to_user flag.

Tag address parameter as __user, and cast to/from regular pointer type
when we know it's safe.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/char/virtio_console.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 775c898..ccb5357 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -669,8 +669,8 @@ done:
  * 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,
-			    bool to_user)
+static ssize_t fill_readbuf(struct port *port, char __user *out_buf,
+			    size_t out_count, bool to_user)
 {
 	struct port_buffer *buf;
 	unsigned long flags;
@@ -688,7 +688,8 @@ static ssize_t fill_readbuf(struct port *port, char *out_buf, size_t out_count,
 		if (ret)
 			return -EFAULT;
 	} else {
-		memcpy(out_buf, buf->buf + buf->offset, out_count);
+		memcpy((__force char *)out_buf, buf->buf + buf->offset,
+		       out_count);
 	}
 
 	buf->offset += out_count;
@@ -1162,7 +1163,7 @@ 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, false);
+	return fill_readbuf(port, (__force char __user *)buf, count, false);
 }
 
 static void resize_console(struct port *port)
-- 
MST

Re: [PATCH] virtio_console: fix sparse warnings

[Greg Kroah-Hartman]

On Mon, Dec 01, 2014 at 01:35:57PM +0200, Michael S. Tsirkin wrote:
> CHECK drivers/char/virtio_console.c
> drivers/char/virtio_console.c:687:36: warning: incorrect type in
> 	argument 1 (different address spaces)
> drivers/char/virtio_console.c:687:36:    expected void [noderef]
> 	<asn:1>*to
> drivers/char/virtio_console.c:687:36:    got char *out_buf
> drivers/char/virtio_console.c:790:35: warning: incorrect type in
> 	argument 2 (different address spaces)
> drivers/char/virtio_console.c:790:35:    expected char *out_buf
> drivers/char/virtio_console.c:790:35:    got char [noderef]
> 	<asn:1>*ubuf
> 
> fill_readbuf is reused with both kernel and userspace pointers,
> depending on value of to_user flag.

That's horrid, don't do that.  Have two different functions for this
type of thing, otherwise you defeat the whole purpose of trying to track
__user pointers.

thanks,

greg k-h