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 int convert_prot(int); /* Elf flags -> mmap protection */ 42 static int convert_flags(int); /* Elf flags -> mmap flags */ 43 44 /* 45 * Map a shared object into memory. The "fd" argument is a file descriptor, 46 * which must be open on the object and positioned at its beginning. 47 * The "path" argument is a pathname that is used only for error messages. 48 * 49 * The return value is a pointer to a newly-allocated Obj_Entry structure 50 * for the shared object. Returns NULL on failure. 51 */ 52 Obj_Entry * 53 map_object(int fd, const char *path, const struct stat *sb) 54 { 55 Obj_Entry *obj; 56 union { 57 Elf_Ehdr hdr; 58 char buf[PAGE_SIZE]; 59 } u; 60 int i; 61 ssize_t nbytes; 62 Elf_Phdr *phdr; 63 Elf_Phdr *phlimit; 64 Elf_Phdr **segs; 65 int nsegs; 66 Elf_Phdr *phdyn; 67 Elf_Phdr *phphdr; 68 Elf_Phdr *phinterp; 69 caddr_t mapbase; 70 size_t mapsize; 71 Elf_Off base_offset; 72 Elf_Addr base_vaddr; 73 Elf_Addr base_vlimit; 74 caddr_t base_addr; 75 Elf_Off data_offset; 76 Elf_Addr data_vaddr; 77 Elf_Addr data_vlimit; 78 caddr_t data_addr; 79 int data_prot; 80 int data_flags; 81 Elf_Addr clear_vaddr; 82 caddr_t clear_addr; 83 caddr_t clear_page; 84 size_t nclear; 85 Elf_Addr bss_vaddr; 86 Elf_Addr bss_vlimit; 87 caddr_t bss_addr; 88 89 if ((nbytes = read(fd, u.buf, PAGE_SIZE)) == -1) { 90 _rtld_error("%s: read error: %s", path, strerror(errno)); 91 return NULL; 92 } 93 94 /* Make sure the file is valid */ 95 if (nbytes < (ssize_t)sizeof(Elf_Ehdr) 96 || u.hdr.e_ident[EI_MAG0] != ELFMAG0 97 || u.hdr.e_ident[EI_MAG1] != ELFMAG1 98 || u.hdr.e_ident[EI_MAG2] != ELFMAG2 99 || u.hdr.e_ident[EI_MAG3] != ELFMAG3) { 100 _rtld_error("%s: invalid file format", path); 101 return NULL; 102 } 103 if (u.hdr.e_ident[EI_CLASS] != ELF_TARG_CLASS 104 || u.hdr.e_ident[EI_DATA] != ELF_TARG_DATA) { 105 _rtld_error("%s: unsupported file layout", path); 106 return NULL; 107 } 108 if (u.hdr.e_ident[EI_VERSION] != EV_CURRENT 109 || u.hdr.e_version != EV_CURRENT) { 110 _rtld_error("%s: unsupported file version", path); 111 return NULL; 112 } 113 if (u.hdr.e_type != ET_EXEC && u.hdr.e_type != ET_DYN) { 114 _rtld_error("%s: unsupported file type", path); 115 return NULL; 116 } 117 if (u.hdr.e_machine != ELF_TARG_MACH) { 118 _rtld_error("%s: unsupported machine", path); 119 return NULL; 120 } 121 122 /* 123 * We rely on the program header being in the first page. This is 124 * not strictly required by the ABI specification, but it seems to 125 * always true in practice. And, it simplifies things considerably. 126 */ 127 if (u.hdr.e_phentsize != sizeof(Elf_Phdr)) { 128 _rtld_error( 129 "%s: invalid shared object: e_phentsize != sizeof(Elf_Phdr)", path); 130 return NULL; 131 } 132 if (u.hdr.e_phoff + u.hdr.e_phnum * sizeof(Elf_Phdr) > (size_t)nbytes) { 133 _rtld_error("%s: program header too large", path); 134 return NULL; 135 } 136 137 /* 138 * Scan the program header entries, and save key information. 