elf/dl-support.c

   1 /* Support for dynamic linking code in static libc.
   2    Copyright (C) 1996-2023 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-procinfo.h>
  39 #include <unsecvars.h>
  40 #include <hp-timing.h>
  41 #include <stackinfo.h>
  42 #include <dl-vdso.h>
  43 #include <dl-vdso-setup.h>
  44 #include <dl-auxv.h>
  45 #include <dl-find_object.h>
  46 #include <array_length.h>
  47 #include <dl-symbol-redir-ifunc.h>
  48
  49 extern char *__progname;
  50 char **_dl_argv = &__progname;  /* This is checked for some error messages.  */
  51
  52 /* Name of the architecture.  */
  53 const char *_dl_platform;
  54 size_t _dl_platformlen;
  55
  56 int _dl_debug_mask;
  57 int _dl_lazy;
  58 int _dl_dynamic_weak;
  59
  60 /* If nonzero print warnings about problematic situations.  */
  61 int _dl_verbose;
  62
  63 /* We never do profiling.  */
  64 const char *_dl_profile;
  65 const char *_dl_profile_output;
  66
  67 /* Names of shared object for which the RUNPATHs and RPATHs should be
  68    ignored.  */
  69 const char *_dl_inhibit_rpath;
  70
  71 /* The map for the object we will profile.  */
  72 struct link_map *_dl_profile_map;
  73
  74 /* This is the address of the last stack address ever used.  */
  75 void *__libc_stack_end;
  76
  77 /* Path where the binary is found.  */
  78 const char *_dl_origin_path;
  79
  80 /* Nonzero if runtime lookup should not update the .got/.plt.  */
  81 int _dl_bind_not;
  82
  83 /* A dummy link map for the executable, used by dlopen to access the global
  84    scope.  We don't export any symbols ourselves, so this can be minimal.  */
  85 static struct link_map _dl_main_map =
  86   {
  87     .l_name = (char *) "",
  88     .l_real = &_dl_main_map,
  89     .l_ns = LM_ID_BASE,
  90     .l_libname = &(struct libname_list) { .name = "", .dont_free = 1 },
  91     .l_searchlist =
  92       {
  93         .r_list = &(struct link_map *) { &_dl_main_map },
  94         .r_nlist = 1,
  95       },
  96     .l_symbolic_searchlist = { .r_list = &(struct link_map *) { NULL } },
  97     .l_type = lt_executable,
  98     .l_scope_mem = { &_dl_main_map.l_searchlist },
  99     .l_scope_max = (sizeof (_dl_main_map.l_scope_mem)
 100                     / sizeof (_dl_main_map.l_scope_mem[0])),
 101     .l_scope = _dl_main_map.l_scope_mem,
 102     .l_local_scope = { &_dl_main_map.l_searchlist },
 103     .l_used = 1,
 104     .l_tls_offset = NO_TLS_OFFSET,
 105     .l_serial = 1,
 106   };
 107
 108 /* Namespace information.  */
 109 struct link_namespaces _dl_ns[DL_NNS] =
 110   {
 111     [LM_ID_BASE] =
 112       {
 113         ._ns_loaded = &_dl_main_map,
 114         ._ns_nloaded = 1,
 115         ._ns_main_searchlist = &_dl_main_map.l_searchlist,
 116       }
 117   };
 118 size_t _dl_nns = 1;
 119
 120 /* Incremented whenever something may have been added to dl_loaded. */
 121 unsigned long long _dl_load_adds = 1;
 122
 123 /* Fake scope of the main application.  */
 124 struct r_scope_elem _dl_initial_searchlist =
 125   {
 126     .r_list = &(struct link_map *) { &_dl_main_map },
 127     .r_nlist = 1,
 128   };
 129
 130 #ifndef HAVE_INLINED_SYSCALLS
 131 /* Nonzero during startup.  */
 132 int _dl_starting_up = 1;
 133 #endif
 134
 135 /* Random data provided by the kernel.  */
 136 void *_dl_random;
 137
 138 /* Get architecture specific initializer.  */
 139 #include <dl-procruntime.c>
 140 #include <dl-procinfo.c>
 141
 142 size_t _dl_pagesize = EXEC_PAGESIZE;
 143
 144 size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;
 145
 146 int _dl_inhibit_cache;
 147
 148 /* All known directories in sorted order.  */
 149 struct r_search_path_elem *_dl_all_dirs;
 150
 151 /* All directories after startup.  */
 152 struct r_search_path_elem *_dl_init_all_dirs;
 153
 154 /* The object to be initialized first.  */
 155 struct link_map *_dl_initfirst;
 156
