libexec/rtld-elf/map_object.c

   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: src/libexec/rtld-elf/map_object.c,v 1.7.2.2 2002/12/28 19:49:41 dillon Exp $
  26  * $DragonFly: src/libexec/rtld-elf/map_object.c,v 1.6 2005/03/22 23:56:36 davidxu Exp $
  27  */
  28
  29 #include <sys/param.h>
  30 #include <sys/mman.h>
  31 #include <sys/stat.h>
  32
  33 #include <errno.h>
  34 #include <stddef.h>
  35 #include <stdlib.h>
  36 #include <string.h>
  37 #include <unistd.h>
  38
  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     Elf_Phdr *phtls;
  67     caddr_t mapbase;
  68     size_t mapsize;
  69     Elf_Off base_offset;
  70     Elf_Addr base_vaddr;
  71     Elf_Addr base_vlimit;
  72     caddr_t base_addr;
  73     Elf_Off data_offset;
  74     Elf_Addr data_vaddr;
  75     Elf_Addr data_vlimit;
  76     caddr_t data_addr;
  77     int data_prot;
  78     int data_flags;
  79     Elf_Addr clear_vaddr;
  80     caddr_t clear_addr;
  81     caddr_t clear_page;
  82     size_t nclear;
  83     Elf_Addr bss_vaddr;
  84     Elf_Addr bss_vlimit;
  85     caddr_t bss_addr;
  86
  87     hdr = get_elf_header(fd, path);
  88     if (hdr == NULL)
  89         return NULL;
  90
  91     /*
  92      * Scan the program header entries, and save key information.
  93      *
  94      * We rely on there being exactly two load segments, text and data,
  95      * in that order.
  96      */
  97     phdr = (Elf_Phdr *) ((char *)hdr + hdr->e_phoff);
  98     phlimit = phdr + hdr->e_phnum;
  99     nsegs = -1;
 100     phdyn = phphdr = phinterp = phtls = NULL;
 101     segs = alloca(sizeof(segs[0]) * hdr->e_phnum);
 102     while (phdr < phlimit) {
 103         switch (phdr->p_type) {
 104
 105         case PT_INTERP:
 106             phinterp = phdr;
 107             break;
 108
 109         case PT_LOAD:
 110             segs[++nsegs] = phdr;
 111             if (segs[nsegs]->p_align < PAGE_SIZE) {
 112                 _rtld_error("%s: PT_LOAD segment %d not page-aligned",
 113                     path, nsegs);
 114                 return NULL;
 115             }
 116             break;
 117
 118         case PT_PHDR:
 119             phphdr = phdr;
 120             break;
 121
 122         case PT_DYNAMIC:
 123             phdyn = phdr;
 124             break;
 125         case PT_TLS:
 126             phtls = phdr;
 127             break;
 128         }
 129
 130         ++phdr;
 131     }
 132     if (phdyn == NULL) {
 133         _rtld_error("%s: object is not dynamically-linked", path);
 134         return NULL;
 135     }
 136
 137     if (nsegs < 0) {
 138         _rtld_error("%s: too few PT_LOAD segments", path);
 139         return NULL;
 140     }
 141
 142     /*
 143      * Map the entire address space of the object, to stake out our
 144      * contiguous region, and to establish the base address for relocation.
