需要有关 XDP 程序因错误加载失败的帮助 "R4 min value is negative, either use unsigned or 'var &= const'"
Need help in XDP program failing to load with error "R4 min value is negative, either use unsigned or 'var &= const'"
我编写了一个 XDP 程序来查看传入的 TCP 数据包。
基本上我将目标 IPv4 地址交换到同一网络上的另一台服务器
观察：
如果我在函数中放置一个固定值而不是 tcp_len 变量，问题就会消失，或者如果我添加以下检查：
if(tcp_len > 20){
return XDP_PASS;
}
错误也消失了
我需要解决这个问题，我认为这个错误与我计算校验和的函数或我遗漏的一些其他细节有关
代码如下：
// SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
// Copyright (c) 2018 Netronome Systems, Inc.
#define BPF_NO_GLOBAL_DATA
#define MAX_PACKET_OFF 0xffff
#include <stdbool.h>
#include <stddef.h>
#include <string.h>
#include <linux/bpf.h>
#include <linux/icmp.h>
#include <linux/if_ether.h>
#include <linux/if_vlan.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/ipv6.h>
#include "bpf_endian.h"
#include "bpf_helpers.h"
#include "jhash.h"
#include <stdint.h>
#define htons(x) ((__be16)___constant_swab16((x)))
#define htonl(x) ((__be32)___constant_swab32((x)))
__attribute__((__always_inline__))
static inline __u16 csum_fold_helper(__u64 csum) {
int i;
#pragma unroll
for (i = 0; i < 4; i++) {
if (csum >> 16)
csum = (csum & 0xffff) + (csum >> 16);
}
return ~csum;
}
__attribute__((__always_inline__))
static inline void ipv4_csum(void* data_start, int data_size, __u64* csum) {
*csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
*csum = csum_fold_helper(*csum);
}
__attribute__((__always_inline__))
static inline void ipv4_l4_csum(void* data_start, __u32 data_size,
__u64* csum, struct iphdr* iph) {
__u32 tmp = 0;
*csum = bpf_csum_diff(0, 0, &iph->saddr, sizeof(__be32), *csum);
*csum = bpf_csum_diff(0, 0, &iph->daddr, sizeof(__be32), *csum);
tmp = __builtin_bswap32((__u32)(iph->protocol));
*csum = bpf_csum_diff(0, 0, &tmp, sizeof(__u32), *csum);
tmp = __builtin_bswap32((__u32)(data_size));
*csum = bpf_csum_diff(0, 0, &tmp, sizeof(__u32), *csum);
*csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
*csum = csum_fold_helper(*csum);
}
SEC("prog")
int xdp_drop_benchmark_traffic(struct xdp_md* ctx)
{
void* data_end = (void*)(long)ctx->data_end;
void* data = (void*)(long)ctx->data;
struct ethhdr* eth = data;
uint64_t nh_off = sizeof(*eth);
if (data + nh_off > data_end) {
return XDP_PASS;
}
uint16_t h_proto = eth->h_proto;
if (h_proto == htons(ETH_P_IP)) {
struct iphdr* iph = data + nh_off;
struct tcphdr* tcph = data + nh_off + sizeof(struct iphdr);
if (tcph + 1 > (struct tcphdr*)data_end || iph->protocol != IPPROTO_TCP){
return XDP_PASS;
}
__u16 tcp_len = htons(iph->tot_len) - (iph->ihl << 2);
if (tcp_len > MAX_PACKET_OFF) {
return XDP_DROP;
}
if (tcph->dest == htons(1234)) {
iph->saddr = iph->daddr;
iph->daddr = 4266428307;
__u64 csum = 0;
iph->check = 0;
ipv4_csum(iph, sizeof(struct iphdr), &csum);
iph->check = csum;
csum = 0;
tcph->check = 0;
bpf_debug("TCP Len: %i | %i\n", tcp_len, htonl(tcp_len));
ipv4_l4_csum(tcph, tcp_len, &csum, iph);
tcph->check = csum;
return XDP_TX;
}
}
return XDP_PASS;
}
char _license[] SEC("license") = "GPL";
日志：
libbpf: loading main.o
libbpf: elf: section(3) prog, size 1096, link 0, flags 6, type=1
libbpf: sec 'prog': found program 'xdp_drop_benchmark_traffic' at insn offset 0 (0 bytes), code size 137 insns (1096 bytes)
libbpf: elf: section(4) .rodata.str1.16, size 18, link 0, flags 32, type=1
libbpf: elf: skipping unrecognized data section(4) .rodata.str1.16
libbpf: elf: section(5) license, size 4, link 0, flags 3, type=1
libbpf: license of main.o is GPL
libbpf: elf: section(6) .eh_frame, size 48, link 0, flags 2, type=1
libbpf: elf: skipping unrecognized data section(6) .eh_frame
libbpf: elf: section(7) .rel.eh_frame, size 16, link 8, flags 0, type=9
libbpf: elf: skipping relo section(7) .rel.eh_frame for section(6) .eh_frame
libbpf: elf: section(8) .symtab, size 288, link 1, flags 0, type=2
libbpf: looking for externs among 12 symbols...
