tools/testing/selftests/bpf/progs/test_seg6_loop.c

   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 /* 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 int update_tlv_pad(struct __sk_buff *skb,
  88                                           uint32_t new_pad, uint32_t old_pad,
  89                                           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 int is_valid_tlv_boundary(struct __sk_buff *skb,
 118                                                  struct ip6_srh_t *srh,
 119                                                  uint32_t *tlv_off,
 120                                                  uint32_t *pad_size,
 121                                                  uint32_t *pad_off)
 122 {
 123         uint32_t srh_off, cur_off;
 124         int offset_valid = 0;
 125         int err;
 126
 127         srh_off = (char *)srh - (char *)(long)skb->data;
 128         // cur_off = end of segments, start of possible TLVs
 129         cur_off = srh_off + sizeof(*srh) +
 130                 sizeof(struct ip6_addr_t) * (srh->first_segment + 1);
 131
 132         *pad_off = 0;
 133
 134         // we can only go as far as ~10 TLVs due to the BPF max stack size
 135         // workaround: define induction variable "i" as "long" instead
 136         // of "int" to prevent alu32 sub-register spilling.
 137         #pragma clang loop unroll(disable)
 138         for (long i = 0; i < 100; i++) {
 139                 struct sr6_tlv_t tlv;
 140
 141                 if (cur_off == *tlv_off)
 142                         offset_valid = 1;
 143
 144                 if (cur_off >= srh_off + ((srh->hdrlen + 1) << 3))
 145                         break;
 146
 147                 err = bpf_skb_load_bytes(skb, cur_off, &tlv, sizeof(tlv));
 148                 if (err)
 149                         return err;
 150
 151                 if (tlv.type == SR6_TLV_PADDING) {
 152                         *pad_size = tlv.len + sizeof(tlv);
 153                         *pad_off = cur_off;
 154
 155                         if (*tlv_off == srh_off) {
 156                                 *tlv_off = cur_off;
 157                                 offset_valid = 1;
 158                         }
 159                         break;
 160
 161                 } else if (tlv.type == SR6_TLV_HMAC) {
 162                         break;
 163                 }
 164
 165                 cur_off += sizeof(tlv) + tlv.len;
 166         } // we reached the padding or HMAC TLVs, or the end of the SRH
 167
 168         if (*pad_off == 0)
 169                 *pad_off = cur_off;
 170
 171         if (*tlv_off == -1)
 172                 *tlv_off = cur_off;
 173         else if (!offset_valid)
 174                 return -EINVAL;
 175
 176         return 0;
 177 }
 178
 179 static __always_inline int add_tlv(struct __sk_buff *skb,
 180                                    struct ip6_srh_t *srh, uint32_t tlv_off,
 181                                    struct sr6_tlv_t *itlv, uint8_t tlv_size)
 182 {
 183         uint32_t srh_off = (char *)srh - (char *)(long)skb->data;
 184         uint8_t len_remaining, new_pad;
 185         uint32_t pad_off = 0;
 186         uint32_t pad_size = 0;
 187         uint32_t partial_srh_len;
 188         int err;
 189
 190         if (tlv_off != -1)
 191                 tlv_off += srh_off;
 192
 193         if (itlv->type == SR6_TLV_PADDING || itlv->type == SR6_TLV_HMAC)
 194                 return -EINVAL;
 195
 196         err = is_valid_tlv_boundary(skb, srh, &tlv_off, &pad_size, &pad_off);
 197         if (err)
 198                 return err;
 199
 200         err = bpf_lwt_seg6_adjust_srh(skb, tlv_off, sizeof(*itlv) + itlv->len);
 201         if (err)
 202                 return err;
 203
 204         err = bpf_lwt_seg6_store_bytes(skb, tlv_off, (void *)itlv, tlv_size);
 205         if (err)
 206                 return err;
 207
 208         // the following can't be moved inside update_tlv_pad because the
 209         // bpf verifier has some issues with it
 210         pad_off += sizeof(*itlv) + itlv->len;
 211         partial_srh_len = pad_off - srh_off;
 212         len_remaining = partial_srh_len % 8;
 213         new_pad = 8 - len_remaining;
 214
 215         if (new_pad == 1) // cannot pad for 1 byte only
 216                 new_pad = 9;
 217         else if (new_pad == 8)
 218                 new_pad = 0;
 219
 220         return update_tlv_pad(skb, new_pad, pad_size, pad_off);
 221 }
 222
 223 // Add an Egress TLV fc00::4, add the flag A,
 224 // and apply End.X action to fc42::1
 225 SEC("lwt_seg6local")
 226 int __add_egr_x(struct __sk_buff *skb)
 227 {
 228         unsigned long long hi = 0xfc42000000000000;
 229         unsigned long long lo = 0x1;
 230         struct ip6_srh_t *srh = get_srh(skb);
 231         uint8_t new_flags = SR6_FLAG_ALERT;
 232         struct ip6_addr_t addr;
 233         int err, offset;
 234
 235         if (srh == NULL)
 236                 return BPF_DROP;
 237
 238         uint8_t tlv[20] = {2, 18, 0, 0, 0xfd, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
 239                            0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x4};
 240
 241         err = add_tlv(skb, srh, (srh->hdrlen+1) << 3,
 242                       (struct sr6_tlv_t *)&tlv, 20);
 243         if (err)
 244                 return BPF_DROP;
 245
 246         offset = sizeof(struct ip6_t) + offsetof(struct ip6_srh_t, flags);
 247         err = bpf_lwt_seg6_store_bytes(skb, offset,
 248                                        (void *)&new_flags, sizeof(new_flags));
 249         if (err)
 250                 return BPF_DROP;
 251
 252         addr.lo = bpf_cpu_to_be64(lo);
 253         addr.hi = bpf_cpu_to_be64(hi);
 254         err = bpf_lwt_seg6_action(skb, SEG6_LOCAL_ACTION_END_X,
 255                                   (void *)&addr, sizeof(addr));
 256         if (err)
 257                 return BPF_DROP;
 258         return BPF_REDIRECT;
 259 }
 260 char __license[] SEC("license") = "GPL";