elf/dl-support.c

   1 /* Support for dynamic linking code in static libc.
   2    Copyright (C) 1996-2024 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 /* Names of shared object for which the RUNPATHs and RPATHs should be
  64    ignored.  */
  65 const char *_dl_inhibit_rpath;
  66
  67 /* The map for the object we will profile.  */
  68 struct link_map *_dl_profile_map;
  69
  70 /* This is the address of the last stack address ever used.  */
  71 void *__libc_stack_end;
  72
  73 /* Path where the binary is found.  */
  74 const char *_dl_origin_path;
  75
  76 /* Nonzero if runtime lookup should not update the .got/.plt.  */
  77 int _dl_bind_not;
  78
  79 /* A dummy link map for the executable, used by dlopen to access the global
  80    scope.  We don't export any symbols ourselves, so this can be minimal.  */
  81 static struct link_map _dl_main_map =
  82   {
  83     .l_name = (char *) "",
  84     .l_real = &_dl_main_map,
  85     .l_ns = LM_ID_BASE,
  86     .l_libname = &(struct libname_list) { .name = "", .dont_free = 1 },
  87     .l_searchlist =
  88       {
  89         .r_list = &(struct link_map *) { &_dl_main_map },
  90         .r_nlist = 1,
  91       },
  92     .l_symbolic_searchlist = { .r_list = &(struct link_map *) { NULL } },
  93     .l_type = lt_executable,
  94     .l_scope_mem = { &_dl_main_map.l_searchlist },
  95     .l_scope_max = (sizeof (_dl_main_map.l_scope_mem)
  96                     / sizeof (_dl_main_map.l_scope_mem[0])),
  97     .l_scope = _dl_main_map.l_scope_mem,
  98     .l_local_scope = { &_dl_main_map.l_searchlist },
  99     .l_used = 1,
 100     .l_tls_offset = NO_TLS_OFFSET,
 101     .l_serial = 1,
 102   };
 103
 104 /* Namespace information.  */
 105 struct link_namespaces _dl_ns[DL_NNS] =
 106   {
 107     [LM_ID_BASE] =
 108       {
 109         ._ns_loaded = &_dl_main_map,
 110         ._ns_nloaded = 1,
 111         ._ns_main_searchlist = &_dl_main_map.l_searchlist,
 112       }
 113   };
 114 size_t _dl_nns = 1;
 115
 116 /* Incremented whenever something may have been added to dl_loaded. */
 117 unsigned long long _dl_load_adds = 1;
 118
 119 /* Fake scope of the main application.  */
 120 struct r_scope_elem _dl_initial_searchlist =
 121   {
 122     .r_list = &(struct link_map *) { &_dl_main_map },
 123     .r_nlist = 1,
 124   };
 125
 126 #ifndef HAVE_INLINED_SYSCALLS
 127 /* Nonzero during startup.  */
 128 int _dl_starting_up = 1;
 129 #endif
 130
 131 /* Random data provided by the kernel.  */
 132 void *_dl_random;
 133
 134 /* Get architecture specific initializer.  */
 135 #include <dl-procruntime.c>
 136 #include <dl-procinfo.c>
 137
 138 size_t _dl_pagesize
 139 #ifdef EXEC_PAGESIZE
 140   = EXEC_PAGESIZE
 141 #endif
 142 ;
 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 uint64_t _dl_hwcap3;
 166 uint64_t _dl_hwcap4;
 167
 168 enum dso_sort_algorithm _dl_dso_sort_algo;
 169
 170 /* The value of the FPU control word the kernel will preset in hardware.  */
 171 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 172
 173 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 174  * executable but this isn't true for all platforms.  */
 175 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
 176
 177 #if PTHREAD_IN_LIBC
 178 list_t _dl_stack_used;
 179 list_t _dl_stack_user;
 180 list_t _dl_stack_cache;
 181 size_t _dl_stack_cache_actsize;
 182 uintptr_t _dl_in_flight_stack;
 183 int _dl_stack_cache_lock;
 184 #else
 185 /* If loading a shared object requires that we make the stack executable
 186    when it was not, we do it by calling this function.