libbpf: collected 0 externs total
libbpf: prog 'xdp_drop_benchmark_traffic': unrecognized ELF section name 'prog'
libbpf: load bpf program failed: Permission denied
libbpf: -- BEGIN DUMP LOG ---
libbpf:
0: (b7) r0 = 2
1: (61) r2 = *(u32 *)(r1 +4)
2: (61) r7 = *(u32 *)(r1 +0)
3: (bf) r3 = r7
4: (07) r3 += 14
5: (2d) if r3 > r2 goto pc+130
R0_w=inv2 R1=ctx(id=0,off=0,imm=0) R2_w=pkt_end(id=0,off=0,imm=0) R3_w=pkt(id=0,off=14,r=14,imm=0) R7_w=pkt(id=0,off=0,r=14,imm=0) R10=fp0
6: (71) r1 = *(u8 *)(r7 +12)
7: (71) r4 = *(u8 *)(r7 +13)
8: (67) r4 <<= 8
9: (4f) r4 |= r1
10: (55) if r4 != 0x8 goto pc+125
R0_w=inv2 R1_w=inv(id=0,umax_value=255,var_off=(0x0; 0xff)) R2_w=pkt_end(id=0,off=0,imm=0) R3_w=pkt(id=0,off=14,r=14,imm=0) R4_w=inv8 R7_w=pkt(id=0,off=0,r=14,imm=0) R10=fp0
11: (bf) r1 = r7
12: (07) r1 += 54
13: (2d) if r1 > r2 goto pc+122
R0=inv2 R1=pkt(id=0,off=54,r=54,imm=0) R2=pkt_end(id=0,off=0,imm=0) R3=pkt(id=0,off=14,r=54,imm=0) R4=inv8 R7=pkt(id=0,off=0,r=54,imm=0) R10=fp0
14: (71) r1 = *(u8 *)(r7 +23)
15: (55) if r1 != 0x6 goto pc+120
R0=inv2 R1_w=inv6 R2=pkt_end(id=0,off=0,imm=0) R3=pkt(id=0,off=14,r=54,imm=0) R4=inv8 R7=pkt(id=0,off=0,r=54,imm=0) R10=fp0
16: (69) r1 = *(u16 *)(r7 +36)
17: (55) if r1 != 0xd204 goto pc+118
R0=inv2 R1_w=inv53764 R2=pkt_end(id=0,off=0,imm=0) R3=pkt(id=0,off=14,r=54,imm=0) R4=inv8 R7=pkt(id=0,off=0,r=54,imm=0) R10=fp0
18: (69) r6 = *(u16 *)(r7 +16)
19: (dc) r6 = be16 r6
20: (71) r9 = *(u8 *)(r7 +14)
21: (67) r9 <<= 2
22: (57) r9 &= 60
23: (61) r1 = *(u32 *)(r7 +30)
24: (18) r2 = 0xfe4c8793
26: (63) *(u32 *)(r7 +30) = r2
27: (63) *(u32 *)(r7 +26) = r1
28: (b7) r8 = 0
29: (6b) *(u16 *)(r7 +24) = r8
30: (b7) r1 = 0
31: (b7) r2 = 0
32: (b7) r4 = 20
33: (b7) r5 = 0
34: (85) call bpf_csum_diff#28
last_idx 34 first_idx 13
regs=4 stack=0 before 33: (b7) r5 = 0
regs=4 stack=0 before 32: (b7) r4 = 20
regs=4 stack=0 before 31: (b7) r2 = 0
last_idx 34 first_idx 13
regs=10 stack=0 before 33: (b7) r5 = 0
regs=10 stack=0 before 32: (b7) r4 = 20
35: (bf) r1 = r0
36: (77) r1 >>= 16
37: (15) if r1 == 0x0 goto pc+2
R0=inv(id=0) R1_w=inv(id=0,umax_value=281474976710655,var_off=(0x0; 0xffffffffffff)) R6=inv(id=0) R7=pkt(id=0,off=0,r=54,imm=0) R8=inv0 R9=inv(id=0,umax_value=60,var_off=(0x0; 0x3c)) R10=fp0
