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| | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
| | 2 | /* |
| | 3 | * Compute "sympos", the position used by livepatch to disambiguate |
| | 4 | * duplicate symbol names in the patched object. |
| | 5 | */ |
| | 6 | #include <stdlib.h> |
| | 7 | #include <string.h> |
| | 8 | #include <fcntl.h> |
| | 9 | |
| | 10 | #include <objtool/objtool.h> |
| | 11 | #include <objtool/warn.h> |
| | 12 | #include <objtool/endianness.h> |
| | 13 | #include <objtool/klp.h> |
| | 14 | |
| | 15 | #include <linux/string.h> |
| | 16 | |
| | 17 | struct vmlinux_sym { |
| | 18 | struct hlist_node hash; |
| | 19 | const char *name; |
| | 20 | u64 addr; |
| | 21 | }; |
| | 22 | |
| | 23 | struct vmlinux_symid { |
| | 24 | struct hlist_node hash; |
| | 25 | u64 id; |
| | 26 | u64 addr; |
| | 27 | }; |
| | 28 | |
| | 29 | struct vmlinux_o_symid { |
| | 30 | struct hlist_node hash; |
| | 31 | u64 id; |
| | 32 | unsigned int sym_idx; |
| | 33 | }; |
| | 34 | |
| | 35 | static DEFINE_HASHTABLE(vmlinux_o_symids, 16); |
| | 36 | |
| | 37 | /* |
| | 38 | * The original linked kernel, found next to the orig vmlinux.o. Read with raw |
| | 39 | * libelf rather than elf_open_read(): only the symbol table and the resolved |
| | 40 | * .klp.symid table are needed, not the (huge) instruction/reloc machinery. |
| | 41 | * |
| | 42 | * Both tables are built once by read_orig_vmlinux(). The Elf handle stays |
| | 43 | * open because the hashed names point into its mmapped string table. |
| | 44 | */ |
| | 45 | static struct { |
| | 46 | Elf *elf; |
| | 47 | DECLARE_HASHTABLE(syms, 16); /* name -> address */ |
| | 48 | DECLARE_HASHTABLE(symids, 16); /* .klp.symid id -> address */ |
| | 49 | } vmlinux; |
| | 50 | |
| | 51 | /* |
| | 52 | * Would the symbol be visible to the runtime's kallsyms-based symbol lookup? |
| | 53 | */ |
| | 54 | static bool vmlinux_sym_in_kallsyms(Elf *elf, GElf_Sym *sym) |
| | 55 | { |
| | 56 | unsigned int type = GELF_ST_TYPE(sym->st_info); |
| | 57 | GElf_Shdr shdr; |
| | 58 | Elf_Scn *scn; |
| | 59 | |
| | 60 | if (sym->st_shndx == SHN_UNDEF || sym->st_shndx >= SHN_LORESERVE) |
| | 61 | return false; |
| | 62 | |
| | 63 | if (type == STT_SECTION || type == STT_FILE) |
| | 64 | return false; |
| | 65 | |
| | 66 | scn = elf_getscn(elf, sym->st_shndx); |
| | 67 | if (!scn || !gelf_getshdr(scn, &shdr)) |
| | 68 | return false; |
| | 69 | |
| | 70 | return shdr.sh_flags & SHF_ALLOC; |
| | 71 | } |
| | 72 | |
| | 73 | static int read_orig_vmlinux(const char *filename) |
| | 74 | { |
| | 75 | size_t shstrndx, nr_syms = 0, nr_symids = 0, strtab_idx = 0; |
| | 76 | Elf_Data *symtab_data = NULL, *symid_data = NULL; |
| | 77 | struct klp_symid *symids; |
| | 78 | Elf_Scn *scn = NULL; |
| | 79 | GElf_Ehdr ehdr; |
| | 80 | int fd; |
| | 81 | |
| | 82 | fd = open(filename, O_RDONLY); |
| | 83 | if (fd == -1) { |
| | 84 | ERROR_GLIBC("can't open '%s'", filename); |
| | 85 | return -1; |
| | 86 | } |
| | 87 | |
| | 88 | if (elf_version(EV_CURRENT) == EV_NONE) { |
| | 89 | ERROR_ELF("elf_version"); |
| | 90 | return -1; |
| | 91 | } |
| | 92 | |
| | 93 | vmlinux.elf = elf_begin(fd, ELF_C_READ_MMAP, NULL); |
| | 94 | if (!vmlinux.elf) { |
| | 95 | ERROR_ELF("elf_begin"); |
| | 96 | return -1; |
| | 97 | } |
| | 98 | |
| | 99 | if (!gelf_getehdr(vmlinux.elf, &ehdr)) { |
