1 | #include <stddef.h> |
2 | #include <inttypes.h> |
3 | #include <errno.h> |
4 | #include <linux/seg6_local.h> |
5 | #include <linux/bpf.h> |
6 | #include <bpf/bpf_helpers.h> |
7 | #include <bpf/bpf_endian.h> |
8 | |
9 | #include "bpf_compiler.h" |
10 | |
11 | /* Packet parsing state machine helpers. */ |
12 | #define cursor_advance(_cursor, _len) \ |
13 | ({ void *_tmp = _cursor; _cursor += _len; _tmp; }) |
14 | |
15 | #define SR6_FLAG_ALERT (1 << 4) |
16 | |
17 | #define __attribute__((packed)) |
18 | |
19 | struct ip6_t { |
20 | unsigned int ver:4; |
21 | unsigned int priority:8; |
22 | unsigned int flow_label:20; |
23 | unsigned short payload_len; |
24 | unsigned char ; |
25 | unsigned char hop_limit; |
26 | unsigned long long src_hi; |
27 | unsigned long long src_lo; |
28 | unsigned long long dst_hi; |
29 | unsigned long long dst_lo; |
30 | } BPF_PACKET_HEADER; |
31 | |
32 | struct ip6_addr_t { |
33 | unsigned long long hi; |
34 | unsigned long long lo; |
35 | } BPF_PACKET_HEADER; |
36 | |
37 | struct ip6_srh_t { |
38 | unsigned char nexthdr; |
39 | unsigned char hdrlen; |
40 | unsigned char type; |
41 | unsigned char segments_left; |
42 | unsigned char first_segment; |
43 | unsigned char flags; |
44 | unsigned short tag; |
45 | |
46 | struct ip6_addr_t segments[0]; |
47 | } BPF_PACKET_HEADER; |
48 | |
49 | struct sr6_tlv_t { |
50 | unsigned char type; |
51 | unsigned char len; |
52 | unsigned char value[0]; |
53 | } BPF_PACKET_HEADER; |
54 | |
55 | static __always_inline struct ip6_srh_t *get_srh(struct __sk_buff *skb) |
56 | { |
57 | void *cursor, *data_end; |
58 | struct ip6_srh_t *srh; |
59 | struct ip6_t *ip; |
60 | uint8_t *ipver; |
61 | |
62 | data_end = (void *)(long)skb->data_end; |
63 | cursor = (void *)(long)skb->data; |
64 | ipver = (uint8_t *)cursor; |
65 | |
66 | if ((void *)ipver + sizeof(*ipver) > data_end) |
67 | return NULL; |
68 | |
69 | if ((*ipver >> 4) != 6) |
70 | return NULL; |
71 | |
72 | ip = cursor_advance(cursor, sizeof(*ip)); |
73 | if ((void *)ip + sizeof(*ip) > data_end) |
74 | return NULL; |
75 | |
76 | if (ip->next_header != 43) |
77 | return NULL; |
78 | |
79 | srh = cursor_advance(cursor, sizeof(*srh)); |
80 | if ((void *)srh + sizeof(*srh) > data_end) |
81 | return NULL; |
82 | |
83 | if (srh->type != 4) |
84 | return NULL; |
85 | |
86 | return srh; |
87 | } |
88 | |
89 | static __always_inline int update_tlv_pad(struct __sk_buff *skb, |
90 | uint32_t new_pad, uint32_t old_pad, |
91 | uint32_t pad_off) |
92 | { |
93 | int err; |
94 | |
95 | if (new_pad != old_pad) { |
96 | err = bpf_lwt_seg6_adjust_srh(skb, pad_off, |
97 | (int) new_pad - (int) old_pad); |
98 | if (err) |
99 | return err; |
100 | } |
101 | |
102 | if (new_pad > 0) { |
103 | char pad_tlv_buf[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, |
104 | 0, 0, 0}; |
105 | struct sr6_tlv_t *pad_tlv = (struct sr6_tlv_t *) pad_tlv_buf; |
106 | |
107 | pad_tlv->type = SR6_TLV_PADDING; |
108 | pad_tlv->len = new_pad - 2; |
109 | |
110 | err = bpf_lwt_seg6_store_bytes(skb, pad_off, |
111 | (void *)pad_tlv_buf, new_pad); |
112 | if (err) |
113 | return err; |
114 | } |
115 | |
116 | return 0; |
117 | } |
118 | |
119 | static __always_inline int is_valid_tlv_boundary(struct __sk_buff *skb, |
120 | struct ip6_srh_t *srh, |
121 | uint32_t *tlv_off, |
122 | uint32_t *pad_size, |
123 | uint32_t *pad_off) |
124 | { |
125 | uint32_t srh_off, cur_off; |
126 | int offset_valid = 0; |
127 | int err; |
128 | |
129 | srh_off = (char *)srh - (char *)(long)skb->data; |
130 | // cur_off = end of segments, start of possible TLVs |
131 | cur_off = srh_off + sizeof(*srh) + |
132 | sizeof(struct ip6_addr_t) * (srh->first_segment + 1); |
133 | |
134 | *pad_off = 0; |
135 | |
136 | // we can only go as far as ~10 TLVs due to the BPF max stack size |
137 | // workaround: define induction variable "i" as "long" instead |
