elf/dl-support.c

   1 /* Support for dynamic linking code in static libc.
   2    Copyright (C) 1996-2021 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 /* This file defines some things that for the dynamic linker are defined in
  20    rtld.c and dl-sysdep.c in ways appropriate to bootstrap dynamic linking.  */
  21
  22 #include <string.h>
  23 /* Mark symbols hidden in static PIE for early self relocation to work.
  24    Note: string.h may have ifuncs which cannot be hidden on i686.  */
  25 #if BUILD_PIE_DEFAULT
  26 # pragma GCC visibility push(hidden)
  27 #endif
  28 #include <errno.h>
  29 #include <libintl.h>
  30 #include <stdlib.h>
  31 #include <unistd.h>
  32 #include <sys/param.h>
  33 #include <stdint.h>
  34 #include <ldsodefs.h>
  35 #include <dl-machine.h>
  36 #include <libc-lock.h>
  37 #include <dl-cache.h>
  38 #include <dl-librecon.h>
  39 #include <dl-procinfo.h>
  40 #include <unsecvars.h>
  41 #include <hp-timing.h>
  42 #include <stackinfo.h>
  43 #include <dl-vdso.h>
  44 #include <dl-vdso-setup.h>
  45 #include <dl-auxv.h>
  46
  47 extern char *__progname;
  48 char **_dl_argv = &__progname;  /* This is checked for some error messages.  */
  49
  50 /* Name of the architecture.  */
  51 const char *_dl_platform;
  52 size_t _dl_platformlen;
  53
  54 int _dl_debug_mask;
  55 int _dl_lazy;
  56 ElfW(Addr) _dl_use_load_bias = -2;
  57 int _dl_dynamic_weak;
  58
  59 /* If nonzero print warnings about problematic situations.  */
  60 int _dl_verbose;
  61
  62 /* We never do profiling.  */
  63 const char *_dl_profile;
  64 const char *_dl_profile_output;
  65
  66 /* Names of shared object for which the RUNPATHs and RPATHs should be
  67    ignored.  */
  68 const char *_dl_inhibit_rpath;
  69
  70 /* The map for the object we will profile.  */
  71 struct link_map *_dl_profile_map;
  72
  73 /* This is the address of the last stack address ever used.  */
  74 void *__libc_stack_end;
  75
  76 /* Path where the binary is found.  */
  77 const char *_dl_origin_path;
  78
  79 /* Nonzero if runtime lookup should not update the .got/.plt.  */
  80 int _dl_bind_not;
  81
  82 /* A dummy link map for the executable, used by dlopen to access the global
  83    scope.  We don't export any symbols ourselves, so this can be minimal.  */
  84 static struct link_map _dl_main_map =
  85   {
  86     .l_name = (char *) "",
  87     .l_real = &_dl_main_map,
  88     .l_ns = LM_ID_BASE,
  89     .l_libname = &(struct libname_list) { .name = "", .dont_free = 1 },
  90     .l_searchlist =
  91       {
  92         .r_list = &(struct link_map *) { &_dl_main_map },
  93         .r_nlist = 1,
  94       },
  95     .l_symbolic_searchlist = { .r_list = &(struct link_map *) { NULL } },
  96     .l_type = lt_executable,
  97     .l_scope_mem = { &_dl_main_map.l_searchlist },
  98     .l_scope_max = (sizeof (_dl_main_map.l_scope_mem)
  99                     / sizeof (_dl_main_map.l_scope_mem[0])),
 100     .l_scope = _dl_main_map.l_scope_mem,
 101     .l_local_scope = { &_dl_main_map.l_searchlist },
 102     .l_used = 1,
 103     .l_tls_offset = NO_TLS_OFFSET,
 104     .l_serial = 1,
 105   };
 106
 107 /* Namespace information.  */
 108 struct link_namespaces _dl_ns[DL_NNS] =
 109   {
 110     [LM_ID_BASE] =
 111       {
 112         ._ns_loaded = &_dl_main_map,
 113         ._ns_nloaded = 1,
 114         ._ns_main_searchlist = &_dl_main_map.l_searchlist,
 115       }
 116   };
 117 size_t _dl_nns = 1;
 118
 119 /* Incremented whenever something may have been added to dl_loaded. */
 120 unsigned long long _dl_load_adds = 1;
 121
 122 /* Fake scope of the main application.  */
 123 struct r_scope_elem _dl_initial_searchlist =
 124   {
 125     .r_list = &(struct link_map *) { &_dl_main_map },
 126     .r_nlist = 1,
 127   };
 128
 129 #ifndef HAVE_INLINED_SYSCALLS
 130 /* Nonzero during startup.  */
 131 int _dl_starting_up = 1;
 132 #endif
 133
 134 /* Random data provided by the kernel.  */
 135 void *_dl_random;
 136
 137 /* Get architecture specific initializer.  */
 138 #include <dl-procruntime.c>
 139 #include <dl-procinfo.c>
 140
 141 size_t _dl_pagesize = EXEC_PAGESIZE;
 142
 143 size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;
 144
 145 int _dl_inhibit_cache;
 146
 147 unsigned int _dl_osversion;
 148
 149 /* All known directories in sorted order.  */
 150 struct r_search_path_elem *_dl_all_dirs;
 151
 152 /* All directories after startup.  */
 153 struct r_search_path_elem *_dl_init_all_dirs;