| | 100 | ERROR_ELF("gelf_getehdr"); |
| | 101 | return -1; |
| | 102 | } |
| | 103 | |
| | 104 | if (elf_getshdrstrndx(vmlinux.elf, &shstrndx)) { |
| | 105 | ERROR_ELF("elf_getshdrstrndx"); |
| | 106 | return -1; |
| | 107 | } |
| | 108 | |
| | 109 | while ((scn = elf_nextscn(vmlinux.elf, scn))) { |
| | 110 | const char *name; |
| | 111 | GElf_Shdr shdr; |
| | 112 | |
| | 113 | if (!gelf_getshdr(scn, &shdr)) { |
| | 114 | ERROR_ELF("gelf_getshdr"); |
| | 115 | return -1; |
| | 116 | } |
| | 117 | |
| | 118 | if (shdr.sh_type == SHT_SYMTAB) { |
| | 119 | symtab_data = elf_getdata(scn, NULL); |
| | 120 | if (!symtab_data) { |
| | 121 | ERROR_ELF("elf_getdata"); |
| | 122 | return -1; |
| | 123 | } |
| | 124 | nr_syms = shdr.sh_size / shdr.sh_entsize; |
| | 125 | strtab_idx = shdr.sh_link; |
| | 126 | continue; |
| | 127 | } |
| | 128 | |
| | 129 | name = elf_strptr(vmlinux.elf, shstrndx, shdr.sh_name); |
| | 130 | if (name && !strcmp(name, KLP_SYMID_SEC)) { |
| | 131 | if (shdr.sh_size % sizeof(struct klp_symid)) { |
| | 132 | ERROR("%s: %s: struct klp_symid size mismatch", |
| | 133 | filename, KLP_SYMID_SEC); |
| | 134 | return -1; |
| | 135 | } |
| | 136 | symid_data = elf_getdata(scn, NULL); |
| | 137 | if (!symid_data) { |
| | 138 | ERROR_ELF("elf_getdata"); |
| | 139 | return -1; |
| | 140 | } |
| | 141 | nr_symids = shdr.sh_size / sizeof(struct klp_symid); |
| | 142 | } |
| | 143 | } |
| | 144 | |
| | 145 | if (!symtab_data) { |
| | 146 | ERROR("%s: missing symbol table", filename); |
| | 147 | return -1; |
| | 148 | } |
| | 149 | |
| | 150 | if (!symid_data) { |
| | 151 | ERROR("%s: missing %s section, kernel not built with CONFIG_KLP_BUILD?", |
| | 152 | filename, KLP_SYMID_SEC); |
| | 153 | return -1; |
| | 154 | } |
| | 155 | |
| | 156 | for (size_t i = 0; i < nr_syms; i++) { |
| | 157 | struct vmlinux_sym *vsym; |
| | 158 | const char *name; |
| | 159 | GElf_Sym s; |
| | 160 | |
| | 161 | if (!gelf_getsym(symtab_data, i, &s)) { |
| | 162 | ERROR_ELF("gelf_getsym"); |
| | 163 | return -1; |
| | 164 | } |
| | 165 | |
| | 166 | if (!vmlinux_sym_in_kallsyms(vmlinux.elf, &s)) |
| | 167 | continue; |
| | 168 | |
| | 169 | name = elf_strptr(vmlinux.elf, strtab_idx, s.st_name); |
| | 170 | if (!name) |
| | 171 | continue; |
| | 172 | |
| | 173 | vsym = calloc(1, sizeof(*vsym)); |
| | 174 | if (!vsym) { |
| | 175 | ERROR_GLIBC("calloc"); |
| | 176 | return -1; |
| | 177 | } |
| | 178 | |
| | 179 | vsym->name = name; |
| | 180 | vsym->addr = s.st_value; |
| | 181 | hash_add(vmlinux.syms, &vsym->hash, str_hash(name)); |
| | 182 | } |
| | 183 | |
| | 184 | symids = symid_data->d_buf; |
| | 185 | |
| | 186 | for (size_t i = 0; i < nr_symids; i++) { |
| | 187 | struct vmlinux_symid *vsymid; |
| | 188 | |
| | 189 | vsymid = calloc(1, sizeof(*vsymid)); |
| | 190 | if (!vsymid) { |
| | 191 | ERROR_GLIBC("calloc"); |
| | 192 | return -1; |
| | 193 | } |
| | 194 | |
| | 195 | vsymid->id = __bswap_if_needed(&ehdr, symids[i].id); |
| | 196 | vsymid->addr = __bswap_if_needed(&ehdr, symids[i].addr); |
| | 197 | hash_add(vmlinux.symids, &vsymid->hash, vsymid->id); |
| | 198 | } |
| | 199 | |
| | 200 | /* the fd and Elf handle stay open, the hashed names live in the mmap */ |
| | 201 | return 0; |
| | 202 | } |
| | 203 | |
| | 204 | /* |
| | 205 | * Read the orig vmlinux.o's .klp.symid table, an array of entries whose 'addr' |
