18 files changed, 435 insertions, 12 deletions

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
index 1389ab5e05df..1f0e872d0667 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
@@ -113,10 +113,10 @@ bool bnxt_rx_xdp(struct bnxt *bp, struct bnxt_rx_ring_info *rxr, u16 cons,
 	if (tx_avail != bp->tx_ring_size)
 		*event &= ~BNXT_RX_EVENT;
 
+	*len = xdp.data_end - xdp.data;
 	if (orig_data != xdp.data) {
 		offset = xdp.data - xdp.data_hard_start;
 		*data_ptr = xdp.data_hard_start + offset;
-		*len = xdp.data_end - xdp.data;
 	}
 	switch (act) {
 	case XDP_PASS:
diff --git a/drivers/net/ethernet/cavium/thunder/nicvf_main.c b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
index 707db3304396..7135db45927e 100644
--- a/drivers/net/ethernet/cavium/thunder/nicvf_main.c
+++ b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
@@ -538,9 +538,9 @@ static inline bool nicvf_xdp_rx(struct nicvf *nic, struct bpf_prog *prog,
 	action = bpf_prog_run_xdp(prog, &xdp);
 	rcu_read_unlock();
 
+	len = xdp.data_end - xdp.data;
 	/* Check if XDP program has changed headers */
 	if (orig_data != xdp.data) {
-		len = xdp.data_end - xdp.data;
 		offset = orig_data - xdp.data;
 		dma_addr -= offset;
 	}
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
index 5c613c6663da..efc55feddc5c 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
@@ -775,8 +775,8 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
 
 			act = bpf_prog_run_xdp(xdp_prog, &xdp);
 
+			length = xdp.data_end - xdp.data;
 			if (xdp.data != orig_data) {
-				length = xdp.data_end - xdp.data;
 				frags[0].page_offset = xdp.data -
 					xdp.data_hard_start;
 				va = xdp.data;
diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
index 1eb6549f2a54..d9111c077699 100644
--- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
+++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
@@ -1722,7 +1722,7 @@ static int nfp_net_rx(struct nfp_net_rx_ring *rx_ring, int budget)
 
 			act = bpf_prog_run_xdp(xdp_prog, &xdp);
 
-			pkt_len -= xdp.data - orig_data;
+			pkt_len = xdp.data_end - xdp.data;
 			pkt_off += xdp.data - orig_data;
 
 			switch (act) {
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1e58be152d5c..901351a6ed21 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1696,6 +1696,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 			return NULL;
 		case XDP_PASS:
 			delta = orig_data - xdp.data;
+			len = xdp.data_end - xdp.data;
 			break;
 		default:
 			bpf_warn_invalid_xdp_action(act);
@@ -1716,7 +1717,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	}
 
 	skb_reserve(skb, pad - delta);
-	skb_put(skb, len + delta);
+	skb_put(skb, len);
 	get_page(alloc_frag->page);
 	alloc_frag->offset += buflen;
 
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 01694e26f03e..779a4f798522 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -606,6 +606,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
 		case XDP_PASS:
 			/* Recalculate length in case bpf program changed it */
 			delta = orig_data - xdp.data;
+			len = xdp.data_end - xdp.data;
 			break;
 		case XDP_TX:
 			xdpf = convert_to_xdp_frame(&xdp);
@@ -642,7 +643,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
 		goto err;
 	}
 	skb_reserve(skb, headroom - delta);
-	skb_put(skb, len + delta);
+	skb_put(skb, len);
 	if (!delta) {
 		buf += header_offset;
 		memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
@@ -757,6 +758,10 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 			offset = xdp.data -
 					page_address(xdp_page) - vi->hdr_len;
 
+			/* recalculate len if xdp.data or xdp.data_end were
+			 * adjusted
+			 */
+			len = xdp.data_end - xdp.data;
 			/* We can only create skb based on xdp_page. */
 			if (unlikely(xdp_page != page)) {
 				rcu_read_unlock();
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c5ec89732a8d..9a2d1a04eb24 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -755,6 +755,13 @@ union bpf_attr {
  *     @addr: pointer to struct sockaddr to bind socket to
  *     @addr_len: length of sockaddr structure
  *     Return: 0 on success or negative error code
+ *
+ * int bpf_xdp_adjust_tail(xdp_md, delta)
+ *     Adjust the xdp_md.data_end by delta. Only shrinking of packet's
+ *     size is supported.
+ *     @xdp_md: pointer to xdp_md
+ *     @delta: A negative integer to be added to xdp_md.data_end
+ *     Return: 0 on success or negative on error
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -821,7 +828,8 @@ union bpf_attr {
 	FN(msg_apply_bytes),		\
 	FN(msg_cork_bytes),		\
 	FN(msg_pull_data),		\
-	FN(bind),
+	FN(bind),			\
+	FN(xdp_adjust_tail),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 2ced48662c1f..68c3578343b4 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -170,7 +170,8 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 	xdp.rxq = &rxqueue->xdp_rxq;
 
