root/tools/testing/selftests/bpf/progs/test_lwt_seg6local.c

DEFINITIONS

1. get_srh
2. update_tlv_pad
3. is_valid_tlv_boundary
4. add_tlv
5. delete_tlv
6. has_egr_tlv
7. SEC
8. SEC
9. SEC
10. SEC

   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_helpers.h"
   7 #include "bpf_endian.h"
   8 
   9 /* Packet parsing state machine helpers. */
  10 #define cursor_advance(_cursor, _len) \
  11         ({ void *_tmp = _cursor; _cursor += _len; _tmp; })
  12 
  13 #define SR6_FLAG_ALERT (1 << 4)
  14 
  15 #define BPF_PACKET_HEADER __attribute__((packed))
  16 
  17 struct ip6_t {
  18         unsigned int ver:4;
  19         unsigned int priority:8;
  20         unsigned int flow_label:20;
  21         unsigned short payload_len;
  22         unsigned char next_header;
  23         unsigned char hop_limit;
  24         unsigned long long src_hi;
  25         unsigned long long src_lo;
  26         unsigned long long dst_hi;
  27         unsigned long long dst_lo;
  28 } BPF_PACKET_HEADER;
  29 
  30 struct ip6_addr_t {
  31         unsigned long long hi;
  32         unsigned long long lo;
  33 } BPF_PACKET_HEADER;
  34 
  35 struct ip6_srh_t {
  36         unsigned char nexthdr;
  37         unsigned char hdrlen;
  38         unsigned char type;
  39         unsigned char segments_left;
  40         unsigned char first_segment;
  41         unsigned char flags;
  42         unsigned short tag;
  43 
  44         struct ip6_addr_t segments[0];
  45 } BPF_PACKET_HEADER;
  46 
  47 struct sr6_tlv_t {
  48         unsigned char type;
  49         unsigned char len;
  50         unsigned char value[0];
  51 } BPF_PACKET_HEADER;
  52 
  53 static __always_inline struct ip6_srh_t *get_srh(struct __sk_buff *skb)
  54 {
  55         void *cursor, *data_end;
  56         struct ip6_srh_t *srh;
  57         struct ip6_t *ip;
  58         uint8_t *ipver;
  59 
  60         data_end = (void *)(long)skb->data_end;
  61         cursor = (void *)(long)skb->data;
  62         ipver = (uint8_t *)cursor;
  63 
  64         if ((void *)ipver + sizeof(*ipver) > data_end)
  65                 return NULL;
  66 
  67         if ((*ipver >> 4) != 6)
  68                 return NULL;
  69 
  70         ip = cursor_advance(cursor, sizeof(*ip));
  71         if ((void *)ip + sizeof(*ip) > data_end)
  72                 return NULL;
  73 
  74         if (ip->next_header != 43)
  75                 return NULL;
  76 
  77         srh = cursor_advance(cursor, sizeof(*srh));
  78         if ((void *)srh + sizeof(*srh) > data_end)
  79                 return NULL;
  80 
  81         if (srh->type != 4)
  82                 return NULL;
  83 
  84         return srh;
  85 }
  86 
  87 static __always_inline
  88 int update_tlv_pad(struct __sk_buff *skb, uint32_t new_pad,
  89                    uint32_t old_pad, uint32_t pad_off)
  90 {
  91         int err;
  92 
  93         if (new_pad != old_pad) {
  94                 err = bpf_lwt_seg6_adjust_srh(skb, pad_off,
  95                                           (int) new_pad - (int) old_pad);
  96                 if (err)
  97                         return err;
  98         }
  99 
 100         if (new_pad > 0) {
 101                 char pad_tlv_buf[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 102                                         0, 0, 0};
 103                 struct sr6_tlv_t *pad_tlv = (struct sr6_tlv_t *) pad_tlv_buf;
 104 
 105                 pad_tlv->type = SR6_TLV_PADDING;
 106                 pad_tlv->len = new_pad - 2;
 107 
 108                 err = bpf_lwt_seg6_store_bytes(skb, pad_off,
 109                                                (void *)pad_tlv_buf, new_pad);
 110                 if (err)
 111                         return err;
