1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright (c) 2019 Facebook
3 #include <linux/bpf.h>
4 #include <stdbool.h>
5 #include <bpf/bpf_helpers.h>
6 #include <bpf/bpf_endian.h>
7 #include <bpf/bpf_tracing.h>
8 
9 char _license[] SEC("license") = "GPL";
10 struct {
11 	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
12 	__uint(key_size, sizeof(int));
13 	__uint(value_size, sizeof(int));
14 } perf_buf_map SEC(".maps");
15 
16 #define _(P) (__builtin_preserve_access_index(P))
17 
18 /* define few struct-s that bpf program needs to access */
19 struct callback_head {
20 	struct callback_head *next;
21 	void (*func)(struct callback_head *head);
22 };
23 struct dev_ifalias {
24 	struct callback_head rcuhead;
25 };
26 
27 struct net_device /* same as kernel's struct net_device */ {
28 	int ifindex;
29 	struct dev_ifalias *ifalias;
30 };
31 
32 typedef struct {
33         int counter;
34 } atomic_t;
35 typedef struct refcount_struct {
36         atomic_t refs;
37 } refcount_t;
38 
39 struct sk_buff {
40 	/* field names and sizes should match to those in the kernel */
41 	unsigned int len, data_len;
42 	__u16 mac_len, hdr_len, queue_mapping;
43 	struct net_device *dev;
44 	/* order of the fields doesn't matter */
45 	refcount_t users;
46 	unsigned char *data;
47 	char __pkt_type_offset[0];
48 	char cb[48];
49 };
50 
51 struct meta {
52 	int ifindex;
53 	__u32 cb32_0;
54 	__u8 cb8_0;
55 };
56 
57 /* TRACE_EVENT(kfree_skb,
58  *         TP_PROTO(struct sk_buff *skb, void *location),
59  */
60 SEC("tp_btf/kfree_skb")
61 int BPF_PROG(trace_kfree_skb, struct sk_buff *skb, void *location)
62 {
63 	struct net_device *dev;
64 	struct callback_head *ptr;
65 	void *func;
66 	int users;
67 	unsigned char *data;
68 	unsigned short pkt_data;
69 	struct meta meta = {};
70 	char pkt_type;
71 	__u32 *cb32;
72 	__u8 *cb8;
73 
74 	__builtin_preserve_access_index(({
75 		users = skb->users.refs.counter;
76 		data = skb->data;
77 		dev = skb->dev;
78 		ptr = dev->ifalias->rcuhead.next;
79 		func = ptr->func;
80 		cb8 = (__u8 *)&skb->cb;
81 		cb32 = (__u32 *)&skb->cb;
82 	}));
83 
84 	meta.ifindex = _(dev->ifindex);
85 	meta.cb8_0 = cb8[8];
86 	meta.cb32_0 = cb32[2];
87 
88 	bpf_probe_read_kernel(&pkt_type, sizeof(pkt_type), _(&skb->__pkt_type_offset));
89 	pkt_type &= 7;
90 
91 	/* read eth proto */
92 	bpf_probe_read_kernel(&pkt_data, sizeof(pkt_data), data + 12);
93 
94 	bpf_printk("rcuhead.next %llx func %llx\n", ptr, func);
95 	bpf_printk("skb->len %d users %d pkt_type %x\n",
96 		   _(skb->len), users, pkt_type);
97 	bpf_printk("skb->queue_mapping %d\n", _(skb->queue_mapping));
98 	bpf_printk("dev->ifindex %d data %llx pkt_data %x\n",
99 		   meta.ifindex, data, pkt_data);
100 	bpf_printk("cb8_0:%x cb32_0:%x\n", meta.cb8_0, meta.cb32_0);
101 
102 	if (users != 1 || pkt_data != bpf_htons(0x86dd) || meta.ifindex != 1)
103 		/* raw tp ignores return value */
104 		return 0;
105 
106 	/* send first 72 byte of the packet to user space */
107 	bpf_skb_output(skb, &perf_buf_map, (72ull << 32) | BPF_F_CURRENT_CPU,
108 		       &meta, sizeof(meta));
109 	return 0;
110 }
111 
112 struct {
113 	bool fentry_test_ok;
114 	bool fexit_test_ok;
115 } result = {};
116 
117 SEC("fentry/eth_type_trans")
118 int BPF_PROG(fentry_eth_type_trans, struct sk_buff *skb, struct net_device *dev,
119 	     unsigned short protocol)
120 {
121 	int len, ifindex;
122 
123 	__builtin_preserve_access_index(({
124 		len = skb->len;
125 		ifindex = dev->ifindex;
126 	}));
127 
128 	/* fentry sees full packet including L2 header */
129 	if (len != 74 || ifindex != 1)
130 		return 0;
131 	result.fentry_test_ok = true;
132 	return 0;
133 }
134 
135 SEC("fexit/eth_type_trans")
136 int BPF_PROG(fexit_eth_type_trans, struct sk_buff *skb, struct net_device *dev,
137 	     unsigned short protocol)
138 {
139 	int len, ifindex;
140 
141 	__builtin_preserve_access_index(({
142 		len = skb->len;
143 		ifindex = dev->ifindex;
144 	}));
145 
146 	/* fexit sees packet without L2 header that eth_type_trans should have
147 	 * consumed.
148 	 */
149 	if (len != 60 || protocol != bpf_htons(0x86dd) || ifindex != 1)
150 		return 0;
151 	result.fexit_test_ok = true;
152 	return 0;
153 }
154