 	retval = bpf_test_run(prog, &xdp, repeat, &duration);
-	if (xdp.data != data + XDP_PACKET_HEADROOM + NET_IP_ALIGN)
+	if (xdp.data != data + XDP_PACKET_HEADROOM + NET_IP_ALIGN ||
+	    xdp.data_end != xdp.data + size)
 		size = xdp.data_end - xdp.data;
 	ret = bpf_test_finish(kattr, uattr, xdp.data, size, retval, duration);
 	kfree(data);
diff --git a/net/core/dev.c b/net/core/dev.c
index 969462ebb296..11c789231a03 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3996,9 +3996,9 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
 				     struct bpf_prog *xdp_prog)
 {
 	struct netdev_rx_queue *rxqueue;
+	void *orig_data, *orig_data_end;
 	u32 metalen, act = XDP_DROP;
 	struct xdp_buff xdp;
-	void *orig_data;
 	int hlen, off;
 	u32 mac_len;
 
@@ -4037,6 +4037,7 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
 	xdp.data_meta = xdp.data;
 	xdp.data_end = xdp.data + hlen;
 	xdp.data_hard_start = skb->data - skb_headroom(skb);
+	orig_data_end = xdp.data_end;
 	orig_data = xdp.data;
 
 	rxqueue = netif_get_rxqueue(skb);
@@ -4051,6 +4052,13 @@ static u32 netif_receive_generic_xdp(struct sk_buff *skb,
 		__skb_push(skb, -off);
 	skb->mac_header += off;
 
+	/* check if bpf_xdp_adjust_tail was used. it can only "shrink"
+	 * pckt.
+	 */
+	off = orig_data_end - xdp.data_end;
+	if (off != 0)
+		skb_set_tail_pointer(skb, xdp.data_end - xdp.data);
+
 	switch (act) {
 	case XDP_REDIRECT:
 	case XDP_TX:
diff --git a/net/core/filter.c b/net/core/filter.c
index a374b8560bc4..29318598fd60 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2725,6 +2725,30 @@ static const struct bpf_func_proto bpf_xdp_adjust_head_proto = {
 	.arg2_type	= ARG_ANYTHING,
 };
 
+BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
+{
+	void *data_end = xdp->data_end + offset;
+
+	/* only shrinking is allowed for now. */
+	if (unlikely(offset >= 0))
+		return -EINVAL;
+
+	if (unlikely(data_end < xdp->data + ETH_HLEN))
+		return -EINVAL;
+
+	xdp->data_end = data_end;
+
+	return 0;
+}
+
+static const struct bpf_func_proto bpf_xdp_adjust_tail_proto = {
+	.func		= bpf_xdp_adjust_tail,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_ANYTHING,
+};
+
 BPF_CALL_2(bpf_xdp_adjust_meta, struct xdp_buff *, xdp, int, offset)
 {
 	void *meta = xdp->data_meta + offset;
@@ -3074,7 +3098,8 @@ bool bpf_helper_changes_pkt_data(void *func)
 	    func == bpf_l4_csum_replace ||
 	    func == bpf_xdp_adjust_head ||
 	    func == bpf_xdp_adjust_meta ||
-	    func == bpf_msg_pull_data)
+	    func == bpf_msg_pull_data ||
+	    func == bpf_xdp_adjust_tail)
 		return true;
 
 	return false;
@@ -3888,6 +3913,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_xdp_redirect_proto;
 	case BPF_FUNC_redirect_map:
 		return &bpf_xdp_redirect_map_proto;
+	case BPF_FUNC_xdp_adjust_tail:
+		return &bpf_xdp_adjust_tail_proto;
 	default:
 		return bpf_base_func_proto(func_id);
 	}
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 4d6a6edd4bf6..aa8c392e2e52 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -44,6 +44,7 @@ hostprogs-y += xdp_monitor
 hostprogs-y += xdp_rxq_info
 hostprogs-y += syscall_tp
 hostprogs-y += cpustat
+hostprogs-y += xdp_adjust_tail
 