 112         }
 113 
 114         return 0;
 115 }
 116 
 117 static __always_inline
 118 int is_valid_tlv_boundary(struct __sk_buff *skb, struct ip6_srh_t *srh,
 119                           uint32_t *tlv_off, uint32_t *pad_size,
 120                           uint32_t *pad_off)
 121 {
 122         uint32_t srh_off, cur_off;
 123         int offset_valid = 0;
 124         int err;
 125 
 126         srh_off = (char *)srh - (char *)(long)skb->data;
 127         // cur_off = end of segments, start of possible TLVs
 128         cur_off = srh_off + sizeof(*srh) +
 129                 sizeof(struct ip6_addr_t) * (srh->first_segment + 1);
 130 
 131         *pad_off = 0;
 132 
 133         // we can only go as far as ~10 TLVs due to the BPF max stack size
 134         #pragma clang loop unroll(full)
 135         for (int i = 0; i < 10; i++) {
 136                 struct sr6_tlv_t tlv;
 137 
 138                 if (cur_off == *tlv_off)
 139                         offset_valid = 1;
 140 
 141                 if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3))
 142                         break;
 143 
 144                 err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv));
 145                 if (err)
 146                         return err;
 147 
 148                 if (tlv.type == SR6_TLV_PADDING) {
 149                         *pad_size = tlv.len + sizeof(tlv);
 150                         *pad_off = cur_off;
 151 
 152                         if (*tlv_off == srh_off) {
 153                                 *tlv_off = cur_off;
 154                                 offset_valid = 1;
 155                         }
 156                         break;
 157 
 158                 } else if (tlv.type == SR6_TLV_HMAC) {
 159                         break;
 160                 }
 161 
 162                 cur_off += sizeof(tlv) + tlv.len;
 163         } // we reached the padding or HMAC TLVs, or the end of the SRH
 164 
 165         if (*pad_off == 0)
 166                 *pad_off = cur_off;
 167 
 168         if (*tlv_off == -1)
 169                 *tlv_off = cur_off;
 170         else if (!offset_valid)
 171                 return -EINVAL;
 172 
 173         return 0;
 174 }
 175 
 176 static __always_inline
 177 int add_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh, uint32_t tlv_off,
 178             struct sr6_tlv_t *itlv, uint8_t tlv_size)
 179 {
 180         uint32_t srh_off = (char *)srh - (char *)(long)skb->data;
 181         uint8_t len_remaining, new_pad;
 182         uint32_t pad_off = 0;
 183         uint32_t pad_size = 0;
 184         uint32_t partial_srh_len;
 185         int err;
 186 
 187         if (tlv_off != -1)
 188                 tlv_off += srh_off;
 189 
 190         if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC)
 191                 return -EINVAL;
 192 
 193         err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
 194         if (err)
 195                 return err;
 196 
 197         err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len);
 198         if (err)
 199                 return err;
 200 
 201         err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size);
 202         if (err)
 203                 return err;
 204 
 205         // the following can't be moved inside update_tlv_pad because the
 206         // bpf verifier has some issues with it
 207         pad_off += sizeof(*itlv) + itlv->len;
 208         partial_srh_len = pad_off - srh_off;
 209         len_remaining = partial_srh_len % 8;
 210         new_pad = 8 - len_remaining;
 211 
 212         if (new_pad == 1) // cannot pad for 1 byte only
 213                 new_pad = 9;
 214         else if (new_pad == 8)