38: (57) r0 &= 65535
39: (0f) r0 += r1
40: (1f) r6 -= r9
41: (bf) r1 = r0
42: (77) r1 >>= 16
43: (15) if r1 == 0x0 goto pc+2
R0_w=inv(id=0,umax_value=281474976776190,var_off=(0x0; 0x1ffffffffffff)) R1_w=inv(id=0,umax_value=4294967296,var_off=(0x0; 0x1ffffffff)) R6_w=inv(id=0) R7=pkt(id=0,off=0,r=54,imm=0) R8=inv0 R9=inv(id=0,umax_value=60,var_off=(0x0; 0x3c)) R10=fp0
44: (57) r0 &= 65535
45: (0f) r0 += r1
46: (bf) r1 = r7
47: (07) r1 += 34
48: (7b) *(u64 *)(r10 -40) = r1
49: (57) r6 &= 65535
50: (bf) r1 = r0
51: (77) r1 >>= 16
52: (15) if r1 == 0x0 goto pc+2
R0=inv(id=0,umax_value=4295032831,var_off=(0x0; 0x1ffffffff)) R1_w=inv(id=0,umax_value=65536,var_off=(0x0; 0x1ffff)) R6_w=inv(id=0,umax_value=65535,var_off=(0x0; 0xffff)) R7=pkt(id=0,off=0,r=54,imm=0) R8=inv0 R9=inv(id=0,umax_value=60,var_off=(0x0; 0x3c)) R10=fp0 fp-40_w=pkt
53: (57) r0 &= 65535
54: (0f) r0 += r1
55: (bf) r1 = r0
56: (77) r1 >>= 16
57: (0f) r1 += r0
58: (a7) r1 ^= -1
59: (6b) *(u16 *)(r7 +24) = r1
60: (6b) *(u16 *)(r7 +50) = r8
61: (b7) r1 = 10
62: (6b) *(u16 *)(r10 -16) = r1
63: (18) r1 = 0x6925207c20692520
65: (7b) *(u64 *)(r10 -24) = r1
66: (18) r1 = 0x3a6e654c20504354
68: (7b) *(u64 *)(r10 -32) = r1
69: (bf) r8 = r6
70: (dc) r8 = be32 r8
71: (bf) r1 = r10
72: (07) r1 += -32
73: (b7) r2 = 18
74: (bf) r3 = r6
75: (bf) r4 = r8
76: (85) call bpf_trace_printk#6
last_idx 76 first_idx 46
regs=4 stack=0 before 75: (bf) r4 = r8
regs=4 stack=0 before 74: (bf) r3 = r6
regs=4 stack=0 before 73: (b7) r2 = 18
77: (bf) r3 = r7
78: (07) r3 += 26
79: (b7) r1 = 0
80: (b7) r2 = 0
81: (b7) r4 = 4
82: (b7) r5 = 0
83: (85) call bpf_csum_diff#28
last_idx 83 first_idx 77
regs=4 stack=0 before 82: (b7) r5 = 0
regs=4 stack=0 before 81: (b7) r4 = 4
regs=4 stack=0 before 80: (b7) r2 = 0
last_idx 83 first_idx 77
regs=10 stack=0 before 82: (b7) r5 = 0
regs=10 stack=0 before 81: (b7) r4 = 4
84: (bf) r3 = r7
85: (07) r3 += 30
86: (b7) r1 = 0
87: (b7) r2 = 0
88: (b7) r4 = 4
89: (bf) r5 = r0
90: (85) call bpf_csum_diff#28
last_idx 90 first_idx 77
regs=4 stack=0 before 89: (bf) r5 = r0
regs=4 stack=0 before 88: (b7) r4 = 4
regs=4 stack=0 before 87: (b7) r2 = 0