 145      */
 146     base_offset = trunc_page(segs[0]->p_offset);
 147     base_vaddr = trunc_page(segs[0]->p_vaddr);
 148     base_vlimit = round_page(segs[nsegs]->p_vaddr + segs[nsegs]->p_memsz);
 149     mapsize = base_vlimit - base_vaddr;
 150     base_addr = hdr->e_type == ET_EXEC ? (caddr_t) base_vaddr : NULL;
 151
 152     mapbase = mmap(base_addr, mapsize, convert_prot(segs[0]->p_flags),
 153       convert_flags(segs[0]->p_flags), fd, base_offset);
 154     if (mapbase == (caddr_t) -1) {
 155         _rtld_error("%s: mmap of entire address space failed: %s",
 156           path, strerror(errno));
 157         return NULL;
 158     }
 159     if (base_addr != NULL && mapbase != base_addr) {
 160         _rtld_error("%s: mmap returned wrong address: wanted %p, got %p",
 161           path, base_addr, mapbase);
 162         munmap(mapbase, mapsize);
 163         return NULL;
 164     }
 165
 166     for (i = 0; i <=  nsegs; i++) {
 167         /* Overlay the segment onto the proper region. */
 168         data_offset = trunc_page(segs[i]->p_offset);
 169         data_vaddr = trunc_page(segs[i]->p_vaddr);
 170         data_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_filesz);
 171         data_addr = mapbase + (data_vaddr - base_vaddr);
 172         data_prot = convert_prot(segs[i]->p_flags);
 173         data_flags = convert_flags(segs[i]->p_flags) | MAP_FIXED;
 174         /* Do not call mmap on the first segment - this is redundant */
 175         if (i && mmap(data_addr, data_vlimit - data_vaddr, data_prot,
 176           data_flags, fd, data_offset) == (caddr_t) -1) {
 177             _rtld_error("%s: mmap of data failed: %s", path, strerror(errno));
 178             return NULL;
 179         }
 180
 181         /* Clear any BSS in the last page of the segment. */
 182         clear_vaddr = segs[i]->p_vaddr + segs[i]->p_filesz;
 183         clear_addr = mapbase + (clear_vaddr - base_vaddr);
 184         clear_page = mapbase + (trunc_page(clear_vaddr) - base_vaddr);
 185         if ((nclear = data_vlimit - clear_vaddr) > 0) {
 186             /* Make sure the end of the segment is writable */
 187             if ((data_prot & PROT_WRITE) == 0) {
 188                 if (mprotect(clear_page, PAGE_SIZE, data_prot|PROT_WRITE) < 0) {
 189                         _rtld_error("%s: mprotect failed: %s", path,
 190                             strerror(errno));
 191                         return NULL;
 192                 }
 193             }
 194
 195             memset(clear_addr, 0, nclear);
 196
 197             /*
 198              * reset the data protection back, enable the segment to be
 199              * coredumped since we modified it.
 200              */
 201             if ((data_prot & PROT_WRITE) == 0) {
 202                 madvise(clear_page, PAGE_SIZE, MADV_CORE);
 203                 mprotect(clear_page, PAGE_SIZE, data_prot);
 204             }
 205         }
 206
 207         /* Overlay the BSS segment onto the proper region. */
 208         bss_vaddr = data_vlimit;
 209         bss_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_memsz);
 210         bss_addr = mapbase +  (bss_vaddr - base_vaddr);
 211         if (bss_vlimit > bss_vaddr) {   /* There is something to do */
 212             if (mmap(bss_addr, bss_vlimit - bss_vaddr, data_prot,
 213                 MAP_PRIVATE|MAP_FIXED|MAP_ANON, -1, 0) == (caddr_t) -1) {
 214                     _rtld_error("%s: mmap of bss failed: %s", path,
 215                         strerror(errno));
 216                 return NULL;
 217             }
 218         }
 219     }
 220
 221     obj = obj_new();
 222     if (sb != NULL) {
 223         obj->dev = sb->st_dev;
 224         obj->ino = sb->st_ino;
 225     }
 226     obj->mapbase = mapbase;
 227     obj->mapsize = mapsize;
 228     obj->textsize = round_page(segs[0]->p_vaddr + segs[0]->p_memsz) -
 229       base_vaddr;
 230     obj->vaddrbase = base_vaddr;
 231     obj->relocbase = mapbase - base_vaddr;
 232     obj->dynamic = (const Elf_Dyn *) (obj->relocbase + phdyn->p_vaddr);
 233     if (hdr->e_entry != 0)
 234         obj->entry = (caddr_t) (obj->relocbase + hdr->e_entry);
 235     if (phphdr != NULL) {
 236         obj->phdr = (const Elf_Phdr *) (obj->relocbase + phphdr->p_vaddr);