 215                 new_pad = 0;
 216 
 217         return update_tlv_pad(skb, new_pad, pad_size, pad_off);
 218 }
 219 
 220 static __always_inline
 221 int delete_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh,
 222                uint32_t tlv_off)
 223 {
 224         uint32_t srh_off = (char *)srh - (char *)(long)skb->data;
 225         uint8_t len_remaining, new_pad;
 226         uint32_t partial_srh_len;
 227         uint32_t pad_off = 0;
 228         uint32_t pad_size = 0;
 229         struct sr6_tlv_t tlv;
 230         int err;
 231 
 232         tlv_off += srh_off;
 233 
 234         err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
 235         if (err)
 236                 return err;
 237 
 238         err = bpf_skb_load_bytes(skb, tlv_off, &tlv, sizeof(tlv));
 239         if (err)
 240                 return err;
 241 
 242         err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, -(sizeof(tlv) + tlv.len));
 243         if (err)
 244                 return err;
 245 
 246         pad_off -= sizeof(tlv) + tlv.len;
 247         partial_srh_len = pad_off - srh_off;
 248         len_remaining = partial_srh_len % 8;
 249         new_pad = 8 - len_remaining;
 250         if (new_pad == 1) // cannot pad for 1 byte only
 251                 new_pad = 9;
 252         else if (new_pad == 8)
 253                 new_pad = 0;
 254 
 255         return update_tlv_pad(skb, new_pad, pad_size, pad_off);
 256 }
 257 
 258 static __always_inline
 259 int has_egr_tlv(struct __sk_buff *skb, struct ip6_srh_t *srh)
 260 {
 261         int tlv_offset = sizeof(struct ip6_t) + sizeof(struct ip6_srh_t) +
 262                 ((srh->first_segment + 1) << 4);
 263         struct sr6_tlv_t tlv;
 264 
 265         if (bpf_skb_load_bytes(skb, tlv_offset, &tlv, sizeof(struct sr6_tlv_t)))
 266                 return 0;
 267 
 268         if (tlv.type == SR6_TLV_EGRESS && tlv.len == 18) {
 269                 struct ip6_addr_t egr_addr;
 270 
 271                 if (bpf_skb_load_bytes(skb, tlv_offset + 4, &egr_addr, 16))
 272                         return 0;
 273 
 274                 // check if egress TLV value is correct
 275                 if (bpf_be64_to_cpu(egr_addr.hi) == 0xfd00000000000000 &&
 276                     bpf_be64_to_cpu(egr_addr.lo) == 0x4)
 277                         return 1;
 278         }
 279 
 280         return 0;
 281 }
 282 
 283 // This function will push a SRH with segments fd00::1, fd00::2, fd00::3,
 284 // fd00::4
 285 SEC("encap_srh")
 286 int __encap_srh(struct __sk_buff *skb)
 287 {
 288         unsigned long long hi = 0xfd00000000000000;
 289         struct ip6_addr_t *seg;
 290         struct ip6_srh_t *srh;
 291         char srh_buf[72]; // room for 4 segments
 292         int err;
 293 
 294         srh = (struct ip6_srh_t *)srh_buf;
 295         srh->nexthdr = 0;
 296         srh->hdrlen = 8;
 297         srh->type = 4;
 298         srh->segments_left = 3;
 299         srh->first_segment = 3;
 300         srh->flags = 0;
 301         srh->tag = 0;
 302 
 303         seg = (struct ip6_addr_t *)((char *)srh + sizeof(*srh));
 304 
 305         #pragma clang loop unroll(full)
 306         for (unsigned long long lo = 0; lo < 4; lo++) {
 307                 seg->lo = bpf_cpu_to_be64(4 - lo);
 308                 seg->hi = bpf_cpu_to_be64(hi);
 309                 seg = (struct ip6_addr_t *)((char *)seg + sizeof(*seg));
 310         }
 311 
 312         err = bpf_lwt_push_encap(skb, 0, (void *)srh, sizeof(srh_buf));
 313         if (err)
 314                 return BPF_DROP;
 315 
 316         return BPF_REDIRECT;
 317 }
 318 
 319 // Add an Egress TLV fc00::4, add the flag A,
 320 // and apply End.X action to fc42::1
 321 SEC("add_egr_x")