last_idx 90 first_idx 77
regs=10 stack=0 before 89: (bf) r5 = r0
regs=10 stack=0 before 88: (b7) r4 = 4
91: (71) r1 = *(u8 *)(r7 +23)
92: (dc) r1 = be32 r1
93: (63) *(u32 *)(r10 -32) = r1
94: (bf) r9 = r10
95: (07) r9 += -32
96: (b7) r1 = 0
97: (b7) r2 = 0
98: (bf) r3 = r9
99: (b7) r4 = 4
100: (bf) r5 = r0
101: (85) call bpf_csum_diff#28
last_idx 101 first_idx 91
regs=4 stack=0 before 100: (bf) r5 = r0
regs=4 stack=0 before 99: (b7) r4 = 4
regs=4 stack=0 before 98: (bf) r3 = r9
regs=4 stack=0 before 97: (b7) r2 = 0
last_idx 101 first_idx 91
regs=10 stack=0 before 100: (bf) r5 = r0
regs=10 stack=0 before 99: (b7) r4 = 4
102: (63) *(u32 *)(r10 -32) = r8
103: (b7) r1 = 0
104: (b7) r2 = 0
105: (bf) r3 = r9
106: (b7) r4 = 4
107: (bf) r5 = r0
108: (85) call bpf_csum_diff#28
last_idx 108 first_idx 91
regs=4 stack=0 before 107: (bf) r5 = r0
regs=4 stack=0 before 106: (b7) r4 = 4
regs=4 stack=0 before 105: (bf) r3 = r9
regs=4 stack=0 before 104: (b7) r2 = 0
last_idx 108 first_idx 91
regs=10 stack=0 before 107: (bf) r5 = r0
regs=10 stack=0 before 106: (b7) r4 = 4
109: (b7) r1 = 0
110: (b7) r2 = 0
111: (79) r3 = *(u64 *)(r10 -40)
112: (bf) r4 = r6
113: (bf) r5 = r0
114: (85) call bpf_csum_diff#28
last_idx 114 first_idx 109
regs=4 stack=0 before 113: (bf) r5 = r0
regs=4 stack=0 before 112: (bf) r4 = r6
regs=4 stack=0 before 111: (79) r3 = *(u64 *)(r10 -40)
regs=4 stack=0 before 110: (b7) r2 = 0
invalid access to packet, off=34 size=65535, R3(id=0,off=34,r=54)
R3 offset is outside of the packet
processed 112 insns (limit 1000000) max_states_per_insn 0 total_states 6 peak_states 6 mark_read 3
libbpf: -- END LOG --
libbpf: failed to load program 'xdp_drop_benchmark_traffic'
libbpf: failed to load object 'main.o'
Error fetching program/map!
我想了解我哪里出错了，正确的源代码是什么。
谢谢
TL;DR. 您正在尝试通过 bpf_csum_diff BPF 助手对数据包进行无限制访问。你应该绑定 tcp_len.
验证器错误解释
109: (b7) r1 = 0
110: (b7) r2 = 0
111: (79) r3 = *(u64 *)(r10 -40)
112: (bf) r4 = r6
113: (bf) r5 = r0
114: (85) call bpf_csum_diff#28
invalid access to packet, off=34 size=65535, R3(id=0,off=34,r=54)
R3 offset is outside of the packet
验证者抱怨说您正试图读取一个数据包中最多 65535 个字节，而这个数据包只知道至少有 54 个字节。此访问大小由 bpf_csum_diff 的第 4 个参数给出，通过 r4 传递。从 IP header.
