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 BPF_PACKET_HEADER __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 next_header; 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, &pad_size, &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, 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, (srh->hdrlen+1) << 3, 244 (struct sr6_tlv_t *)&tlv, 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