 154
 155 /* The object to be initialized first.  */
 156 struct link_map *_dl_initfirst;
 157
 158 /* Descriptor to write debug messages to.  */
 159 int _dl_debug_fd = STDERR_FILENO;
 160
 161 int _dl_correct_cache_id = _DL_CACHE_DEFAULT_ID;
 162
 163 ElfW(auxv_t) *_dl_auxv;
 164 const ElfW(Phdr) *_dl_phdr;
 165 size_t _dl_phnum;
 166 uint64_t _dl_hwcap;
 167 uint64_t _dl_hwcap2;
 168
 169 /* The value of the FPU control word the kernel will preset in hardware.  */
 170 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 171
 172 #if !HAVE_TUNABLES
 173 /* This is not initialized to HWCAP_IMPORTANT, matching the definition
 174    of _dl_important_hwcaps, below, where no hwcap strings are ever
 175    used.  This mask is still used to mediate the lookups in the cache
 176    file.  Since there is no way to set this nonzero (we don't grok the
 177    LD_HWCAP_MASK environment variable here), there is no real point in
 178    setting _dl_hwcap nonzero below, but we do anyway.  */
 179 uint64_t _dl_hwcap_mask;
 180 #endif
 181
 182 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 183  * executable but this isn't true for all platforms.  */
 184 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
 185
 186 #if PTHREAD_IN_LIBC
 187 list_t _dl_stack_used;
 188 list_t _dl_stack_user;
 189 list_t _dl_stack_cache;
 190 size_t _dl_stack_cache_actsize;
 191 uintptr_t _dl_in_flight_stack;
 192 int _dl_stack_cache_lock;
 193 #else
 194 /* If loading a shared object requires that we make the stack executable
 195    when it was not, we do it by calling this function.
 196    It returns an errno code or zero on success.  */
 197 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 198 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 199 #endif
 200 struct dl_scope_free_list *_dl_scope_free_list;
 201
 202 #ifdef NEED_DL_SYSINFO
 203 /* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
 204    initialize it here to avoid RELATIVE relocation in static PIE.  */
 205 uintptr_t _dl_sysinfo;
 206 #endif
 207 #ifdef NEED_DL_SYSINFO_DSO
 208 /* Address of the ELF headers in the vsyscall page.  */
 209 const ElfW(Ehdr) *_dl_sysinfo_dso;
 210
 211 struct link_map *_dl_sysinfo_map;
 212
 213 # include "get-dynamic-info.h"
 214 #endif
 215 #include "setup-vdso.h"
 216 /* Define the vDSO function pointers.  */
 217 #include <dl-vdso-setup.c>
 218
 219 /* During the program run we must not modify the global data of
 220    loaded shared object simultanously in two threads.  Therefore we
 221    protect `_dl_open' and `_dl_close' in dl-close.c.
 222
 223    This must be a recursive lock since the initializer function of
 224    the loaded object might as well require a call to this function.
 225    At this time it is not anymore a problem to modify the tables.  */
 226 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
 227 /* This lock is used to keep __dl_iterate_phdr from inspecting the
 228    list of loaded objects while an object is added to or removed from
 229    that list.  */
 230 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
 231
 232
 233 #ifdef HAVE_AUX_VECTOR
 234 int _dl_clktck;
 235
 236 void
 237 _dl_aux_init (ElfW(auxv_t) *av)
 238 {
 239   int seen = 0;
 240   uid_t uid = 0;
 241   gid_t gid = 0;
 242
 243 #ifdef NEED_DL_SYSINFO
 244   /* NB: Avoid RELATIVE relocation in static PIE.  */
 245   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 246 #endif
 247
 248   _dl_auxv = av;
 249   for (; av->a_type != AT_NULL; ++av)
 250     switch (av->a_type)
 251       {
 252       case AT_PAGESZ:
 253         if (av->a_un.a_val != 0)
 254           GLRO(dl_pagesize) = av->a_un.a_val;
 255         break;
 256       case AT_CLKTCK:
 257         GLRO(dl_clktck) = av->a_un.a_val;
 258         break;
 259       case AT_PHDR:
 260         GL(dl_phdr) = (const void *) av->a_un.a_val;
 261         break;
 262       case AT_PHNUM:
 263         GL(dl_phnum) = av->a_un.a_val;
 264         break;
 265       case AT_PLATFORM:
 266         GLRO(dl_platform) = (void *) av->a_un.a_val;
 267         break;
 268       case AT_HWCAP:
 269         GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
 270         break;
 271       case AT_HWCAP2:
 272         GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
 273         break;
 274       case AT_FPUCW:
 275         GLRO(dl_fpu_control) = av->a_un.a_val;
 276         break;
 277 #ifdef NEED_DL_SYSINFO
 278       case AT_SYSINFO:
 279         GL(dl_sysinfo) = av->a_un.a_val;