读取后，您确实从未检查 r4 是否在数据包范围内
修复
您可以：
- 绑定
tcp_len 到已知的数据包大小。所以在你的情况下是 20，因为你在偏移量 34 处读取并且已知数据包长 54 个字节。
- 检查数据包是否足够大以容纳
tcp_len 的更大范围。您仍然需要绑定 tcp_len，因为 65535 已经是最大的数据包绑定，但您将能够有更大的 tcp_len 限制。
我编写了一个 XDP 程序来查看传入的 TCP 数据包。
基本上我将目标 IPv4 地址交换到同一网络上的另一台服务器
观察： 如果我在函数中放置一个固定值而不是 tcp_len 变量，问题就会消失，或者如果我添加以下检查：
if(tcp_len > 20){
return XDP_PASS;
}
错误也消失了
我需要解决这个问题，我认为这个错误与我计算校验和的函数或我遗漏的一些其他细节有关
代码如下：
// SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
// Copyright (c) 2018 Netronome Systems, Inc.
#define BPF_NO_GLOBAL_DATA
#define MAX_PACKET_OFF 0xffff
#include <stdbool.h>
#include <stddef.h>
#include <string.h>
#include <linux/bpf.h>
#include <linux/icmp.h>
#include <linux/if_ether.h>
#include <linux/if_vlan.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/ipv6.h>
#include "bpf_endian.h"
#include "bpf_helpers.h"
#include "jhash.h"
#include <stdint.h>
#define htons(x) ((__be16)___constant_swab16((x)))
#define htonl(x) ((__be32)___constant_swab32((x)))
__attribute__((__always_inline__))
static inline __u16 csum_fold_helper(__u64 csum) {
int i;
#pragma unroll
for (i = 0; i < 4; i++) {
if (csum >> 16)
csum = (csum & 0xffff) + (csum >> 16);
}
return ~csum;
}
__attribute__((__always_inline__))
static inline void ipv4_csum(void* data_start, int data_size, __u64* csum) {
*csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
*csum = csum_fold_helper(*csum);
}
__attribute__((__always_inline__))
static inline void ipv4_l4_csum(void* data_start, __u32 data_size,
__u64* csum, struct iphdr* iph) {
__u32 tmp = 0;
*csum = bpf_csum_diff(0, 0, &iph->saddr, sizeof(__be32), *csum);
*csum = bpf_csum_diff(0, 0, &iph->daddr, sizeof(__be32), *csum);
tmp = __builtin_bswap32((__u32)(iph->protocol));
*csum = bpf_csum_diff(0, 0, &tmp, sizeof(__u32), *csum);
tmp = __builtin_bswap32((__u32)(data_size));
*csum = bpf_csum_diff(0, 0, &tmp, sizeof(__u32), *csum);
*csum = bpf_csum_diff(0, 0, data_start, data_size, *csum);
*csum = csum_fold_helper(*csum);
}
SEC("prog")
int xdp_drop_benchmark_traffic(struct xdp_md* ctx)
{
void* data_end = (void*)(long)ctx->data_end;
void* data = (void*)(long)ctx->data;
struct ethhdr* eth = data;
uint64_t nh_off = sizeof(*eth);
if (data + nh_off > data_end) {
return XDP_PASS;
}
uint16_t h_proto = eth->h_proto;
if (h_proto == htons(ETH_P_IP)) {
struct iphdr* iph = data + nh_off;
struct tcphdr* tcph = data + nh_off + sizeof(struct iphdr);
if (tcph + 1 > (struct tcphdr*)data_end || iph->protocol != IPPROTO_TCP){
return XDP_PASS;
}
__u16 tcp_len = htons(iph->tot_len) - (iph->ihl << 2);
if (tcp_len > MAX_PACKET_OFF) {
return XDP_DROP;
}
if (tcph->dest == htons(1234)) {
iph->saddr = iph->daddr;
iph->daddr = 4266428307;
__u64 csum = 0;
iph->check = 0;
ipv4_csum(iph, sizeof(struct iphdr), &csum);
iph->check = csum;
csum = 0;
tcph->check = 0;
bpf_debug("TCP Len: %i | %i\n", tcp_len, htonl(tcp_len));
ipv4_l4_csum(tcph, tcp_len, &csum, iph);
tcph->check = csum;
return XDP_TX;
}
}
return XDP_PASS;
}
char _license[] SEC("license") = "GPL";
日志：
libbpf: loading main.o
libbpf: elf: section(3) prog, size 1096, link 0, flags 6, type=1
libbpf: sec 'prog': found program 'xdp_drop_benchmark_traffic' at insn offset 0 (0 bytes), code size 137 insns (1096 bytes)
libbpf: elf: section(4) .rodata.str1.16, size 18, link 0, flags 32, type=1
libbpf: elf: skipping unrecognized data section(4) .rodata.str1.16
libbpf: elf: section(5) license, size 4, link 0, flags 3, type=1
libbpf: license of main.o is GPL
libbpf: elf: section(6) .eh_frame, size 48, link 0, flags 2, type=1
libbpf: elf: skipping unrecognized data section(6) .eh_frame
libbpf: elf: section(7) .rel.eh_frame, size 16, link 8, flags 0, type=9
libbpf: elf: skipping relo section(7) .rel.eh_frame for section(6) .eh_frame
libbpf: elf: section(8) .symtab, size 288, link 1, flags 0, type=2
libbpf: looking for externs among 12 symbols...