139 * 140 * We rely on there being exactly two load segments, text and data, 141 * in that order. 142 */ 143 phdr = (Elf_Phdr *) (u.buf + u.hdr.e_phoff); 144 phlimit = phdr + u.hdr.e_phnum; 145 nsegs = -1; 146 phdyn = phphdr = phinterp = NULL; 147 segs = alloca(sizeof(segs[0]) * u.hdr.e_phnum); 148 while (phdr < phlimit) { 149 switch (phdr->p_type) { 150 151 case PT_INTERP: 152 phinterp = phdr; 153 break; 154 155 case PT_LOAD: 156 segs[++nsegs] = phdr; 157 if (segs[nsegs]->p_align < PAGE_SIZE) { 158 _rtld_error("%s: PT_LOAD segment %d not page-aligned", 159 path, nsegs); 160 return NULL; 161 } 162 break; 163 164 case PT_PHDR: 165 phphdr = phdr; 166 break; 167 168 case PT_DYNAMIC: 169 phdyn = phdr; 170 break; 171 } 172 173 ++phdr; 174 } 175 if (phdyn == NULL) { 176 _rtld_error("%s: object is not dynamically-linked", path); 177 return NULL; 178 } 179 180 if (nsegs < 0) { 181 _rtld_error("%s: too few PT_LOAD segments", path); 182 return NULL; 183 } 184 185 /* 186 * Map the entire address space of the object, to stake out our 187 * contiguous region, and to establish the base address for relocation. 188 */ 189 base_offset = trunc_page(segs[0]->p_offset); 190 base_vaddr = trunc_page(segs[0]->p_vaddr); 191 base_vlimit = round_page(segs[nsegs]->p_vaddr + segs[nsegs]->p_memsz); 192 mapsize = base_vlimit - base_vaddr; 193 base_addr = u.hdr.e_type == ET_EXEC ? (caddr_t) base_vaddr : NULL; 194 195 mapbase = mmap(base_addr, mapsize, convert_prot(segs[0]->p_flags), 196 convert_flags(segs[0]->p_flags), fd, base_offset); 197 if (mapbase == (caddr_t) -1) { 198 _rtld_error("%s: mmap of entire address space failed: %s", 199 path, strerror(errno)); 200 return NULL; 201 } 202 if (base_addr != NULL && mapbase != base_addr) { 203 _rtld_error("%s: mmap returned wrong address: wanted %p, got %p", 204 path, base_addr, mapbase); 205 munmap(mapbase, mapsize); 206 return NULL; 207 } 208 209 for (i = 0; i <= nsegs; i++) { 210 /* Overlay the segment onto the proper region. */ 211 data_offset = trunc_page(segs[i]->p_offset); 212 data_vaddr = trunc_page(segs[i]->p_vaddr); 213 data_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_filesz); 214 data_addr = mapbase + (data_vaddr - base_vaddr); 215 data_prot = convert_prot(segs[i]->p_flags); 216 data_flags = convert_flags(segs[i]->p_flags) | MAP_FIXED; 217 /* Do not call mmap on the first segment - this is redundant */ 218 if (i && mmap(data_addr, data_vlimit - data_vaddr, data_prot, 219 data_flags, fd, data_offset) == (caddr_t) -1) { 220 _rtld_error("%s: mmap of data failed: %s", path, strerror(errno)); 221 return NULL; 222 } 223 224 /* Clear any BSS in the last page of the segment. */ 225 clear_vaddr = segs[i]->p_vaddr + segs[i]->p_filesz; 226 clear_addr = mapbase + (clear_vaddr - base_vaddr); 227 clear_page = mapbase + (trunc_page(clear_vaddr) - base_vaddr); 228 if ((nclear = data_vlimit - clear_vaddr) > 0) { 229 /* Make sure the end of the segment is writable */ 230 if ((data_prot & PROT_WRITE) == 0 && 231 -1 == mprotect(clear_page, PAGE_SIZE, data_prot|PROT_WRITE)) { 232 _rtld_error("%s: mprotect failed: %s", path, 233 strerror(errno)); 234 return NULL; 235 } 236 237 memset(clear_addr, 0, nclear); 238 239 /* Reset the data protection back */ 240 if ((data_prot & PROT_WRITE) == 0) 241 mprotect(clear_page, PAGE_SIZE, data_prot); 242 } 243 244 /* Overlay the BSS segment onto the proper region. */ 245 bss_vaddr = data_vlimit; 246 bss_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_memsz); 247 bss_addr = mapbase + (bss_vaddr - base_vaddr); 248 if (bss_vlimit > bss_vaddr) { /* There is something to do */ 249 if (mmap(bss_addr, bss_vlimit - bss_vaddr, data_prot, 250 MAP_PRIVATE|MAP_FIXED|MAP_ANON, -1, 0) == (caddr_t) -1) { 251 _rtld_error("%s: mmap of bss failed: %s", path, 252 strerror(errno)); 253 return NULL; 254 } 255 } 256 } 257 258 obj = obj_new(); 259 if (sb != NULL) { 260 obj->dev = sb->st_dev; 261 obj->ino = sb->st_ino; 262 } 263 obj->mapbase = mapbase; 264 obj->mapsize = mapsize; 265 obj->textsize = round_page(segs[0]->p_vaddr + segs[0]->p_memsz) - 266 base_vaddr; 267 obj->vaddrbase = base_vaddr; 268 obj->relocbase = mapbase - base_vaddr; 269 obj->dynamic = (const Elf_Dyn *) (obj->relocbase + phdyn->p_vaddr); 270 if (u.hdr.e_entry != 0) 271 obj->entry = (caddr_t) (obj->relocbase + u.hdr.e_entry); 272 if (phphdr != NULL) { 273 obj->phdr = (const Elf_Phdr *) (obj->relocbase + phphdr->p_vaddr); 274 obj->phsize = phphdr->p_memsz; 275 } 276 if (phinterp != NULL) 277 obj->interp = (const char *) (obj->relocbase + phinterp->p_vaddr); 278 279 return obj; 280 } 281 282 void 283 obj_free(Obj_Entry *obj) 284 { 285 Objlist_Entry *elm; 286 287 free(obj->path); 288 while (obj->needed != NULL) { 289 Needed_Entry *needed = obj->needed; 290 obj->needed = needed->next; 291 free(needed); 292 } 293 while (!STAILQ_EMPTY(&obj->dldags)) { 294 elm = STAILQ_FIRST(&obj->dldags); 295 STAILQ_REMOVE_HEAD(&obj->dldags, link); 296 free(elm); 297 } 298 while (!STAILQ_EMPTY(&obj->dagmembers)) { 299 elm = STAILQ_FIRST(&obj->dagmembers); 300 STAILQ_REMOVE_HEAD(&obj->dagmembers, link); 301 free(elm); 302 } 303 free(obj->priv); 304 free(obj); 305 } 306 307 Obj_Entry * 308 obj_new(void) 309 { 310 Obj_Entry *obj; 311 312 obj = CNEW(Obj_Entry); 313 STAILQ_INIT(&obj->dldags); 314 STAILQ_INIT(&obj->dagmembers); 315 return obj; 316 } 317 318 /* 319 * Given a set of ELF protection flags, return the corresponding protection 320 * flags for MMAP. 321 */ 322 static int 323 convert_prot(int elfflags) 324 { 325 int prot = 0; 326 if (elfflags & PF_R) 327 prot |= PROT_READ; 328 if (elfflags & PF_W) 329 prot |= PROT_WRITE; 330 if (elfflags & PF_X) 331 prot |= PROT_EXEC; 332 return prot; 333 } 334 335 static int 336 convert_flags(int elfflags) 337 { 338 int flags = MAP_PRIVATE; /* All mappings are private */ 339 340 /* 341 * Readonly mappings are marked "MAP_NOCORE", because they can be 342 * reconstructed by a debugger. 343 */ 344 if (!(elfflags & PF_W)) 345 flags |= MAP_NOCORE; 346 return flags; 347 } 348