elf/dl-minimal.c

   1 /* Minimal replacements for basic facilities used in the dynamic linker.
   2    Copyright (C) 1995-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <limits.h>
  21 #include <stdio.h>
  22 #include <string.h>
  23 #include <tls.h>
  24 #include <unistd.h>
  25 #include <sys/mman.h>
  26 #include <sys/param.h>
  27 #include <sys/types.h>
  28 #include <ldsodefs.h>
  29 #include <dl-irel.h>
  30 #include <dl-hash.h>
  31 #include <dl-sym-post.h>
  32 #include <_itoa.h>
  33 #include <malloc/malloc-internal.h>
  34
  35 #include <assert.h>
  36
  37 /* The rtld startup code calls __rtld_malloc_init_stubs after the
  38   first self-relocation to adjust the pointers to the minimal
  39   implementation below.  Before the final relocation,
  40   __rtld_malloc_init_real is called to replace the pointers with the
  41   real implementation.  */
  42 __typeof (calloc) *__rtld_calloc attribute_relro;
  43 __typeof (free) *__rtld_free attribute_relro;
  44 __typeof (malloc) *__rtld_malloc attribute_relro;
  45 __typeof (realloc) *__rtld_realloc attribute_relro;
  46
  47 /* Defined below.  */
  48 static __typeof (calloc) rtld_calloc;
  49 static __typeof (free) rtld_free;
  50 static __typeof (malloc) rtld_malloc;
  51 static __typeof (realloc) rtld_realloc;
  52
  53 void
  54 __rtld_malloc_init_stubs (void)
  55 {
  56   __rtld_calloc = &rtld_calloc;
  57   __rtld_free = &rtld_free;
  58   __rtld_malloc = &rtld_malloc;
  59   __rtld_realloc = &rtld_realloc;
  60 }
  61
  62 bool
  63 __rtld_malloc_is_complete (void)
  64 {
  65   /* The caller assumes that there is an active malloc.  */
  66   assert (__rtld_malloc != NULL);
  67   return __rtld_malloc != &rtld_malloc;
  68 }
  69
  70 /* Lookup NAME at VERSION in the scope of MATCH.  */
  71 static void *
  72 lookup_malloc_symbol (struct link_map *main_map, const char *name,
  73                       struct r_found_version *version)
  74 {
  75
  76   const ElfW(Sym) *ref = NULL;
  77   lookup_t result = _dl_lookup_symbol_x (name, main_map, &ref,
  78                                          main_map->l_scope,
  79                                          version, 0, 0, NULL);
  80
  81   assert (ELFW(ST_TYPE) (ref->st_info) != STT_TLS);
  82   void *value = DL_SYMBOL_ADDRESS (result, ref);
  83
  84   return _dl_sym_post (result, ref, value, 0, main_map);
  85 }
  86
  87 void
  88 __rtld_malloc_init_real (struct link_map *main_map)
  89 {
  90   /* We cannot use relocations and initializers for this because the
  91      changes made by __rtld_malloc_init_stubs break REL-style
  92      (non-RELA) relocations that depend on the previous pointer
  93      contents.  Also avoid direct relocation depedencies for the
  94      malloc symbols so this function can be called before the final
  95      rtld relocation (which enables RELRO, after which the pointer
  96      variables cannot be written to).  */
  97
  98   struct r_found_version version;
  99   version.name = symbol_version_string (libc, GLIBC_2_0);
 100   version.hidden = 0;
 101   version.hash = _dl_elf_hash (version.name);
 102   version.filename = NULL;
 103
 104   void *new_calloc = lookup_malloc_symbol (main_map, "calloc", &version);
 105   void *new_free = lookup_malloc_symbol (main_map, "free", &version);
 106   void *new_malloc = lookup_malloc_symbol (main_map, "malloc", &version);
 107   void *new_realloc = lookup_malloc_symbol (main_map, "realloc", &version);
 108
 109   /* Update the pointers in one go, so that any internal allocations
 110      performed by lookup_malloc_symbol see a consistent
 111      implementation.  */
 112   __rtld_calloc = new_calloc;
 113   __rtld_free = new_free;
 114   __rtld_malloc = new_malloc;
 115   __rtld_realloc = new_realloc;
 116 }
 117
 118 /* Minimal malloc allocator for used during initial link.  After the
 119    initial link, a full malloc implementation is interposed, either
 120    the one in libc, or a different one supplied by the user through
 121    interposition.  */
 122
