mirror of
https://github.com/torvalds/linux
synced 2024-11-05 18:23:50 +00:00
e2e3224122
Improve the 'unknown reason' comment, with an actual explaination of why
the ctx pkt-data pointers need to be loaded after the helper function
bpf_xdp_adjust_meta(). Based on the explaination Daniel gave.
Fixes: 36e04a2d78 ("samples/bpf: xdp2skb_meta shows transferring info from XDP to SKB")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
105 lines
3 KiB
C
105 lines
3 KiB
C
/* SPDX-License-Identifier: GPL-2.0
|
|
* Copyright (c) 2018 Jesper Dangaard Brouer, Red Hat Inc.
|
|
*
|
|
* Example howto transfer info from XDP to SKB, e.g. skb->mark
|
|
* -----------------------------------------------------------
|
|
* This uses the XDP data_meta infrastructure, and is a cooperation
|
|
* between two bpf-programs (1) XDP and (2) clsact at TC-ingress hook.
|
|
*
|
|
* Notice: This example does not use the BPF C-loader (bpf_load.c),
|
|
* but instead rely on the iproute2 TC tool for loading BPF-objects.
|
|
*/
|
|
#include <uapi/linux/bpf.h>
|
|
#include <uapi/linux/pkt_cls.h>
|
|
|
|
#include "bpf_helpers.h"
|
|
|
|
/*
|
|
* This struct is stored in the XDP 'data_meta' area, which is located
|
|
* just in-front-of the raw packet payload data. The meaning is
|
|
* specific to these two BPF programs that use it as a communication
|
|
* channel. XDP adjust/increase the area via a bpf-helper, and TC use
|
|
* boundary checks to see if data have been provided.
|
|
*
|
|
* The struct must be 4 byte aligned, which here is enforced by the
|
|
* struct __attribute__((aligned(4))).
|
|
*/
|
|
struct meta_info {
|
|
__u32 mark;
|
|
} __attribute__((aligned(4)));
|
|
|
|
SEC("xdp_mark")
|
|
int _xdp_mark(struct xdp_md *ctx)
|
|
{
|
|
struct meta_info *meta;
|
|
void *data, *data_end;
|
|
int ret;
|
|
|
|
/* Reserve space in-front of data pointer for our meta info.
|
|
* (Notice drivers not supporting data_meta will fail here!)
|
|
*/
|
|
ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(*meta));
|
|
if (ret < 0)
|
|
return XDP_ABORTED;
|
|
|
|
/* Notice: Kernel-side verifier requires that loading of
|
|
* ctx->data MUST happen _after_ helper bpf_xdp_adjust_meta(),
|
|
* as pkt-data pointers are invalidated. Helpers that require
|
|
* this are determined/marked by bpf_helper_changes_pkt_data()
|
|
*/
|
|
data = (void *)(unsigned long)ctx->data;
|
|
|
|
/* Check data_meta have room for meta_info struct */
|
|
meta = (void *)(unsigned long)ctx->data_meta;
|
|
if (meta + 1 > data)
|
|
return XDP_ABORTED;
|
|
|
|
meta->mark = 42;
|
|
|
|
return XDP_PASS;
|
|
}
|
|
|
|
SEC("tc_mark")
|
|
int _tc_mark(struct __sk_buff *ctx)
|
|
{
|
|
void *data = (void *)(unsigned long)ctx->data;
|
|
void *data_end = (void *)(unsigned long)ctx->data_end;
|
|
void *data_meta = (void *)(unsigned long)ctx->data_meta;
|
|
struct meta_info *meta = data_meta;
|
|
|
|
/* Check XDP gave us some data_meta */
|
|
if (meta + 1 > data) {
|
|
ctx->mark = 41;
|
|
/* Skip "accept" if no data_meta is avail */
|
|
return TC_ACT_OK;
|
|
}
|
|
|
|
/* Hint: See func tc_cls_act_is_valid_access() for BPF_WRITE access */
|
|
ctx->mark = meta->mark; /* Transfer XDP-mark to SKB-mark */
|
|
|
|
return TC_ACT_OK;
|
|
}
|
|
|
|
/* Manually attaching these programs:
|
|
export DEV=ixgbe2
|
|
export FILE=xdp2skb_meta_kern.o
|
|
|
|
# via TC command
|
|
tc qdisc del dev $DEV clsact 2> /dev/null
|
|
tc qdisc add dev $DEV clsact
|
|
tc filter add dev $DEV ingress prio 1 handle 1 bpf da obj $FILE sec tc_mark
|
|
tc filter show dev $DEV ingress
|
|
|
|
# XDP via IP command:
|
|
ip link set dev $DEV xdp off
|
|
ip link set dev $DEV xdp obj $FILE sec xdp_mark
|
|
|
|
# Use iptable to "see" if SKBs are marked
|
|
iptables -I INPUT -p icmp -m mark --mark 41 # == 0x29
|
|
iptables -I INPUT -p icmp -m mark --mark 42 # == 0x2a
|
|
|
|
# Hint: catch XDP_ABORTED errors via
|
|
perf record -e xdp:*
|
|
perf script
|
|
|
|
*/
|