 # Libbpf dependencies
 LIBBPF := ../../tools/lib/bpf/bpf.o ../../tools/lib/bpf/nlattr.o
@@ -95,6 +96,7 @@ xdp_monitor-objs := bpf_load.o $(LIBBPF) xdp_monitor_user.o
 xdp_rxq_info-objs := bpf_load.o $(LIBBPF) xdp_rxq_info_user.o
 syscall_tp-objs := bpf_load.o $(LIBBPF) syscall_tp_user.o
 cpustat-objs := bpf_load.o $(LIBBPF) cpustat_user.o
+xdp_adjust_tail-objs := bpf_load.o $(LIBBPF) xdp_adjust_tail_user.o
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
@@ -148,6 +150,7 @@ always += xdp_rxq_info_kern.o
 always += xdp2skb_meta_kern.o
 always += syscall_tp_kern.o
 always += cpustat_kern.o
+always += xdp_adjust_tail_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
 HOSTCFLAGS += -I$(srctree)/tools/lib/
@@ -193,6 +196,7 @@ HOSTLOADLIBES_xdp_monitor += -lelf
 HOSTLOADLIBES_xdp_rxq_info += -lelf
 HOSTLOADLIBES_syscall_tp += -lelf
 HOSTLOADLIBES_cpustat += -lelf
+HOSTLOADLIBES_xdp_adjust_tail += -lelf
 
 # Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
 #  make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
diff --git a/samples/bpf/xdp_adjust_tail_kern.c b/samples/bpf/xdp_adjust_tail_kern.c
new file mode 100644
index 000000000000..411fdb21f8bc
--- /dev/null
+++ b/samples/bpf/xdp_adjust_tail_kern.c
@@ -0,0 +1,152 @@
+/* SPDX-License-Identifier: GPL-2.0
+ * Copyright (c) 2018 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program shows how to use bpf_xdp_adjust_tail() by
+ * generating ICMPv4 "packet to big" (unreachable/ df bit set frag needed
+ * to be more preice in case of v4)" where receiving packets bigger then
+ * 600 bytes.
+ */
+#define KBUILD_MODNAME "foo"
+#include <uapi/linux/bpf.h>
+#include <linux/in.h>
+#include <linux/if_ether.h>
+#include <linux/if_packet.h>
+#include <linux/if_vlan.h>
+#include <linux/ip.h>
+#include <linux/icmp.h>
+#include "bpf_helpers.h"
+
+#define DEFAULT_TTL 64
+#define MAX_PCKT_SIZE 600
+#define ICMP_TOOBIG_SIZE 98
+#define ICMP_TOOBIG_PAYLOAD_SIZE 92
+
+struct bpf_map_def SEC("maps") icmpcnt = {
+	.type = BPF_MAP_TYPE_ARRAY,
+	.key_size = sizeof(__u32),
+	.value_size = sizeof(__u64),
+	.max_entries = 1,
+};
+
+static __always_inline void count_icmp(void)
+{
+	u64 key = 0;
+	u64 *icmp_count;
+
+	icmp_count = bpf_map_lookup_elem(&icmpcnt, &key);
+	if (icmp_count)
+		*icmp_count += 1;
+}
+
+static __always_inline void swap_mac(void *data, struct ethhdr *orig_eth)
+{
+	struct ethhdr *eth;
+
+	eth = data;
+	memcpy(eth->h_source, orig_eth->h_dest, ETH_ALEN);
+	memcpy(eth->h_dest, orig_eth->h_source, ETH_ALEN);
+	eth->h_proto = orig_eth->h_proto;
+}
+
+static __always_inline __u16 csum_fold_helper(__u32 csum)
+{
+	return ~((csum & 0xffff) + (csum >> 16));
+}
+
+static __always_inline void ipv4_csum(void *data_start, int data_size,
+				      __u32 *csum)
+{
+	*csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
+	*csum = csum_fold_helper(*csum);
+}
+
+static __always_inline int send_icmp4_too_big(struct xdp_md *xdp)
+{
+	int headroom = (int)sizeof(struct iphdr) + (int)sizeof(struct icmphdr);
+
+	if (bpf_xdp_adjust_head(xdp, 0 - headroom))
+		return XDP_DROP;
+	void *data = (void *)(long)xdp->data;
+	void *data_end = (void *)(long)xdp->data_end;
+
+	if (data + (ICMP_TOOBIG_SIZE + headroom) > data_end)
+		return XDP_DROP;
+
+	struct iphdr *iph, *orig_iph;
+	struct icmphdr *icmp_hdr;
+	struct ethhdr *orig_eth;
+	__u32 csum = 0;
+	__u64 off = 0;
+
+	orig_eth = data + headroom;
+	swap_mac(data, orig_eth);
+	off += sizeof(struct ethhdr);
+	iph = data + off;
+	off += sizeof(struct iphdr);
+	icmp_hdr = data + off;
+	off += sizeof(struct icmphdr);
+	orig_iph = data + off;
+	icmp_hdr->type = ICMP_DEST_UNREACH;
+	icmp_hdr->code = ICMP_FRAG_NEEDED;
+	icmp_hdr->un.frag.mtu = htons(MAX_PCKT_SIZE-sizeof(struct ethhdr));
+	icmp_hdr->checksum = 0;
+	ipv4_csum(icmp_hdr, ICMP_TOOBIG_PAYLOAD_SIZE, &csum);
+	icmp_hdr->checksum = csum;
+	iph->ttl = DEFAULT_TTL;
+	iph->daddr = orig_iph->saddr;
+	iph->saddr = orig_iph->daddr;
+	iph->version = 4;
+	iph->ihl = 5;
+	iph->protocol = IPPROTO_ICMP;
+	iph->tos = 0;
+	iph->tot_len = htons(
+		ICMP_TOOBIG_SIZE + headroom - sizeof(struct ethhdr));
+	iph->check = 0;
+	csum = 0;
+	ipv4_csum(iph, sizeof(struct iphdr), &csum);
+	iph->check = csum;
+	count_icmp();
+	return XDP_TX;
+}
+
+
+static __always_inline int handle_ipv4(struct xdp_md *xdp)
+{
+	void *data_end = (void *)(long)xdp->data_end;
+	void *data = (void *)(long)xdp->data;
+	int pckt_size = data_end - data;
+	int offset;
+
+	if (pckt_size > MAX_PCKT_SIZE) {
+		offset = pckt_size - ICMP_TOOBIG_SIZE;
+		if (bpf_xdp_adjust_tail(xdp, 0 - offset))
+			return XDP_PASS;
+		return send_icmp4_too_big(xdp);
+	}
+	return XDP_PASS;
+}
+
+SEC("xdp_icmp")
+int _xdp_icmp(struct xdp_md *xdp)
+{
+	void *data_end = (void *)(long)xdp->data_end;
+	void *data = (void *)(long)xdp->data;
+	struct ethhdr *eth = data;
+	__u16 h_proto;
+
+	if (eth + 1 > data_end)
+		return XDP_DROP;
+
+	h_proto = eth->h_proto;
+
+	if (h_proto == htons(ETH_P_IP))
+		return handle_ipv4(xdp);
+	else
+		return XDP_PASS;
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/samples/bpf/xdp_adjust_tail_user.c b/samples/bpf/xdp_adjust_tail_user.c
new file mode 100644
index 000000000000..f621a541b574
--- /dev/null
+++ b/samples/bpf/xdp_adjust_tail_user.c
@@ -0,0 +1,142 @@
+/* SPDX-License-Identifier: GPL-2.0