| | 206 | * fields have relocs to the symbols they describe. |
| | 207 | */ |
| | 208 | static int read_vmlinux_o_symids(struct elf *vmlinux_o) |
| | 209 | { |
| | 210 | struct section *sec; |
| | 211 | |
| | 212 | for_each_sec(vmlinux_o, sec) { |
| | 213 | unsigned long nr; |
| | 214 | |
| | 215 | if (strcmp(sec->name, KLP_SYMID_SEC)) |
| | 216 | continue; |
| | 217 | |
| | 218 | if (sec_size(sec) % sizeof(struct klp_symid)) { |
| | 219 | ERROR("%s: %s: struct klp_symid size mismatch", |
| | 220 | vmlinux_o->name, KLP_SYMID_SEC); |
| | 221 | return -1; |
| | 222 | } |
| | 223 | |
| | 224 | nr = sec_size(sec) / sizeof(struct klp_symid); |
| | 225 | |
| | 226 | for (unsigned long i = 0; i < nr; i++) { |
| | 227 | unsigned long offset = i * sizeof(struct klp_symid); |
| | 228 | struct vmlinux_o_symid *entry; |
| | 229 | struct klp_symid *symid; |
| | 230 | struct reloc *reloc; |
| | 231 | |
| | 232 | entry = calloc(1, sizeof(*entry)); |
| | 233 | if (!entry) { |
| | 234 | ERROR_GLIBC("calloc"); |
| | 235 | return -1; |
| | 236 | } |
| | 237 | |
| | 238 | symid = sec->data->d_buf + offset; |
| | 239 | entry->id = bswap_if_needed(vmlinux_o, symid->id); |
| | 240 | |
| | 241 | reloc = find_reloc_by_dest(vmlinux_o, sec, |
| | 242 | offset + offsetof(struct klp_symid, addr)); |
| | 243 | if (!reloc) { |
| | 244 | ERROR("%s: missing reloc for %s entry", |
| | 245 | vmlinux_o->name, KLP_SYMID_SEC); |
| | 246 | return -1; |
| | 247 | } |
| | 248 | entry->sym_idx = reloc->sym->idx; |
| | 249 | |
| | 250 | hash_add(vmlinux_o_symids, &entry->hash, entry->sym_idx); |
| | 251 | } |
| | 252 | } |
| | 253 | |
| | 254 | return 0; |
| | 255 | } |
| | 256 | |
| | 257 | int klp_sympos_init(struct elf *orig) |
| | 258 | { |
| | 259 | char *filename; |
| | 260 | int ret; |
| | 261 | |
| | 262 | if (!str_ends_with(objname, "vmlinux.o")) |
| | 263 | return 0; |
| | 264 | |
| | 265 | if (read_vmlinux_o_symids(orig)) |
| | 266 | return -1; |
| | 267 | |
| | 268 | filename = strndup(objname, strlen(objname) - 2); |
| | 269 | if (!filename) { |
| | 270 | ERROR_GLIBC("strndup"); |
| | 271 | return -1; |
| | 272 | } |
| | 273 | |
| | 274 | ret = read_orig_vmlinux(filename); |
| | 275 | free(filename); |
| | 276 | |
| | 277 | return ret; |
| | 278 | } |
| | 279 | |
| | 280 | /* Find the symbol's id in the orig vmlinux.o's .klp.symid table */ |
| | 281 | static int find_vmlinux_o_symid(struct symbol *sym, u64 *id) |
| | 282 | { |
| | 283 | struct vmlinux_o_symid *entry; |
| | 284 | |
| | 285 | hash_for_each_possible(vmlinux_o_symids, entry, hash, sym->idx) { |
| | 286 | if (entry->sym_idx == sym->idx) { |
| | 287 | *id = entry->id; |
| | 288 | return 0; |
| | 289 | } |
| | 290 | } |
| | 291 | |
| | 292 | ERROR("no %s entry for symbol %s in orig vmlinux.o", KLP_SYMID_SEC, |
| | 293 | sym->name); |
| | 294 | return -1; |
| | 295 | } |
| | 296 | |
| | 297 | /* Find the symbol's final address in the orig vmlinux's .klp.symid table */ |
| | 298 | static int find_vmlinux_symid_addr(u64 id, u64 *addr) |
| | 299 | { |
| | 300 | struct vmlinux_symid *symid; |
| | 301 | |
| | 302 | hash_for_each_possible(vmlinux.symids, symid, hash, id) { |
| | 303 | if (symid->id == id) { |
| | 304 | *addr = symid->addr; |
| | 305 | return 0; |
| | 306 | } |
| | 307 | } |
| | 308 | |
| | 309 | return -1; |
| | 310 | } |
| | 311 | |
| | 312 | /* |
| | 313 | * Find the sympos of a vmlinux-local symbol by ranking its final address |