138 | // of "int" to prevent alu32 sub-register spilling. |
139 | __pragma_loop_no_unroll |
140 | for (long i = 0; i < 100; i++) { |
141 | struct sr6_tlv_t tlv; |
142 | |
143 | if (cur_off == *tlv_off) |
144 | offset_valid = 1; |
145 | |
146 | if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3)) |
147 | break; |
148 | |
149 | err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv)); |
150 | if (err) |
151 | return err; |
152 | |
153 | if (tlv.type == SR6_TLV_PADDING) { |
154 | *pad_size = tlv.len + sizeof(tlv); |
155 | *pad_off = cur_off; |
156 | |
157 | if (*tlv_off == srh_off) { |
158 | *tlv_off = cur_off; |
159 | offset_valid = 1; |
160 | } |
161 | break; |
162 | |
163 | } else if (tlv.type == SR6_TLV_HMAC) { |
164 | break; |
165 | } |
166 | |
167 | cur_off += sizeof(tlv) + tlv.len; |
168 | } // we reached the padding or HMAC TLVs, or the end of the SRH |
169 | |
170 | if (*pad_off == 0) |
171 | *pad_off = cur_off; |
172 | |
173 | if (*tlv_off == -1) |
174 | *tlv_off = cur_off; |
175 | else if (!offset_valid) |
176 | return -EINVAL; |
177 | |
178 | return 0; |
179 | } |
180 | |
181 | static __always_inline int add_tlv(struct __sk_buff *skb, |
182 | struct ip6_srh_t *srh, uint32_t tlv_off, |
183 | struct sr6_tlv_t *itlv, uint8_t tlv_size) |
184 | { |
185 | uint32_t srh_off = (char *)srh - (char *)(long)skb->data; |
186 | uint8_t len_remaining, new_pad; |
187 | uint32_t pad_off = 0; |
188 | uint32_t pad_size = 0; |
189 | uint32_t partial_srh_len; |
190 | int err; |
191 | |
192 | if (tlv_off != -1) |
193 | tlv_off += srh_off; |
194 | |
195 | if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC) |
196 | return -EINVAL; |
197 | |
198 | err = is_valid_tlv_boundary(skb, srh, tlv_off: &tlv_off, pad_size: &pad_size, pad_off: &pad_off); |
199 | if (err) |
200 | return err; |
201 | |
202 | err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len); |
203 | if (err) |
204 | return err; |
205 | |
206 | err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size); |
207 | if (err) |
208 | return err; |
209 | |
210 | // the following can't be moved inside update_tlv_pad because the |
211 | // bpf verifier has some issues with it |
212 | pad_off += sizeof(*itlv) + itlv->len; |
213 | partial_srh_len = pad_off - srh_off; |
214 | len_remaining = partial_srh_len % 8; |
215 | new_pad = 8 - len_remaining; |
216 | |
217 | if (new_pad == 1) // cannot pad for 1 byte only |
218 | new_pad = 9; |
219 | else if (new_pad == 8) |
220 | new_pad = 0; |
221 | |
222 | return update_tlv_pad(skb, new_pad, old_pad: pad_size, pad_off); |
223 | } |
224 | |
225 | // Add an Egress TLV fc00::4, add the flag A, |
226 | // and apply End.X action to fc42::1 |
227 | SEC("lwt_seg6local" ) |
228 | int __add_egr_x(struct __sk_buff *skb) |
229 | { |
230 | unsigned long long hi = 0xfc42000000000000; |
231 | unsigned long long lo = 0x1; |
232 | struct ip6_srh_t *srh = get_srh(skb); |
233 | uint8_t new_flags = SR6_FLAG_ALERT; |
234 | struct ip6_addr_t addr; |
235 | int err, offset; |
236 | |
237 | if (srh == NULL) |
238 | return BPF_DROP; |
239 | |
240 | uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, |
241 | 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4}; |
242 | |
243 | err = add_tlv(skb, srh, tlv_off: (srh->hdrlen+1) << 3, |
244 | itlv: (struct sr6_tlv_t *)&tlv, tlv_size: 20); |
245 | if (err) |
246 | return BPF_DROP; |
247 | |
248 | offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags); |
249 | err = bpf_lwt_seg6_store_bytes(skb, offset, |
250 | (void *)&new_flags, sizeof(new_flags)); |
251 | if (err) |
252 | return BPF_DROP; |
253 | |
254 | addr.lo = bpf_cpu_to_be64(lo); |
255 | addr.hi = bpf_cpu_to_be64(hi); |
256 | err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X, |
257 | (void *)&addr, sizeof(addr)); |
258 | if (err) |
259 | return BPF_DROP; |
260 | return BPF_REDIRECT; |
261 | } |
262 | char __license[] SEC("license" ) = "GPL" ; |
263 | |