1 /*- 2 * Copyright 1996-1998 John D. Polstra. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 * 25 * $FreeBSD$ 26 */ 27 28 #include <sys/param.h> 29 #include <sys/mman.h> 30 #include <sys/stat.h> 31 32 #include <errno.h> 33 #include <stddef.h> 34 #include <stdlib.h> 35 #include <string.h> 36 #include <unistd.h> 37 38 #include "debug.h" 39 #include "rtld.h" 40 41 static Elf_Ehdr *get_elf_header (int, const char *); 42 static int convert_prot(int); /* Elf flags -> mmap protection */ 43 static int convert_flags(int); /* Elf flags -> mmap flags */ 44 45 /* 46 * Map a shared object into memory. The "fd" argument is a file descriptor, 47 * which must be open on the object and positioned at its beginning. 48 * The "path" argument is a pathname that is used only for error messages. 49 * 50 * The return value is a pointer to a newly-allocated Obj_Entry structure 51 * for the shared object. Returns NULL on failure. 52 */ 53 Obj_Entry * 54 map_object(int fd, const char *path, const struct stat *sb) 55 { 56 Obj_Entry *obj; 57 Elf_Ehdr *hdr; 58 int i; 59 Elf_Phdr *phdr; 60 Elf_Phdr *phlimit; 61 Elf_Phdr **segs; 62 int nsegs; 63 Elf_Phdr *phdyn; 64 Elf_Phdr *phphdr; 65 Elf_Phdr *phinterp; 66 caddr_t mapbase; 67 size_t mapsize; 68 Elf_Off base_offset; 69 Elf_Addr base_vaddr; 70 Elf_Addr base_vlimit; 71 caddr_t base_addr; 72 Elf_Off data_offset; 73 Elf_Addr data_vaddr; 74 Elf_Addr data_vlimit; 75 caddr_t data_addr; 76 int data_prot; 77 int data_flags; 78 Elf_Addr clear_vaddr; 79 caddr_t clear_addr; 80 caddr_t clear_page; 81 size_t nclear; 82 Elf_Addr bss_vaddr; 83 Elf_Addr bss_vlimit; 84 caddr_t bss_addr; 85 86 hdr = get_elf_header(fd, path); 87 if (hdr == NULL) 88 return (NULL); 89 90 /* 91 * Scan the program header entries, and save key information. 92 * 93 * We rely on there being exactly two load segments, text and data, 94 * in that order. 95 */ 96 phdr = (Elf_Phdr *) ((char *)hdr + hdr->e_phoff); 97 phlimit = phdr + hdr->e_phnum; 98 nsegs = -1; 99 phdyn = phphdr = phinterp = NULL; 100 segs = alloca(sizeof(segs[0]) * hdr->e_phnum); 101 while (phdr < phlimit) { 102 switch (phdr->p_type) { 103 104 case PT_INTERP: 105 phinterp = phdr; 106 break; 107 108 case PT_LOAD: 109 segs[++nsegs] = phdr; 110 if (segs[nsegs]->p_align < PAGE_SIZE) { 111 _rtld_error("%s: PT_LOAD segment %d not page-aligned", 112 path, nsegs); 113 return NULL; 114 } 115 break; 116 117 case PT_PHDR: 118 phphdr = phdr; 119 break; 120 121 case PT_DYNAMIC: 122 phdyn = phdr; 123 break; 124 } 125 126 ++phdr; 127 } 128 if (phdyn == NULL) { 129 _rtld_error("%s: object is not dynamically-linked", path); 130 return NULL; 131 } 132 133 if (nsegs < 0) { 134 _rtld_error("%s: too few PT_LOAD segments", path); 135 return NULL; 136 } 137 138 /* 139 * Map the entire address space of the object, to stake out our 140 * contiguous region, and to establish the base address for relocation. 