 322 int __add_egr_x(struct __sk_buff *skb)
 323 {
 324         unsigned long long hi = 0xfc42000000000000;
 325         unsigned long long lo = 0x1;
 326         struct ip6_srh_t *srh = get_srh(skb);
 327         uint8_t new_flags = SR6_FLAG_ALERT;
 328         struct ip6_addr_t addr;
 329         int err, offset;
 330 
 331         if (srh == NULL)
 332                 return BPF_DROP;
 333 
 334         uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
 335                            0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4};
 336 
 337         err = add_tlv(skb, srh, (srh->hdrlen+1) << 3,
 338                       (struct sr6_tlv_t *)&tlv, 20);
 339         if (err)
 340                 return BPF_DROP;
 341 
 342         offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
 343         err = bpf_lwt_seg6_store_bytes(skb, offset,
 344                                        (void *)&new_flags, sizeof(new_flags));
 345         if (err)
 346                 return BPF_DROP;
 347 
 348         addr.lo = bpf_cpu_to_be64(lo);
 349         addr.hi = bpf_cpu_to_be64(hi);
 350         err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X,
 351                                   (void *)&addr, sizeof(addr));
 352         if (err)
 353                 return BPF_DROP;
 354         return BPF_REDIRECT;
 355 }
 356 
 357 // Pop the Egress TLV, reset the flags, change the tag 2442 and finally do a
 358 // simple End action
 359 SEC("pop_egr")
 360 int __pop_egr(struct __sk_buff *skb)
 361 {
 362         struct ip6_srh_t *srh = get_srh(skb);
 363         uint16_t new_tag = bpf_htons(2442);
 364         uint8_t new_flags = 0;
 365         int err, offset;
 366 
 367         if (srh == NULL)
 368                 return BPF_DROP;
 369 
 370         if (srh->flags != SR6_FLAG_ALERT)
 371                 return BPF_DROP;
 372 
 373         if (srh->hdrlen != 11) // 4 segments + Egress TLV + Padding TLV
 374                 return BPF_DROP;
 375 
 376         if (!has_egr_tlv(skb, srh))
 377                 return BPF_DROP;
 378 
 379         err = delete_tlv(skb, srh, 8 + (srh->first_segment + 1) * 16);
 380         if (err)
 381                 return BPF_DROP;
 382 
 383         offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
 384         if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_flags,
 385                                      sizeof(new_flags)))
 386                 return BPF_DROP;
 387 
 388         offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, tag);
 389         if (bpf_lwt_seg6_store_bytes(skb, offset, (void *)&new_tag,
 390                                      sizeof(new_tag)))
 391                 return BPF_DROP;
 392 
 393         return BPF_OK;
 394 }
 395 
 396 // Inspect if the Egress TLV and flag have been removed, if the tag is correct,
 397 // then apply a End.T action to reach the last segment
 398 SEC("inspect_t")
 399 int __inspect_t(struct __sk_buff *skb)
 400 {
 401         struct ip6_srh_t *srh = get_srh(skb);
 402         int table = 117;
 403         int err;
 404 
 405         if (srh == NULL)
 406                 return BPF_DROP;
 407 
 408         if (srh->flags != 0)
 409                 return BPF_DROP;
 410 
 411         if (srh->tag != bpf_htons(2442))
 412                 return BPF_DROP;
 413 
 414         if (srh->hdrlen != 8) // 4 segments
 415                 return BPF_DROP;
 416 
 417         err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_T,
 418                                   (void *)&table, sizeof(table));
 419 
 420         if (err)
 421                 return BPF_DROP;
 422 
 423         return BPF_REDIRECT;
 424 }
 425 
 426 char __license[] SEC("license") = "GPL";