 157 /* Descriptor to write debug messages to.  */
 158 int _dl_debug_fd = STDERR_FILENO;
 159
 160 ElfW(auxv_t) *_dl_auxv;
 161 const ElfW(Phdr) *_dl_phdr;
 162 size_t _dl_phnum;
 163 uint64_t _dl_hwcap;
 164 uint64_t _dl_hwcap2;
 165
 166 enum dso_sort_algorithm _dl_dso_sort_algo;
 167
 168 /* The value of the FPU control word the kernel will preset in hardware.  */
 169 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 170
 171 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 172  * executable but this isn't true for all platforms.  */
 173 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
 174
 175 #if PTHREAD_IN_LIBC
 176 list_t _dl_stack_used;
 177 list_t _dl_stack_user;
 178 list_t _dl_stack_cache;
 179 size_t _dl_stack_cache_actsize;
 180 uintptr_t _dl_in_flight_stack;
 181 int _dl_stack_cache_lock;
 182 #else
 183 /* If loading a shared object requires that we make the stack executable
 184    when it was not, we do it by calling this function.
 185    It returns an errno code or zero on success.  */
 186 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 187 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 188 #endif
 189 struct dl_scope_free_list *_dl_scope_free_list;
 190
 191 #ifdef NEED_DL_SYSINFO
 192 /* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
 193    initialize it here to avoid RELATIVE relocation in static PIE.  */
 194 uintptr_t _dl_sysinfo;
 195 #endif
 196 #ifdef NEED_DL_SYSINFO_DSO
 197 /* Address of the ELF headers in the vsyscall page.  */
 198 const ElfW(Ehdr) *_dl_sysinfo_dso;
 199
 200 struct link_map *_dl_sysinfo_map;
 201
 202 # include "get-dynamic-info.h"
 203 #endif
 204 #include "setup-vdso.h"
 205 /* Define the vDSO function pointers.  */
 206 #include <dl-vdso-setup.c>
 207
 208 /* During the program run we must not modify the global data of
 209    loaded shared object simultanously in two threads.  Therefore we
 210    protect `_dl_open' and `_dl_close' in dl-close.c.
 211
 212    This must be a recursive lock since the initializer function of
 213    the loaded object might as well require a call to this function.
 214    At this time it is not anymore a problem to modify the tables.  */
 215 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
 216 /* This lock is used to keep __dl_iterate_phdr from inspecting the
 217    list of loaded objects while an object is added to or removed from
 218    that list.  */
 219 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
 220   /* This lock protects global and module specific TLS related data.
 221      E.g. it is held in dlopen and dlclose when GL(dl_tls_generation),
 222      GL(dl_tls_max_dtv_idx) or GL(dl_tls_dtv_slotinfo_list) are
 223      accessed and when TLS related relocations are processed for a
 224      module.  It was introduced to keep pthread_create accessing TLS
 225      state that is being set up.  */
 226 __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
 227
 228
 229 #ifdef HAVE_AUX_VECTOR
 230 #include <dl-parse_auxv.h>
 231
 232 int _dl_clktck;
 233
 234 void
 235 _dl_aux_init (ElfW(auxv_t) *av)
 236 {
 237 #ifdef NEED_DL_SYSINFO
 238   /* NB: Avoid RELATIVE relocation in static PIE.  */
 239   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 240 #endif
 241
 242   _dl_auxv = av;
 243   dl_parse_auxv_t auxv_values;
 244   /* Use an explicit initialization loop here because memset may not
 245      be available yet.  */
 246   for (int i = 0; i < array_length (auxv_values); ++i)
 247     auxv_values[i] = 0;
 248   _dl_parse_auxv (av, auxv_values);
 249
 250   _dl_phdr = (void*) auxv_values[AT_PHDR];
 251   _dl_phnum = auxv_values[AT_PHNUM];
 252
 253   if (_dl_phdr == NULL)
 254     {
 255       /* Starting from binutils-2.23, the linker will define the
 256          magic symbol __ehdr_start to point to our own ELF header
 257          if it is visible in a segment that also includes the phdrs.