 123 static void *alloc_ptr, *alloc_end, *alloc_last_block;
 124
 125 /* Allocate an aligned memory block.  */
 126 static void *
 127 rtld_malloc (size_t n)
 128 {
 129   if (alloc_end == 0)
 130     {
 131       /* Consume any unused space in the last page of our data segment.  */
 132       extern int _end attribute_hidden;
 133       alloc_ptr = &_end;
 134       alloc_end = (void *) 0 + (((alloc_ptr - (void *) 0)
 135                                  + GLRO(dl_pagesize) - 1)
 136                                 & ~(GLRO(dl_pagesize) - 1));
 137     }
 138
 139   /* Make sure the allocation pointer is ideally aligned.  */
 140   alloc_ptr = (void *) 0 + (((alloc_ptr - (void *) 0) + MALLOC_ALIGNMENT - 1)
 141                             & ~(MALLOC_ALIGNMENT - 1));
 142
 143   if (alloc_ptr + n >= alloc_end || n >= -(uintptr_t) alloc_ptr)
 144     {
 145       /* Insufficient space left; allocate another page plus one extra
 146          page to reduce number of mmap calls.  */
 147       caddr_t page;
 148       size_t nup = (n + GLRO(dl_pagesize) - 1) & ~(GLRO(dl_pagesize) - 1);
 149       if (__glibc_unlikely (nup == 0 && n != 0))
 150         return NULL;
 151       nup += GLRO(dl_pagesize);
 152       page = __mmap (0, nup, PROT_READ|PROT_WRITE,
 153                      MAP_ANON|MAP_PRIVATE, -1, 0);
 154       if (page == MAP_FAILED)
 155         return NULL;
 156       if (page != alloc_end)
 157         alloc_ptr = page;
 158       alloc_end = page + nup;
 159     }
 160
 161   alloc_last_block = (void *) alloc_ptr;
 162   alloc_ptr += n;
 163   return alloc_last_block;
 164 }
 165
 166 /* We use this function occasionally since the real implementation may
 167    be optimized when it can assume the memory it returns already is
 168    set to NUL.  */
 169 static void *
 170 rtld_calloc (size_t nmemb, size_t size)
 171 {
 172   /* New memory from the trivial malloc above is always already cleared.
 173      (We make sure that's true in the rare occasion it might not be,
 174      by clearing memory in free, below.)  */
 175   size_t bytes = nmemb * size;
 176
 177 #define HALF_SIZE_T (((size_t) 1) << (8 * sizeof (size_t) / 2))
 178   if (__builtin_expect ((nmemb | size) >= HALF_SIZE_T, 0)
 179       && size != 0 && bytes / size != nmemb)
 180     return NULL;
 181
 182   return malloc (bytes);
 183 }
 184
 185 /* This will rarely be called.  */
 186 void
 187 rtld_free (void *ptr)
 188 {
 189   /* We can free only the last block allocated.  */
 190   if (ptr == alloc_last_block)
 191     {
 192       /* Since this is rare, we clear the freed block here
 193          so that calloc can presume malloc returns cleared memory.  */
 194       memset (alloc_last_block, '\0', alloc_ptr - alloc_last_block);
 195       alloc_ptr = alloc_last_block;
 196     }
 197 }
 198
 199 /* This is only called with the most recent block returned by malloc.  */
 200 void *
 201 rtld_realloc (void *ptr, size_t n)
 202 {
 203   if (ptr == NULL)
 204     return malloc (n);
 205   assert (ptr == alloc_last_block);
 206   size_t old_size = alloc_ptr - alloc_last_block;
 207   alloc_ptr = alloc_last_block;
 208   void *new = malloc (n);
 209   return new != ptr ? memcpy (new, ptr, old_size) : new;
 210 }
 211 \f
 212 /* Avoid signal frobnication in setjmp/longjmp.  Keeps things smaller.  */
 213
 214 #include <setjmp.h>
 215
 216 int weak_function
 217 __sigjmp_save (sigjmp_buf env, int savemask __attribute__ ((unused)))
 218 {
 219   env[0].__mask_was_saved = 0;
 220   return 0;
 221 }
 222 \f
 223 /* Define our own version of the internal function used by strerror.  We
 224    only provide the messages for some common errors.  This avoids pulling
 225    in the whole error list.  */
 226
 227 char * weak_function
 228 __strerror_r (int errnum, char *buf, size_t buflen)
 229 {
 230   char *msg;
 231
 232   switch (errnum)
 233     {
 234     case ENOMEM:
 235       msg = (char *) "Cannot allocate memory";
 236       break;
 237     case EINVAL:
 238       msg = (char *) "Invalid argument";
 239       break;