libbpf: collected 0 externs total
libbpf: prog 'xdp_drop_benchmark_traffic': unrecognized ELF section name 'prog'
libbpf: load bpf program failed: Permission denied
libbpf: -- BEGIN DUMP LOG ---
libbpf:
0: (b7) r0 = 2
1: (61) r2 = *(u32 *)(r1 +4)
2: (61) r7 = *(u32 *)(r1 +0)
3: (bf) r3 = r7
4: (07) r3 += 14
5: (2d) if r3 > r2 goto pc+130
R0_w=inv2 R1=ctx(id=0,off=0,imm=0) R2_w=pkt_end(id=0,off=0,imm=0) R3_w=pkt(id=0,off=14,r=14,imm=0) R7_w=pkt(id=0,off=0,r=14,imm=0) R10=fp0
6: (71) r1 = *(u8 *)(r7 +12)
7: (71) r4 = *(u8 *)(r7 +13)
8: (67) r4 <<= 8
9: (4f) r4 |= r1
10: (55) if r4 != 0x8 goto pc+125
R0_w=inv2 R1_w=inv(id=0,umax_value=255,var_off=(0x0; 0xff)) R2_w=pkt_end(id=0,off=0,imm=0) R3_w=pkt(id=0,off=14,r=14,imm=0) R4_w=inv8 R7_w=pkt(id=0,off=0,r=14,imm=0) R10=fp0
11: (bf) r1 = r7
12: (07) r1 += 54
13: (2d) if r1 > r2 goto pc+122
R0=inv2 R1=pkt(id=0,off=54,r=54,imm=0) R2=pkt_end(id=0,off=0,imm=0) R3=pkt(id=0,off=14,r=54,imm=0) R4=inv8 R7=pkt(id=0,off=0,r=54,imm=0) R10=fp0
14: (71) r1 = *(u8 *)(r7 +23)
15: (55) if r1 != 0x6 goto pc+120
R0=inv2 R1_w=inv6 R2=pkt_end(id=0,off=0,imm=0) R3=pkt(id=0,off=14,r=54,imm=0) R4=inv8 R7=pkt(id=0,off=0,r=54,imm=0) R10=fp0
16: (69) r1 = *(u16 *)(r7 +36)
17: (55) if r1 != 0xd204 goto pc+118
R0=inv2 R1_w=inv53764 R2=pkt_end(id=0,off=0,imm=0) R3=pkt(id=0,off=14,r=54,imm=0) R4=inv8 R7=pkt(id=0,off=0,r=54,imm=0) R10=fp0
18: (69) r6 = *(u16 *)(r7 +16)
19: (dc) r6 = be16 r6
20: (71) r9 = *(u8 *)(r7 +14)
21: (67) r9 <<= 2
22: (57) r9 &= 60
23: (61) r1 = *(u32 *)(r7 +30)
24: (18) r2 = 0xfe4c8793
26: (63) *(u32 *)(r7 +30) = r2
27: (63) *(u32 *)(r7 +26) = r1
28: (b7) r8 = 0
29: (6b) *(u16 *)(r7 +24) = r8
30: (b7) r1 = 0
31: (b7) r2 = 0
32: (b7) r4 = 20
33: (b7) r5 = 0
34: (85) call bpf_csum_diff#28
last_idx 34 first_idx 13
regs=4 stack=0 before 33: (b7) r5 = 0
regs=4 stack=0 before 32: (b7) r4 = 20
regs=4 stack=0 before 31: (b7) r2 = 0
last_idx 34 first_idx 13
regs=10 stack=0 before 33: (b7) r5 = 0
regs=10 stack=0 before 32: (b7) r4 = 20
35: (bf) r1 = r0
36: (77) r1 >>= 16
37: (15) if r1 == 0x0 goto pc+2
R0=inv(id=0) R1_w=inv(id=0,umax_value=281474976710655,var_off=(0x0; 0xffffffffffff)) R6=inv(id=0) R7=pkt(id=0,off=0,r=54,imm=0) R8=inv0 R9=inv(id=0,umax_value=60,var_off=(0x0; 0x3c)) R10=fp0
