From 3cae45f6c0c1bd54aec08d14ab4d9272b1f433e5 Mon Sep 17 00:00:00 2001
From: Doug Berger <opendmb@gmail.com>
Date: Wed, 24 Jun 2020 18:14:55 -0700
Subject: [PATCH 1/4] net: bcmgenet: use hardware padding of runt frames
Patch-mainline: v5.8-rc3
Git-commit: 20d1f2d1b024f6be199a3bedf1578a1d21592bc5
References: git-fixes

When commit 474ea9cafc45 ("net: bcmgenet: correctly pad short
packets") added the call to skb_padto() it should have been
located before the nr_frags parameter was read since that value
could be changed when padding packets with lengths between 55
and 59 bytes (inclusive).

The use of a stale nr_frags value can cause corruption of the
pad data when tx-scatter-gather is enabled. This corruption of
the pad can cause invalid checksum computation when hardware
offload of tx-checksum is also enabled.

Since the original reason for the padding was corrected by
commit 7dd399130efb ("net: bcmgenet: fix skb_len in
bcmgenet_xmit_single()") we can remove the software padding all
together and make use of hardware padding of short frames as
long as the hardware also always appends the FCS value to the
frame.

Fixes: 474ea9cafc45 ("net: bcmgenet: correctly pad short packets")
Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
---
 drivers/net/ethernet/broadcom/genet/bcmgenet.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index db7c89c28fb0..18a0da74089d 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -2057,11 +2057,6 @@ static netdev_tx_t bcmgenet_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto out;
 	}
 
-	if (skb_padto(skb, ETH_ZLEN)) {
-		ret = NETDEV_TX_OK;
-		goto out;
-	}
-
 	/* Retain how many bytes will be sent on the wire, without TSB inserted
 	 * by transmit checksum offload
 	 */
@@ -2110,6 +2105,9 @@ static netdev_tx_t bcmgenet_xmit(struct sk_buff *skb, struct net_device *dev)
 		len_stat = (size << DMA_BUFLENGTH_SHIFT) |
 			   (priv->hw_params->qtag_mask << DMA_TX_QTAG_SHIFT);
 
+		/* Note: if we ever change from DMA_TX_APPEND_CRC below we
+		 * will need to restore software padding of "runt" packets
+		 */
 		if (!i) {
 			len_stat |= DMA_TX_APPEND_CRC | DMA_SOP;
 			if (skb->ip_summed == CHECKSUM_PARTIAL)
-- 
2.16.4