+ * Copyright (c) 2018 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <linux/bpf.h>
+#include <linux/if_link.h>
+#include <assert.h>
+#include <errno.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/resource.h>
+#include <arpa/inet.h>
+#include <netinet/ether.h>
+#include <unistd.h>
+#include <time.h>
+#include "bpf_load.h"
+#include "libbpf.h"
+#include "bpf_util.h"
+
+#define STATS_INTERVAL_S 2U
+
+static int ifindex = -1;
+static __u32 xdp_flags;
+
+static void int_exit(int sig)
+{
+	if (ifindex > -1)
+		bpf_set_link_xdp_fd(ifindex, -1, xdp_flags);
+	exit(0);
+}
+
+/* simple "icmp packet too big sent" counter
+ */
+static void poll_stats(unsigned int kill_after_s)
+{
+	time_t started_at = time(NULL);
+	__u64 value = 0;
+	int key = 0;
+
+
+	while (!kill_after_s || time(NULL) - started_at <= kill_after_s) {
+		sleep(STATS_INTERVAL_S);
+
+		assert(bpf_map_lookup_elem(map_fd[0], &key, &value) == 0);
+
+		printf("icmp \"packet too big\" sent: %10llu pkts\n", value);
+	}
+}
+
+static void usage(const char *cmd)
+{
+	printf("Start a XDP prog which send ICMP \"packet too big\" \n"
+		"messages if ingress packet is bigger then MAX_SIZE bytes\n");
+	printf("Usage: %s [...]\n", cmd);
+	printf("    -i <ifindex> Interface Index\n");
+	printf("    -T <stop-after-X-seconds> Default: 0 (forever)\n");
+	printf("    -S use skb-mode\n");
+	printf("    -N enforce native mode\n");
+	printf("    -h Display this help\n");
+}
+
+int main(int argc, char **argv)
+{
+	unsigned char opt_flags[256] = {};
+	unsigned int kill_after_s = 0;
+	const char *optstr = "i:T:SNh";
+	struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
+	char filename[256];
+	int opt;
+	int i;
+
+
+	for (i = 0; i < strlen(optstr); i++)
+		if (optstr[i] != 'h' && 'a' <= optstr[i] && optstr[i] <= 'z')
+			opt_flags[(unsigned char)optstr[i]] = 1;
+
+	while ((opt = getopt(argc, argv, optstr)) != -1) {
+
+		switch (opt) {
+		case 'i':
+			ifindex = atoi(optarg);
+			break;
+		case 'T':
+			kill_after_s = atoi(optarg);
+			break;
+		case 'S':
+			xdp_flags |= XDP_FLAGS_SKB_MODE;
+			break;
+		case 'N':
+			xdp_flags |= XDP_FLAGS_DRV_MODE;
+			break;
+		default:
+			usage(argv[0]);
+			return 1;
+		}
+		opt_flags[opt] = 0;
+	}
+
+	for (i = 0; i < strlen(optstr); i++) {
+		if (opt_flags[(unsigned int)optstr[i]]) {
+			fprintf(stderr, "Missing argument -%c\n", optstr[i]);
+			usage(argv[0]);
+			return 1;
+		}
+	}
+
+	if (setrlimit(RLIMIT_MEMLOCK, &r)) {
+		perror("setrlimit(RLIMIT_MEMLOCK, RLIM_INFINITY)");
+		return 1;
+	}
+
+	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+	if (load_bpf_file(filename)) {
+		printf("%s", bpf_log_buf);
+		return 1;
+	}
+
+	if (!prog_fd[0]) {
+		printf("load_bpf_file: %s\n", strerror(errno));
+		return 1;
+	}
+
+	signal(SIGINT, int_exit);
+	signal(SIGTERM, int_exit);
+
+	if (bpf_set_link_xdp_fd(ifindex, prog_fd[0], xdp_flags) < 0) {
+		printf("link set xdp fd failed\n");
+		return 1;
+	}
+
+	poll_stats(kill_after_s);
+
+	bpf_set_link_xdp_fd(ifindex, -1, xdp_flags);
+
+	return 0;
+}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 9d07465023a2..56bf493ba7ed 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -755,6 +755,13 @@ union bpf_attr {
  *     @addr: pointer to struct sockaddr to bind socket to
  *     @addr_len: length of sockaddr structure
  *     Return: 0 on success or negative error code
+ *
+ * int bpf_xdp_adjust_tail(xdp_md, delta)
+ *     Adjust the xdp_md.data_end by delta. Only shrinking of packet's
+ *     size is supported.
+ *     @xdp_md: pointer to xdp_md
+ *     @delta: A negative integer to be added to xdp_md.data_end
+ *     Return: 0 on success or negative on error
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -821,7 +828,8 @@ union bpf_attr {
 	FN(msg_apply_bytes),		\
 	FN(msg_cork_bytes),		\
 	FN(msg_pull_data),		\
-	FN(bind),
+	FN(bind),			\
+	FN(xdp_adjust_tail),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 0a315ddabbf4..3e819dc70bee 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -31,7 +31,7 @@ TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test
 	sockmap_verdict_prog.o dev_cgroup.o sample_ret0.o test_tracepoint.o \
 	test_l4lb_noinline.o test_xdp_noinline.o test_stacktrace_map.o \
 	sample_map_ret0.o test_tcpbpf_kern.o test_stacktrace_build_id.o \
-	sockmap_tcp_msg_prog.o connect4_prog.o connect6_prog.o
+	sockmap_tcp_msg_prog.o connect4_prog.o connect6_prog.o test_adjust_tail.o
 