141 */ 142 base_offset = trunc_page(segs[0]->p_offset); 143 base_vaddr = trunc_page(segs[0]->p_vaddr); 144 base_vlimit = round_page(segs[nsegs]->p_vaddr + segs[nsegs]->p_memsz); 145 mapsize = base_vlimit - base_vaddr; 146 base_addr = hdr->e_type == ET_EXEC ? (caddr_t) base_vaddr : NULL; 147 148 mapbase = mmap(base_addr, mapsize, convert_prot(segs[0]->p_flags), 149 convert_flags(segs[0]->p_flags), fd, base_offset); 150 if (mapbase == (caddr_t) -1) { 151 _rtld_error("%s: mmap of entire address space failed: %s", 152 path, strerror(errno)); 153 return NULL; 154 } 155 if (base_addr != NULL && mapbase != base_addr) { 156 _rtld_error("%s: mmap returned wrong address: wanted %p, got %p", 157 path, base_addr, mapbase); 158 munmap(mapbase, mapsize); 159 return NULL; 160 } 161 162 for (i = 0; i <= nsegs; i++) { 163 /* Overlay the segment onto the proper region. */ 164 data_offset = trunc_page(segs[i]->p_offset); 165 data_vaddr = trunc_page(segs[i]->p_vaddr); 166 data_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_filesz); 167 data_addr = mapbase + (data_vaddr - base_vaddr); 168 data_prot = convert_prot(segs[i]->p_flags); 169 data_flags = convert_flags(segs[i]->p_flags) | MAP_FIXED; 170 /* Do not call mmap on the first segment - this is redundant */ 171 if (i && mmap(data_addr, data_vlimit - data_vaddr, data_prot, 172 data_flags, fd, data_offset) == (caddr_t) -1) { 173 _rtld_error("%s: mmap of data failed: %s", path, strerror(errno)); 174 return NULL; 175 } 176 177 /* Clear any BSS in the last page of the segment. */ 178 clear_vaddr = segs[i]->p_vaddr + segs[i]->p_filesz; 179 clear_addr = mapbase + (clear_vaddr - base_vaddr); 180 clear_page = mapbase + (trunc_page(clear_vaddr) - base_vaddr); 181 if ((nclear = data_vlimit - clear_vaddr) > 0) { 182 /* Make sure the end of the segment is writable */ 183 if ((data_prot & PROT_WRITE) == 0 && 184 -1 == mprotect(clear_page, PAGE_SIZE, data_prot|PROT_WRITE)) { 185 _rtld_error("%s: mprotect failed: %s", path, 186 strerror(errno)); 187 return NULL; 188 } 189 190 memset(clear_addr, 0, nclear); 191 192 /* Reset the data protection back */ 193 if ((data_prot & PROT_WRITE) == 0) 194 mprotect(clear_page, PAGE_SIZE, data_prot); 195 } 196 197 /* Overlay the BSS segment onto the proper region. */ 198 bss_vaddr = data_vlimit; 199 bss_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_memsz); 200 bss_addr = mapbase + (bss_vaddr - base_vaddr); 201 if (bss_vlimit > bss_vaddr) { /* There is something to do */ 202 if (mmap(bss_addr, bss_vlimit - bss_vaddr, data_prot, 203 MAP_PRIVATE|MAP_FIXED|MAP_ANON, -1, 0) == (caddr_t) -1) { 204 _rtld_error("%s: mmap of bss failed: %s", path, 205 strerror(errno)); 206 return NULL; 207 } 208 } 209 } 210 211 obj = obj_new(); 212 if (sb != NULL) { 213 obj->dev = sb->st_dev; 214 obj->ino = sb->st_ino; 215 } 216 obj->mapbase = mapbase; 217 obj->mapsize = mapsize; 218 obj->textsize = round_page(segs[0]->p_vaddr + segs[0]->p_memsz) - 219 base_vaddr; 220 obj->vaddrbase = base_vaddr; 221 obj->relocbase = mapbase - base_vaddr; 222 obj->dynamic = (const Elf_Dyn *) (obj->relocbase + phdyn->p_vaddr); 223 if (hdr->e_entry != 0) 224 obj->entry = (caddr_t) (obj->relocbase + hdr->e_entry); 225 if (phphdr != NULL) { 226 obj->phdr = (const Elf_Phdr *) (obj->relocbase + phphdr->p_vaddr); 227 obj->phsize = phphdr->p_memsz; 228 } 229 if (phinterp != NULL) 230 obj->interp = (const char *) (obj->relocbase + phinterp->p_vaddr); 