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 #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";