 # Order correspond to 'make run_tests' order
 TEST_PROGS := test_kmod.sh \
diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
index d8223d99f96d..9271576bdc8f 100644
--- a/tools/testing/selftests/bpf/bpf_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_helpers.h
@@ -96,6 +96,9 @@ static int (*bpf_msg_pull_data)(void *ctx, int start, int end, int flags) =
 	(void *) BPF_FUNC_msg_pull_data;
 static int (*bpf_bind)(void *ctx, void *addr, int addr_len) =
 	(void *) BPF_FUNC_bind;
+static int (*bpf_xdp_adjust_tail)(void *ctx, int offset) =
+	(void *) BPF_FUNC_xdp_adjust_tail;
+
 
 /* llvm builtin functions that eBPF C program may use to
  * emit BPF_LD_ABS and BPF_LD_IND instructions
@@ -129,6 +132,8 @@ static int (*bpf_l3_csum_replace)(void *ctx, int off, int from, int to, int flag
 	(void *) BPF_FUNC_l3_csum_replace;
 static int (*bpf_l4_csum_replace)(void *ctx, int off, int from, int to, int flags) =
 	(void *) BPF_FUNC_l4_csum_replace;
+static int (*bpf_csum_diff)(void *from, int from_size, void *to, int to_size, int seed) =
+	(void *) BPF_FUNC_csum_diff;
 static int (*bpf_skb_under_cgroup)(void *ctx, void *map, int index) =
 	(void *) BPF_FUNC_skb_under_cgroup;
 static int (*bpf_skb_change_head)(void *, int len, int flags) =
diff --git a/tools/testing/selftests/bpf/test_adjust_tail.c b/tools/testing/selftests/bpf/test_adjust_tail.c
new file mode 100644
index 000000000000..4cd5e860c903
--- /dev/null
+++ b/tools/testing/selftests/bpf/test_adjust_tail.c
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0
+ * Copyright (c) 2018 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <linux/bpf.h>
+#include <linux/if_ether.h>
+#include "bpf_helpers.h"
+
+int _version SEC("version") = 1;
+
+SEC("xdp_adjust_tail")
+int _xdp_adjust_tail(struct xdp_md *xdp)
+{
+	void *data_end = (void *)(long)xdp->data_end;
+	void *data = (void *)(long)xdp->data;
+	int offset = 0;
+
+	if (data_end - data == 54)
+		offset = 256;
+	else
+		offset = 20;
+	if (bpf_xdp_adjust_tail(xdp, 0 - offset))
+		return XDP_DROP;
+	return XDP_TX;
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
index faadbe233966..eedda98d7bb1 100644
--- a/tools/testing/selftests/bpf/test_progs.c
+++ b/tools/testing/selftests/bpf/test_progs.c
@@ -166,6 +166,37 @@ out:
 	bpf_object__close(obj);
 }
 
+static void test_xdp_adjust_tail(void)
+{
+	const char *file = "./test_adjust_tail.o";
+	struct bpf_object *obj;
+	char buf[128];
+	__u32 duration, retval, size;
+	int err, prog_fd;
+
+	err = bpf_prog_load(file, BPF_PROG_TYPE_XDP, &obj, &prog_fd);
+	if (err) {
+		error_cnt++;
+		return;
+	}
+
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				buf, &size, &retval, &duration);
+
+	CHECK(err || errno || retval != XDP_DROP,
+	      "ipv4", "err %d errno %d retval %d size %d\n",
+	      err, errno, retval, size);
+
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v6, sizeof(pkt_v6),
+				buf, &size, &retval, &duration);
+	CHECK(err || errno || retval != XDP_TX || size != 54,
+	      "ipv6", "err %d errno %d retval %d size %d\n",
+	      err, errno, retval, size);
+	bpf_object__close(obj);
+}
+
+
+
 #define MAGIC_VAL 0x1234
 #define NUM_ITER 100000
 #define VIP_NUM 5
@@ -1177,6 +1208,7 @@ int main(void)
 {
 	test_pkt_access();
 	test_xdp();
+	test_xdp_adjust_tail();
 	test_l4lb_all();
 	test_xdp_noinline();
 	test_tcp_estats();