| | 314 | * among the duplicately named symbols in the linked orig vmlinux, replicating |
| | 315 | * the order in which kallsyms_on_each_match_symbol() counts them. |
| | 316 | */ |
| | 317 | static unsigned long find_vmlinux_sympos(struct symbol *sym) |
| | 318 | { |
| | 319 | unsigned long nr_matches = 0, sympos = 1; |
| | 320 | u32 key = str_hash(sym->name); |
| | 321 | struct vmlinux_sym *vsym; |
| | 322 | bool found = false; |
| | 323 | u64 id, addr; |
| | 324 | |
| | 325 | hash_for_each_possible(vmlinux.syms, vsym, hash, key) |
| | 326 | if (!strcmp(vsym->name, sym->name)) |
| | 327 | nr_matches++; |
| | 328 | |
| | 329 | if (!nr_matches) { |
| | 330 | ERROR("can't find symbol %s in orig vmlinux", sym->name); |
| | 331 | return ULONG_MAX; |
| | 332 | } |
| | 333 | |
| | 334 | /* |
| | 335 | * Unique symbols don't need disambiguating. They also have no |
| | 336 | * .klp.symid entry, which is only emitted for names duplicated in |
| | 337 | * vmlinux.o, so the lookups below would fail. |
| | 338 | */ |
| | 339 | if (nr_matches == 1) |
| | 340 | return 0; |
| | 341 | |
| | 342 | if (find_vmlinux_o_symid(sym, &id)) |
| | 343 | return ULONG_MAX; |
| | 344 | |
| | 345 | if (find_vmlinux_symid_addr(id, &addr)) { |
| | 346 | ERROR("no %s entry for symbol %s in orig vmlinux", KLP_SYMID_SEC, |
| | 347 | sym->name); |
| | 348 | return ULONG_MAX; |
| | 349 | } |
| | 350 | |
| | 351 | hash_for_each_possible(vmlinux.syms, vsym, hash, key) { |
| | 352 | if (strcmp(vsym->name, sym->name)) |
| | 353 | continue; |
| | 354 | |
| | 355 | if (vsym->addr < addr) |
| | 356 | sympos++; |
| | 357 | else if (vsym->addr == addr) |
| | 358 | found = true; |
| | 359 | } |
| | 360 | |
| | 361 | if (!found) { |
| | 362 | ERROR("%s address mismatch for symbol %s, stale orig vmlinux?", |
| | 363 | KLP_SYMID_SEC, sym->name); |
| | 364 | return ULONG_MAX; |
| | 365 | } |
| | 366 | |
| | 367 | return sympos; |
| | 368 | } |
| | 369 | |
| | 370 | /* |
| | 371 | * "sympos" is used by livepatch to disambiguate duplicate symbol names. |
| | 372 | */ |
| | 373 | unsigned long klp_find_sympos(struct elf *elf, struct symbol *sym) |
| | 374 | { |
| | 375 | unsigned long sympos = 0, nr_matches = 0; |
| | 376 | bool has_dup = false; |
| | 377 | struct symbol *s; |
| | 378 | |
| | 379 | if (sym->bind != STB_LOCAL) |
| | 380 | return 0; |
| | 381 | |
| | 382 | /* |
| | 383 | * vmlinux: the final link reorders symbols relative to vmlinux.o, |
| | 384 | * so the position needs to be derived from the linked orig vmlinux via |
| | 385 | * the .klp.symid table. |
| | 386 | */ |
| | 387 | if (vmlinux.elf) |
| | 388 | return find_vmlinux_sympos(sym); |
| | 389 | |
| | 390 | /* |
| | 391 | * modules: the final .ko preserves symbol table order, so a |
| | 392 | * symtab-order count here matches the runtime count done by |
| | 393 | * module_kallsyms_on_each_symbol(). |
| | 394 | */ |
| | 395 | for_each_sym(elf, s) { |
| | 396 | if (!strcmp(s->name, sym->name)) { |
| | 397 | nr_matches++; |
| | 398 | if (s == sym) |
| | 399 | sympos = nr_matches; |
| | 400 | else |
| | 401 | has_dup = true; |
| | 402 | } |
| | 403 | } |
| | 404 | |
| | 405 | if (!sympos) { |
| | 406 | ERROR("can't find sympos for %s", sym->name); |
| | 407 | return ULONG_MAX; |
| | 408 | } |
| | 409 | |
| | 410 | return has_dup ? sympos : 0; |
| | 411 | } |