 258          So we can set up _dl_phdr and _dl_phnum even without any
 259          information from auxv.  */
 260
 261       extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
 262       assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
 263       _dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
 264       _dl_phnum = __ehdr_start.e_phnum;
 265     }
 266
 267   assert (_dl_phdr != NULL);
 268 }
 269 #endif
 270
 271
 272 void
 273 _dl_non_dynamic_init (void)
 274 {
 275   _dl_main_map.l_origin = _dl_get_origin ();
 276   _dl_main_map.l_phdr = GL(dl_phdr);
 277   _dl_main_map.l_phnum = GL(dl_phnum);
 278
 279   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 280
 281   /* Set up the data structures for the system-supplied DSO early,
 282      so they can influence _dl_init_paths.  */
 283   setup_vdso (NULL, NULL);
 284
 285   /* With vDSO setup we can initialize the function pointers.  */
 286   setup_vdso_pointers ();
 287
 288   /* Initialize the data structures for the search paths for shared
 289      objects.  */
 290   _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
 291                   /* No glibc-hwcaps selection support in statically
 292                      linked binaries.  */
 293                   NULL, NULL);
 294
 295   /* Remember the last search directory added at startup.  */
 296   _dl_init_all_dirs = GL(dl_all_dirs);
 297
 298   _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 299
 300   _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
 301
 302   _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
 303
 304   _dl_profile_output = getenv ("LD_PROFILE_OUTPUT");
 305   if (_dl_profile_output == NULL || _dl_profile_output[0] == '\0')
 306     _dl_profile_output
 307       = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];
 308
 309   if (__libc_enable_secure)
 310     {
 311       static const char unsecure_envvars[] =
 312         UNSECURE_ENVVARS
 313         ;
 314       const char *cp = unsecure_envvars;
 315
 316       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 317         {
 318           __unsetenv (cp);
 319           cp = strchr (cp, '\0') + 1;
 320         }
 321     }
 322
 323 #ifdef DL_PLATFORM_INIT
 324   DL_PLATFORM_INIT;
 325 #endif
 326
 327   /* Now determine the length of the platform string.  */
 328   if (_dl_platform != NULL)
 329     _dl_platformlen = strlen (_dl_platform);
 330
 331   for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 332     switch (ph->p_type)
 333       {
 334       /* Check if the stack is nonexecutable.  */
 335       case PT_GNU_STACK:
 336         _dl_stack_flags = ph->p_flags;
 337         break;
 338
 339       case PT_GNU_RELRO:
 340         _dl_main_map.l_relro_addr = ph->p_vaddr;
 341         _dl_main_map.l_relro_size = ph->p_memsz;
 342         break;
 343       }
 344
 345   call_function_static_weak (_dl_find_object_init);
 346
 347   /* Setup relro on the binary itself.  */
 348   if (_dl_main_map.l_relro_size != 0)
 349     _dl_protect_relro (&_dl_main_map);
 350 }
 351
 352 #ifdef DL_SYSINFO_IMPLEMENTATION
 353 DL_SYSINFO_IMPLEMENTATION
 354 #endif
 355
 356 #if ENABLE_STATIC_PIE
 357 /* Since relocation to hidden _dl_main_map causes relocation overflow on
 358    aarch64, a function is used to get the address of _dl_main_map.  */
 359
 360 struct link_map *
 361 _dl_get_dl_main_map (void)
 362 {
 363   return &_dl_main_map;
 364 }
 365 #endif
 366
 367 /* This is used by _dl_runtime_profile, not used on static code.  */
 368 void
 369 DL_ARCH_FIXUP_ATTRIBUTE
 370 _dl_audit_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 371                    const void *inregs, void *outregs)
 372 {
 373 }