 280         break;
 281 #endif
 282 #ifdef NEED_DL_SYSINFO_DSO
 283       case AT_SYSINFO_EHDR:
 284         GL(dl_sysinfo_dso) = (void *) av->a_un.a_val;
 285         break;
 286 #endif
 287       case AT_UID:
 288         uid ^= av->a_un.a_val;
 289         seen |= 1;
 290         break;
 291       case AT_EUID:
 292         uid ^= av->a_un.a_val;
 293         seen |= 2;
 294         break;
 295       case AT_GID:
 296         gid ^= av->a_un.a_val;
 297         seen |= 4;
 298         break;
 299       case AT_EGID:
 300         gid ^= av->a_un.a_val;
 301         seen |= 8;
 302         break;
 303       case AT_SECURE:
 304         seen = -1;
 305         __libc_enable_secure = av->a_un.a_val;
 306         __libc_enable_secure_decided = 1;
 307         break;
 308       case AT_RANDOM:
 309         _dl_random = (void *) av->a_un.a_val;
 310         break;
 311       case AT_MINSIGSTKSZ:
 312         _dl_minsigstacksize = av->a_un.a_val;
 313         break;
 314       DL_PLATFORM_AUXV
 315       }
 316   if (seen == 0xf)
 317     {
 318       __libc_enable_secure = uid != 0 || gid != 0;
 319       __libc_enable_secure_decided = 1;
 320     }
 321 }
 322 #endif
 323
 324
 325 void
 326 _dl_non_dynamic_init (void)
 327 {
 328   _dl_main_map.l_origin = _dl_get_origin ();
 329   _dl_main_map.l_phdr = GL(dl_phdr);
 330   _dl_main_map.l_phnum = GL(dl_phnum);
 331
 332   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 333
 334   /* Set up the data structures for the system-supplied DSO early,
 335      so they can influence _dl_init_paths.  */
 336   setup_vdso (NULL, NULL);
 337
 338   /* With vDSO setup we can initialize the function pointers.  */
 339   setup_vdso_pointers ();
 340
 341   /* Initialize the data structures for the search paths for shared
 342      objects.  */
 343   _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
 344                   /* No glibc-hwcaps selection support in statically
 345                      linked binaries.  */
 346                   NULL, NULL);
 347
 348   /* Remember the last search directory added at startup.  */
 349   _dl_init_all_dirs = GL(dl_all_dirs);
 350
 351   _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 352
 353   _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
 354
 355   _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
 356
 357   _dl_profile_output = getenv ("LD_PROFILE_OUTPUT");
 358   if (_dl_profile_output == NULL || _dl_profile_output[0] == '\0')
 359     _dl_profile_output
 360       = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];
 361
 362   if (__libc_enable_secure)
 363     {
 364       static const char unsecure_envvars[] =
 365         UNSECURE_ENVVARS
 366 #ifdef EXTRA_UNSECURE_ENVVARS
 367         EXTRA_UNSECURE_ENVVARS
 368 #endif
 369         ;
 370       const char *cp = unsecure_envvars;
 371
 372       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 373         {
 374           __unsetenv (cp);
 375           cp = (const char *) __rawmemchr (cp, '\0') + 1;
 376         }
 377
 378 #if !HAVE_TUNABLES
 379       if (__access ("/etc/suid-debug", F_OK) != 0)
 380         __unsetenv ("MALLOC_CHECK_");
 381 #endif
 382     }
 383
 384 #ifdef DL_PLATFORM_INIT
 385   DL_PLATFORM_INIT;
 386 #endif
 387
 388 #ifdef DL_OSVERSION_INIT
 389   DL_OSVERSION_INIT;
 390 #endif
 391
 392   /* Now determine the length of the platform string.  */
 393   if (_dl_platform != NULL)
 394     _dl_platformlen = strlen (_dl_platform);
 395
 396   if (_dl_phdr != NULL)
 397     for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 398       switch (ph->p_type)
 399         {
 400         /* Check if the stack is nonexecutable.  */
 401         case PT_GNU_STACK:
 402           _dl_stack_flags = ph->p_flags;
 403           break;
 404
 405         case PT_GNU_RELRO:
 406           _dl_main_map.l_relro_addr = ph->p_vaddr;
 407           _dl_main_map.l_relro_size = ph->p_memsz;
 408           break;
 409         }
 410
 411   /* Setup relro on the binary itself.  */
 412   if (_dl_main_map.l_relro_size != 0)
 413     _dl_protect_relro (&_dl_main_map);
 414 }
 415
 416 #ifdef DL_SYSINFO_IMPLEMENTATION
 417 DL_SYSINFO_IMPLEMENTATION
 418 #endif
 419
 420 #if ENABLE_STATIC_PIE
 421 /* Since relocation to hidden _dl_main_map causes relocation overflow on
 422    aarch64, a function is used to get the address of _dl_main_map.  */
 423
 424 struct link_map *
 425 _dl_get_dl_main_map (void)
 426 {
 427   return &_dl_main_map;
 428 }
 429 #endif