dpaa_eth: reserve space for the xdp_frame under the A050385 erratum

When the erratum workaround is triggered, the newly created xdp_frame
structure is stored at the start of the newly allocated buffer. Avoid
the structure from being overwritten by explicitly reserving enough
space in the buffer for storing it.

Account for the fact that the structure's size might increase in time by
aligning the headroom to DPAA_FD_DATA_ALIGNMENT bytes, thus guaranteeing
the data's alignment.

Fixes: ae680bcb ("dpaa_eth: implement the A050385 erratum workaround for XDP")
Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Acked-by: Madalin Bucur <madalin.bucur@oss.nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/dpaa/dpaa_eth.c

@@ -2182,6 +2182,7 @@ static int dpaa_a050385_wa_xdpf(struct dpaa_priv *priv,
 	struct xdp_frame *new_xdpf, *xdpf = *init_xdpf;
 	void *new_buff;
 	struct page *p;
+	int headroom;
 
 	/* Check the data alignment and make sure the headroom is large
 	 * enough to store the xdpf backpointer. Use an aligned headroom
@@ -2197,19 +2198,34 @@ static int dpaa_a050385_wa_xdpf(struct dpaa_priv *priv,
 		return 0;
 	}
 
+	/* The new xdp_frame is stored in the new buffer. Reserve enough space
+	 * in the headroom for storing it along with the driver's private
+	 * info. The headroom needs to be aligned to DPAA_FD_DATA_ALIGNMENT to
+	 * guarantee the data's alignment in the buffer.
+	 */
+	headroom = ALIGN(sizeof(*new_xdpf) + priv->tx_headroom,
+			 DPAA_FD_DATA_ALIGNMENT);
+
+	/* Assure the extended headroom and data don't overflow the buffer,
+	 * while maintaining the mandatory tailroom.
+	 */
+	if (headroom + xdpf->len > DPAA_BP_RAW_SIZE -
+			SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
+		return -ENOMEM;
+
 	p = dev_alloc_pages(0);
 	if (unlikely(!p))
 		return -ENOMEM;
 
 	/* Copy the data to the new buffer at a properly aligned offset */
 	new_buff = page_address(p);
-	memcpy(new_buff + priv->tx_headroom, xdpf->data, xdpf->len);
+	memcpy(new_buff + headroom, xdpf->data, xdpf->len);
 
 	/* Create an XDP frame around the new buffer in a similar fashion
 	 * to xdp_convert_buff_to_frame.
 	 */
 	new_xdpf = new_buff;
-	new_xdpf->data = new_buff + priv->tx_headroom;
+	new_xdpf->data = new_buff + headroom;
 	new_xdpf->len = xdpf->len;
 	new_xdpf->headroom = priv->tx_headroom;
 	new_xdpf->frame_sz = DPAA_BP_RAW_SIZE;