net: Fix for_each_netdev_feature on Big endian

The features attribute is of type u64 and stored in the native endianes on
the system. The for_each_set_bit() macro takes a pointer to a 32 bit array
and goes over the bits in this area. On little Endian systems this also
works with an u64 as the most significant bit is on the highest address,
but on big endian the words are swapped. When we expect bit 15 here we get
bit 47 (15 + 32).

This patch converts it more or less to its own for_each_set_bit()
implementation which works on 64 bit integers directly. This is then
completely in host endianness and should work like expected.

Fixes: fd867d51 ("net/core: generic support for disabling netdev features down stack")
Signed-off-by: Hauke Mehrtens <hauke.mehrtens@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdev_features.h

@@ -11,6 +11,7 @@
 #define _LINUX_NETDEV_FEATURES_H
 
 #include <linux/types.h>
+#include <asm/byteorder.h>
 
 typedef u64 netdev_features_t;
 
@@ -154,8 +155,26 @@ enum {
 #define NETIF_F_HW_TLS_TX	__NETIF_F(HW_TLS_TX)
 #define NETIF_F_HW_TLS_RX	__NETIF_F(HW_TLS_RX)
 
+/* Finds the next feature with the highest number of the range of start till 0.
+ */
+static inline int find_next_netdev_feature(u64 feature, unsigned long start)
+{
+	/* like BITMAP_LAST_WORD_MASK() for u64
+	 * this sets the most significant 64 - start to 0.
+	 */
+	feature &= ~0ULL >> (-start & ((sizeof(feature) * 8) - 1));
+
+	return fls64(feature) - 1;
+}
+
+/* This goes for the MSB to the LSB through the set feature bits,
+ * mask_addr should be a u64 and bit an int
+ */
 #define for_each_netdev_feature(mask_addr, bit)				\
-	for_each_set_bit(bit, (unsigned long *)mask_addr, NETDEV_FEATURE_COUNT)
+	for ((bit) = find_next_netdev_feature((mask_addr),		\
+					      NETDEV_FEATURE_COUNT);	\
+	     (bit) >= 0;						\
+	     (bit) = find_next_netdev_feature((mask_addr), (bit) - 1))
 
 /* Features valid for ethtool to change */
 /* = all defined minus driver/device-class-related */

net/core/dev.c

@@ -8152,7 +8152,7 @@ static netdev_features_t netdev_sync_upper_features(struct net_device *lower,
 	netdev_features_t feature;
 	int feature_bit;
 
-	for_each_netdev_feature(&upper_disables, feature_bit) {
+	for_each_netdev_feature(upper_disables, feature_bit) {
 		feature = __NETIF_F_BIT(feature_bit);
 		if (!(upper->wanted_features & feature)
 		    && (features & feature)) {
@@ -8172,7 +8172,7 @@ static void netdev_sync_lower_features(struct net_device *upper,
 	netdev_features_t feature;
 	int feature_bit;
 
-	for_each_netdev_feature(&upper_disables, feature_bit) {
+	for_each_netdev_feature(upper_disables, feature_bit) {
 		feature = __NETIF_F_BIT(feature_bit);
 		if (!(features & feature) && (lower->features & feature)) {
 			netdev_dbg(upper, "Disabling feature %pNF on lower dev %s.\n",