 237         obj->phsize = phphdr->p_memsz;
 238     }
 239     if (phinterp != NULL)
 240         obj->interp = (const char *) (obj->relocbase + phinterp->p_vaddr);
 241     if (phtls != NULL) {
 242         tls_dtv_generation++;
 243         obj->tlsindex = ++tls_max_index;
 244         obj->tlssize = phtls->p_memsz;
 245         obj->tlsalign = phtls->p_align;
 246         obj->tlsinitsize = phtls->p_filesz;
 247         obj->tlsinit = mapbase + phtls->p_vaddr;
 248     }
 249     return obj;
 250 }
 251
 252 static Elf_Ehdr *
 253 get_elf_header (int fd, const char *path)
 254 {
 255     static union {
 256         Elf_Ehdr hdr;
 257         char buf[PAGE_SIZE];
 258     } u;
 259     ssize_t nbytes;
 260
 261     if ((nbytes = read(fd, u.buf, PAGE_SIZE)) == -1) {
 262         _rtld_error("%s: read error: %s", path, strerror(errno));
 263         return NULL;
 264     }
 265
 266     /* Make sure the file is valid */
 267     if (nbytes < (ssize_t)sizeof(Elf_Ehdr) || !IS_ELF(u.hdr)) {
 268         _rtld_error("%s: invalid file format", path);
 269         return NULL;
 270     }
 271     if (u.hdr.e_ident[EI_CLASS] != ELF_TARG_CLASS
 272       || u.hdr.e_ident[EI_DATA] != ELF_TARG_DATA) {
 273         _rtld_error("%s: unsupported file layout", path);
 274         return NULL;
 275     }
 276     if (u.hdr.e_ident[EI_VERSION] != EV_CURRENT
 277       || u.hdr.e_version != EV_CURRENT) {
 278         _rtld_error("%s: unsupported file version", path);
 279         return NULL;
 280     }
 281     if (u.hdr.e_type != ET_EXEC && u.hdr.e_type != ET_DYN) {
 282         _rtld_error("%s: unsupported file type", path);
 283         return NULL;
 284     }
 285     if (u.hdr.e_machine != ELF_TARG_MACH) {
 286         _rtld_error("%s: unsupported machine", path);
 287         return NULL;
 288     }
 289
 290     /*
 291      * We rely on the program header being in the first page.  This is
 292      * not strictly required by the ABI specification, but it seems to
 293      * always true in practice.  And, it simplifies things considerably.
 294      */
 295     if (u.hdr.e_phentsize != sizeof(Elf_Phdr)) {
 296         _rtld_error(
 297           "%s: invalid shared object: e_phentsize != sizeof(Elf_Phdr)", path);
 298         return NULL;
 299     }
 300     if (u.hdr.e_phoff + u.hdr.e_phnum * sizeof(Elf_Phdr) > (size_t)nbytes) {
 301         _rtld_error("%s: program header too large", path);
 302         return NULL;
 303     }
 304
 305     return (&u.hdr);
 306 }
 307
 308 void
 309 obj_free(Obj_Entry *obj)
 310 {
 311     Objlist_Entry *elm;
 312
 313     if (obj->tls_done) {
 314         free_tls_offset(obj);
 315     }
 316     free(obj->origin_path);
 317     free(obj->path);
 318     while (obj->needed != NULL) {
 319         Needed_Entry *needed = obj->needed;
 320         obj->needed = needed->next;
 321         free(needed);
 322     }
 323     while (!STAILQ_EMPTY(&obj->dldags)) {
 324         elm = STAILQ_FIRST(&obj->dldags);
 325         STAILQ_REMOVE_HEAD(&obj->dldags, link);
 326         free(elm);
 327     }
 328     while (!STAILQ_EMPTY(&obj->dagmembers)) {
 329         elm = STAILQ_FIRST(&obj->dagmembers);
 330         STAILQ_REMOVE_HEAD(&obj->dagmembers, link);
 331         free(elm);
 332     }
 333     free(obj);
 334 }
 335
 336 Obj_Entry *
 337 obj_new(void)
 338 {
 339     Obj_Entry *obj;
 340
 341     obj = CNEW(Obj_Entry);
 342     STAILQ_INIT(&obj->dldags);
 343     STAILQ_INIT(&obj->dagmembers);
 344     return obj;
 345 }
 346
 347 /*
 348  * Given a set of ELF protection flags, return the corresponding protection
 349  * flags for MMAP.
 350  */
 351 static int
 352 convert_prot(int elfflags)
 353 {
 354     int prot = 0;
 355     if (elfflags & PF_R)
 356         prot |= PROT_READ;
 357     if (elfflags & PF_W)
 358         prot |= PROT_WRITE;
 359     if (elfflags & PF_X)
 360         prot |= PROT_EXEC;
 361     return prot;
 362 }
 363
 364 static int
 365 convert_flags(int elfflags)
 366 {
 367     int flags = MAP_PRIVATE; /* All mappings are private */
 368
 369     /*
 370      * Readonly mappings are marked "MAP_NOCORE", because they can be
 371      * reconstructed by a debugger.
 372      */
 373     if (!(elfflags & PF_W))
 374         flags |= MAP_NOCORE;
 375     return flags;
 376 }