samples/bpf/bpf_load.c

   1 #include <stdio.h>
   2 #include <sys/types.h>
   3 #include <sys/stat.h>
   4 #include <fcntl.h>
   5 #include <libelf.h>
   6 #include <gelf.h>
   7 #include <errno.h>
   8 #include <unistd.h>
   9 #include <string.h>
  10 #include <stdbool.h>
  11 #include <linux/bpf.h>
  12 #include <linux/filter.h>
  13 #include "libbpf.h"
  14 #include "bpf_helpers.h"
  15 #include "bpf_load.h"
  16
  17 static char license[128];
  18 static bool processed_sec[128];
  19 int map_fd[MAX_MAPS];
  20 int prog_fd[MAX_PROGS];
  21 int prog_cnt;
  22
  23 static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
  24 {
  25         int fd;
  26         bool is_socket = strncmp(event, "socket", 6) == 0;
  27
  28         if (!is_socket)
  29                 /* tracing events tbd */
  30                 return -1;
  31
  32         fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER,
  33                            prog, size, license);
  34
  35         if (fd < 0) {
  36                 printf("bpf_prog_load() err=%d\n%s", errno, bpf_log_buf);
  37                 return -1;
  38         }
  39
  40         prog_fd[prog_cnt++] = fd;
  41
  42         return 0;
  43 }
  44
  45 static int load_maps(struct bpf_map_def *maps, int len)
  46 {
  47         int i;
  48
  49         for (i = 0; i < len / sizeof(struct bpf_map_def); i++) {
  50
  51                 map_fd[i] = bpf_create_map(maps[i].type,
  52                                            maps[i].key_size,
  53                                            maps[i].value_size,
  54                                            maps[i].max_entries);
  55                 if (map_fd[i] < 0)
  56                         return 1;
  57         }
  58         return 0;
  59 }
  60
  61 static int get_sec(Elf *elf, int i, GElf_Ehdr *ehdr, char **shname,
  62                    GElf_Shdr *shdr, Elf_Data **data)
  63 {
  64         Elf_Scn *scn;
  65
  66         scn = elf_getscn(elf, i);
  67         if (!scn)
  68                 return 1;
  69
  70         if (gelf_getshdr(scn, shdr) != shdr)
  71                 return 2;
  72
  73         *shname = elf_strptr(elf, ehdr->e_shstrndx, shdr->sh_name);
  74         if (!*shname || !shdr->sh_size)
  75                 return 3;
  76
  77         *data = elf_getdata(scn, 0);
  78         if (!*data || elf_getdata(scn, *data) != NULL)
  79                 return 4;
  80
  81         return 0;
  82 }
  83
  84 static int parse_relo_and_apply(Elf_Data *data, Elf_Data *symbols,
  85                                 GElf_Shdr *shdr, struct bpf_insn *insn)
  86 {
  87         int i, nrels;
  88
  89         nrels = shdr->sh_size / shdr->sh_entsize;
  90
  91         for (i = 0; i < nrels; i++) {
  92                 GElf_Sym sym;
  93                 GElf_Rel rel;
  94                 unsigned int insn_idx;
  95
  96                 gelf_getrel(data, i, &rel);
  97
  98                 insn_idx = rel.r_offset / sizeof(struct bpf_insn);
  99
 100                 gelf_getsym(symbols, GELF_R_SYM(rel.r_info), &sym);
 101
 102                 if (insn[insn_idx].code != (BPF_LD | BPF_IMM | BPF_DW)) {
 103                         printf("invalid relo for insn[%d].code 0x%x\n",
 104                                insn_idx, insn[insn_idx].code);
 105                         return 1;
 106                 }
 107                 insn[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
 108                 insn[insn_idx].imm = map_fd[sym.st_value / sizeof(struct bpf_map_def)];
 109         }
 110
 111         return 0;
 112 }
 113
 114 int load_bpf_file(char *path)
 115 {
 116         int fd, i;
 117         Elf *elf;
 118         GElf_Ehdr ehdr;
 119         GElf_Shdr shdr, shdr_prog;
 120         Elf_Data *data, *data_prog, *symbols = NULL;
 121         char *shname, *shname_prog;
 122
 123         if (elf_version(EV_CURRENT) == EV_NONE)
 124                 return 1;
 125
 126         fd = open(path, O_RDONLY, 0);
 127         if (fd < 0)
 128                 return 1;
 129
 130         elf = elf_begin(fd, ELF_C_READ, NULL);
 131
 132         if (!elf)
 133                 return 1;
 134
 135         if (gelf_getehdr(elf, &ehdr) != &ehdr)
 136                 return 1;
 137
 138         /* scan over all elf sections to get license and map info */
 139         for (i = 1; i < ehdr.e_shnum; i++) {
 140
 141                 if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
 142                         continue;
 143
 144                 if (0) /* helpful for llvm debugging */
 145                         printf("section %d:%s data %p size %zd link %d flags %d\n",
 146                                i, shname, data->d_buf, data->d_size,
 147                                shdr.sh_link, (int) shdr.sh_flags);
 148
 149                 if (strcmp(shname, "license") == 0) {
 150                         processed_sec[i] = true;
 151                         memcpy(license, data->d_buf, data->d_size);
 152                 } else if (strcmp(shname, "maps") == 0) {
 153                         processed_sec[i] = true;
 154                         if (load_maps(data->d_buf, data->d_size))
 155                                 return 1;
 156                 } else if (shdr.sh_type == SHT_SYMTAB) {
 157                         symbols = data;
 158                 }
 159         }
 160
 161         /* load programs that need map fixup (relocations) */
 162         for (i = 1; i < ehdr.e_shnum; i++) {
 163
 164                 if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
 165                         continue;
 166                 if (shdr.sh_type == SHT_REL) {
 167                         struct bpf_insn *insns;
 168
 169                         if (get_sec(elf, shdr.sh_info, &ehdr, &shname_prog,
 170                                     &shdr_prog, &data_prog))
 171                                 continue;
 172
 173                         insns = (struct bpf_insn *) data_prog->d_buf;
 174
 175                         processed_sec[shdr.sh_info] = true;
 176                         processed_sec[i] = true;
 177
 178                         if (parse_relo_and_apply(data, symbols, &shdr, insns))
 179                                 continue;
 180
 181                         if (memcmp(shname_prog, "events/", 7) == 0 ||
 182                             memcmp(shname_prog, "socket", 6) == 0)
 183                                 load_and_attach(shname_prog, insns, data_prog->d_size);
 184                 }
 185         }
 186
 187         /* load programs that don't use maps */
 188         for (i = 1; i < ehdr.e_shnum; i++) {
 189
 190                 if (processed_sec[i])
 191                         continue;
 192
 193                 if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
 194                         continue;
 195
 196                 if (memcmp(shname, "events/", 7) == 0 ||
 197                     memcmp(shname, "socket", 6) == 0)
 198                         load_and_attach(shname, data->d_buf, data->d_size);
 199         }
 200
 201         close(fd);
 202         return 0;
 203 }