 240     case ENOENT:
 241       msg = (char *) "No such file or directory";
 242       break;
 243     case EPERM:
 244       msg = (char *) "Operation not permitted";
 245       break;
 246     case EIO:
 247       msg = (char *) "Input/output error";
 248       break;
 249     case EACCES:
 250       msg = (char *) "Permission denied";
 251       break;
 252     default:
 253       /* No need to check buffer size, all calls in the dynamic linker
 254          provide enough space.  */
 255       buf[buflen - 1] = '\0';
 256       msg = _itoa (errnum, buf + buflen - 1, 10, 0);
 257       msg = memcpy (msg - (sizeof ("Error ") - 1), "Error ",
 258                     sizeof ("Error ") - 1);
 259       break;
 260     }
 261
 262   return msg;
 263 }
 264 \f
 265 void
 266 __libc_fatal (const char *message)
 267 {
 268   _dl_fatal_printf ("%s", message);
 269 }
 270 rtld_hidden_def (__libc_fatal)
 271
 272 void
 273 __attribute__ ((noreturn))
 274 __chk_fail (void)
 275 {
 276   _exit (127);
 277 }
 278 rtld_hidden_def (__chk_fail)
 279
 280 #ifndef NDEBUG
 281 /* Define (weakly) our own assert failure function which doesn't use stdio.
 282    If we are linked into the user program (-ldl), the normal __assert_fail
 283    defn can override this one.  */
 284
 285 void weak_function
 286 __assert_fail (const char *assertion,
 287                const char *file, unsigned int line, const char *function)
 288 {
 289   _dl_fatal_printf ("\
 290 Inconsistency detected by ld.so: %s: %u: %s%sAssertion `%s' failed!\n",
 291                     file, line, function ?: "", function ? ": " : "",
 292                     assertion);
 293
 294 }
 295 # ifndef NO_RTLD_HIDDEN
 296 rtld_hidden_weak (__assert_fail)
 297 # endif
 298
 299 void weak_function
 300 __assert_perror_fail (int errnum,
 301                       const char *file, unsigned int line,
 302                       const char *function)
 303 {
 304   char errbuf[400];
 305   _dl_fatal_printf ("\
 306 Inconsistency detected by ld.so: %s: %u: %s%sUnexpected error: %s.\n",
 307                     file, line, function ?: "", function ? ": " : "",
 308                     __strerror_r (errnum, errbuf, sizeof errbuf));
 309
 310 }
 311 # ifndef NO_RTLD_HIDDEN
 312 rtld_hidden_weak (__assert_perror_fail)
 313 # endif
 314 #endif
 315 \f
 316 #undef _itoa
 317 /* We always use _itoa instead of _itoa_word in ld.so since the former
 318    also has to be present and it is never about speed when these
 319    functions are used.  */
 320 char *
 321 _itoa (unsigned long long int value, char *buflim, unsigned int base,
 322        int upper_case)
 323 {
 324   assert (! upper_case);
 325
 326   do
 327     *--buflim = _itoa_lower_digits[value % base];
 328   while ((value /= base) != 0);
 329
 330   return buflim;
 331 }
 332
 333 /* The '_itoa_lower_digits' variable in libc.so is able to handle bases
 334    up to 36.  We don't need this here.  */
 335 const char _itoa_lower_digits[16] = "0123456789abcdef";
 336 rtld_hidden_data_def (_itoa_lower_digits)
 337 \f
 338 /* The following is not a complete strsep implementation.  It cannot
 339    handle empty delimiter strings.  But this isn't necessary for the
 340    execution of ld.so.  */
 341 #undef strsep
 342 #undef __strsep
 343 char *
 344 __strsep (char **stringp, const char *delim)
 345 {
 346   char *begin;
 347
 348   assert (delim[0] != '\0');
 349
 350   begin = *stringp;
 351   if (begin != NULL)
 352     {
 353       char *end = begin;
 354
 355       while (*end != '\0' || (end = NULL))
 356         {
 357           const char *dp = delim;
 358
 359           do
 360             if (*dp == *end)
 361               break;
 362           while (*++dp != '\0');
 363
 364           if (*dp != '\0')
 365             {
 366               *end++ = '\0';
 367               break;
 368             }
 369
 370           ++end;
 371         }
 372
 373       *stringp = end;
 374     }
 375
 376   return begin;
 377 }
 378 weak_alias (__strsep, strsep)
 379 strong_alias (__strsep, __strsep_g)