231 232 return obj; 233 } 234 235 static Elf_Ehdr * 236 get_elf_header (int fd, const char *path) 237 { 238 static union { 239 Elf_Ehdr hdr; 240 char buf[PAGE_SIZE]; 241 } u; 242 ssize_t nbytes; 243 244 if ((nbytes = read(fd, u.buf, PAGE_SIZE)) == -1) { 245 _rtld_error("%s: read error: %s", path, strerror(errno)); 246 return NULL; 247 } 248 249 /* Make sure the file is valid */ 250 if (nbytes < (ssize_t)sizeof(Elf_Ehdr) || !IS_ELF(u.hdr)) { 251 _rtld_error("%s: invalid file format", path); 252 return NULL; 253 } 254 if (u.hdr.e_ident[EI_CLASS] != ELF_TARG_CLASS 255 || u.hdr.e_ident[EI_DATA] != ELF_TARG_DATA) { 256 _rtld_error("%s: unsupported file layout", path); 257 return NULL; 258 } 259 if (u.hdr.e_ident[EI_VERSION] != EV_CURRENT 260 || u.hdr.e_version != EV_CURRENT) { 261 _rtld_error("%s: unsupported file version", path); 262 return NULL; 263 } 264 if (u.hdr.e_type != ET_EXEC && u.hdr.e_type != ET_DYN) { 265 _rtld_error("%s: unsupported file type", path); 266 return NULL; 267 } 268 if (u.hdr.e_machine != ELF_TARG_MACH) { 269 _rtld_error("%s: unsupported machine", path); 270 return NULL; 271 } 272 273 /* 274 * We rely on the program header being in the first page. This is 275 * not strictly required by the ABI specification, but it seems to 276 * always true in practice. And, it simplifies things considerably. 277 */ 278 if (u.hdr.e_phentsize != sizeof(Elf_Phdr)) { 279 _rtld_error( 280 "%s: invalid shared object: e_phentsize != sizeof(Elf_Phdr)", path); 281 return NULL; 282 } 283 if (u.hdr.e_phoff + u.hdr.e_phnum * sizeof(Elf_Phdr) > (size_t)nbytes) { 284 _rtld_error("%s: program header too large", path); 285 return NULL; 286 } 287 288 return (&u.hdr); 289 } 290 291 void 292 obj_free(Obj_Entry *obj) 293 { 294 Objlist_Entry *elm; 295 296 free(obj->path); 297 while (obj->needed != NULL) { 298 Needed_Entry *needed = obj->needed; 299 obj->needed = needed->next; 300 free(needed); 301 } 302 while (!STAILQ_EMPTY(&obj->dldags)) { 303 elm = STAILQ_FIRST(&obj->dldags); 304 STAILQ_REMOVE_HEAD(&obj->dldags, link); 305 free(elm); 306 } 307 while (!STAILQ_EMPTY(&obj->dagmembers)) { 308 elm = STAILQ_FIRST(&obj->dagmembers); 309 STAILQ_REMOVE_HEAD(&obj->dagmembers, link); 310 free(elm); 311 } 312 free(obj->origin_path); 313 free(obj->priv); 314 free(obj); 315 } 316 317 Obj_Entry * 318 obj_new(void) 319 { 320 Obj_Entry *obj; 321 322 obj = CNEW(Obj_Entry); 323 STAILQ_INIT(&obj->dldags); 324 STAILQ_INIT(&obj->dagmembers); 325 return obj; 326 } 327 328 /* 329 * Given a set of ELF protection flags, return the corresponding protection 330 * flags for MMAP. 331 */ 332 static int 333 convert_prot(int elfflags) 334 { 335 int prot = 0; 336 if (elfflags & PF_R) 337 prot |= PROT_READ; 338 if (elfflags & PF_W) 339 prot |= PROT_WRITE; 340 if (elfflags & PF_X) 341 prot |= PROT_EXEC; 342 return prot; 343 } 344 345 static int 346 convert_flags(int elfflags) 347 { 348 int flags = MAP_PRIVATE; /* All mappings are private */ 349 350 /* 351 * Readonly mappings are marked "MAP_NOCORE", because they can be 352 * reconstructed by a debugger. 353 */ 354 if (!(elfflags & PF_W)) 355 flags |= MAP_NOCORE; 356 return flags; 357 } 358