38: (57) r0 &= 65535
39: (0f) r0 += r1
40: (1f) r6 -= r9
41: (bf) r1 = r0
42: (77) r1 >>= 16
43: (15) if r1 == 0x0 goto pc+2
R0_w=inv(id=0,umax_value=281474976776190,var_off=(0x0; 0x1ffffffffffff)) R1_w=inv(id=0,umax_value=4294967296,var_off=(0x0; 0x1ffffffff)) R6_w=inv(id=0) R7=pkt(id=0,off=0,r=54,imm=0) R8=inv0 R9=inv(id=0,umax_value=60,var_off=(0x0; 0x3c)) R10=fp0
44: (57) r0 &= 65535
45: (0f) r0 += r1
46: (bf) r1 = r7
47: (07) r1 += 34
48: (7b) *(u64 *)(r10 -40) = r1
49: (57) r6 &= 65535
50: (bf) r1 = r0
51: (77) r1 >>= 16
52: (15) if r1 == 0x0 goto pc+2
R0=inv(id=0,umax_value=4295032831,var_off=(0x0; 0x1ffffffff)) R1_w=inv(id=0,umax_value=65536,var_off=(0x0; 0x1ffff)) R6_w=inv(id=0,umax_value=65535,var_off=(0x0; 0xffff)) R7=pkt(id=0,off=0,r=54,imm=0) R8=inv0 R9=inv(id=0,umax_value=60,var_off=(0x0; 0x3c)) R10=fp0 fp-40_w=pkt
53: (57) r0 &= 65535
54: (0f) r0 += r1
55: (bf) r1 = r0
56: (77) r1 >>= 16
57: (0f) r1 += r0
58: (a7) r1 ^= -1
59: (6b) *(u16 *)(r7 +24) = r1
60: (6b) *(u16 *)(r7 +50) = r8
61: (b7) r1 = 10
62: (6b) *(u16 *)(r10 -16) = r1
63: (18) r1 = 0x6925207c20692520
65: (7b) *(u64 *)(r10 -24) = r1
66: (18) r1 = 0x3a6e654c20504354
68: (7b) *(u64 *)(r10 -32) = r1
69: (bf) r8 = r6
70: (dc) r8 = be32 r8
71: (bf) r1 = r10
72: (07) r1 += -32
73: (b7) r2 = 18
74: (bf) r3 = r6
75: (bf) r4 = r8
76: (85) call bpf_trace_printk#6
last_idx 76 first_idx 46
regs=4 stack=0 before 75: (bf) r4 = r8
regs=4 stack=0 before 74: (bf) r3 = r6
regs=4 stack=0 before 73: (b7) r2 = 18
77: (bf) r3 = r7
78: (07) r3 += 26
79: (b7) r1 = 0
80: (b7) r2 = 0
81: (b7) r4 = 4
82: (b7) r5 = 0
83: (85) call bpf_csum_diff#28
last_idx 83 first_idx 77
regs=4 stack=0 before 82: (b7) r5 = 0
regs=4 stack=0 before 81: (b7) r4 = 4
regs=4 stack=0 before 80: (b7) r2 = 0
last_idx 83 first_idx 77
regs=10 stack=0 before 82: (b7) r5 = 0
regs=10 stack=0 before 81: (b7) r4 = 4
84: (bf) r3 = r7
85: (07) r3 += 30
86: (b7) r1 = 0
87: (b7) r2 = 0
88: (b7) r4 = 4
89: (bf) r5 = r0
90: (85) call bpf_csum_diff#28
last_idx 90 first_idx 77
regs=4 stack=0 before 89: (bf) r5 = r0
regs=4 stack=0 before 88: (b7) r4 = 4
regs=4 stack=0 before 87: (b7) r2 = 0
last_idx 90 first_idx 77
regs=10 stack=0 before 89: (bf) r5 = r0
regs=10 stack=0 before 88: (b7) r4 = 4
91: (71) r1 = *(u8 *)(r7 +23)
92: (dc) r1 = be32 r1
93: (63) *(u32 *)(r10 -32) = r1
94: (bf) r9 = r10
95: (07) r9 += -32
96: (b7) r1 = 0
97: (b7) r2 = 0
98: (bf) r3 = r9
99: (b7) r4 = 4
100: (bf) r5 = r0
101: (85) call bpf_csum_diff#28
last_idx 101 first_idx 91
regs=4 stack=0 before 100: (bf) r5 = r0
regs=4 stack=0 before 99: (b7) r4 = 4
regs=4 stack=0 before 98: (bf) r3 = r9
regs=4 stack=0 before 97: (b7) r2 = 0
last_idx 101 first_idx 91
regs=10 stack=0 before 100: (bf) r5 = r0
regs=10 stack=0 before 99: (b7) r4 = 4
102: (63) *(u32 *)(r10 -32) = r8
103: (b7) r1 = 0
104: (b7) r2 = 0
105: (bf) r3 = r9
106: (b7) r4 = 4
107: (bf) r5 = r0
108: (85) call bpf_csum_diff#28
last_idx 108 first_idx 91
regs=4 stack=0 before 107: (bf) r5 = r0
regs=4 stack=0 before 106: (b7) r4 = 4
regs=4 stack=0 before 105: (bf) r3 = r9
regs=4 stack=0 before 104: (b7) r2 = 0
last_idx 108 first_idx 91
regs=10 stack=0 before 107: (bf) r5 = r0
regs=10 stack=0 before 106: (b7) r4 = 4
109: (b7) r1 = 0
110: (b7) r2 = 0
111: (79) r3 = *(u64 *)(r10 -40)
112: (bf) r4 = r6
113: (bf) r5 = r0
114: (85) call bpf_csum_diff#28
last_idx 114 first_idx 109
regs=4 stack=0 before 113: (bf) r5 = r0
regs=4 stack=0 before 112: (bf) r4 = r6
regs=4 stack=0 before 111: (79) r3 = *(u64 *)(r10 -40)
regs=4 stack=0 before 110: (b7) r2 = 0
invalid access to packet, off=34 size=65535, R3(id=0,off=34,r=54)
R3 offset is outside of the packet
processed 112 insns (limit 1000000) max_states_per_insn 0 total_states 6 peak_states 6 mark_read 3
libbpf: -- END LOG --
libbpf: failed to load program 'xdp_drop_benchmark_traffic'
libbpf: failed to load object 'main.o'
Error fetching program/map!
我想了解我哪里出错了，正确的源代码是什么。
谢谢
TL;DR. 您正在尝试通过 bpf_csum_diff BPF 助手对数据包进行无限制访问。你应该绑定 tcp_len.
验证器错误解释
109: (b7) r1 = 0
110: (b7) r2 = 0
111: (79) r3 = *(u64 *)(r10 -40)
112: (bf) r4 = r6
113: (bf) r5 = r0
114: (85) call bpf_csum_diff#28
invalid access to packet, off=34 size=65535, R3(id=0,off=34,r=54)
R3 offset is outside of the packet
验证者抱怨说您正试图读取一个数据包中最多 65535 个字节，而这个数据包只知道至少有 54 个字节。此访问大小由 bpf_csum_diff 的第 4 个参数给出，通过 r4 传递。从 IP header.
r4 是否在数据包范围内
修复
您可以：
- 绑定
tcp_len到已知的数据包大小。所以在你的情况下是 20，因为你在偏移量 34 处读取并且已知数据包长 54 个字节。 - 检查数据包是否足够大以容纳
tcp_len的更大范围。您仍然需要绑定tcp_len，因为 65535 已经是最大的数据包绑定，但您将能够有更大的tcp_len限制。