 187    It returns an errno code or zero on success.  */
 188 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 189 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 190 #endif
 191 struct dl_scope_free_list *_dl_scope_free_list;
 192
 193 #ifdef NEED_DL_SYSINFO
 194 /* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
 195    initialize it here to avoid RELATIVE relocation in static PIE.  */
 196 uintptr_t _dl_sysinfo;
 197 #endif
 198 #ifdef NEED_DL_SYSINFO_DSO
 199 /* Address of the ELF headers in the vsyscall page.  */
 200 const ElfW(Ehdr) *_dl_sysinfo_dso;
 201
 202 struct link_map *_dl_sysinfo_map;
 203
 204 # include "get-dynamic-info.h"
 205 #endif
 206 #include "setup-vdso.h"
 207 /* Define the vDSO function pointers.  */
 208 #include <dl-vdso-setup.c>
 209
 210 /* During the program run we must not modify the global data of
 211    loaded shared object simultaneously in two threads.  Therefore we
 212    protect `_dl_open' and `_dl_close' in dl-close.c.
 213
 214    This must be a recursive lock since the initializer function of
 215    the loaded object might as well require a call to this function.
 216    At this time it is not anymore a problem to modify the tables.  */
 217 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
 218 /* This lock is used to keep __dl_iterate_phdr from inspecting the
 219    list of loaded objects while an object is added to or removed from
 220    that list.  */
 221 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
 222   /* This lock protects global and module specific TLS related data.
 223      E.g. it is held in dlopen and dlclose when GL(dl_tls_generation),
 224      GL(dl_tls_max_dtv_idx) or GL(dl_tls_dtv_slotinfo_list) are
 225      accessed and when TLS related relocations are processed for a
 226      module.  It was introduced to keep pthread_create accessing TLS
 227      state that is being set up.  */
 228 __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
 229
 230
 231 #ifdef HAVE_AUX_VECTOR
 232 #include <dl-parse_auxv.h>
 233
 234 int _dl_clktck;
 235
 236 void
 237 _dl_aux_init (ElfW(auxv_t) *av)
 238 {
 239 #ifdef NEED_DL_SYSINFO
 240   /* NB: Avoid RELATIVE relocation in static PIE.  */
 241   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 242 #endif
 243
 244   _dl_auxv = av;
 245   dl_parse_auxv_t auxv_values;
 246   /* Use an explicit initialization loop here because memset may not
 247      be available yet.  */
 248   for (int i = 0; i < array_length (auxv_values); ++i)
 249     auxv_values[i] = 0;
 250   _dl_parse_auxv (av, auxv_values);
 251
 252   _dl_phdr = (void*) auxv_values[AT_PHDR];
 253   _dl_phnum = auxv_values[AT_PHNUM];
 254
 255   if (_dl_phdr == NULL)
 256     {
 257       /* Starting from binutils-2.23, the linker will define the
 258          magic symbol __ehdr_start to point to our own ELF header
 259          if it is visible in a segment that also includes the phdrs.
 260          So we can set up _dl_phdr and _dl_phnum even without any
 261          information from auxv.  */
 262
 263       extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
 264       assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
 265       _dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
 266       _dl_phnum = __ehdr_start.e_phnum;
 267     }
 268
 269   assert (_dl_phdr != NULL);
 270 }
 271 #endif
 272
 273
 274 void
 275 _dl_non_dynamic_init (void)
 276 {
 277   _dl_main_map.l_origin = _dl_get_origin ();
 278   _dl_main_map.l_phdr = GL(dl_phdr);
 279   _dl_main_map.l_phnum = GL(dl_phnum);
 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   if (__libc_enable_secure)
 289     {
 290       static const char unsecure_envvars[] =
 291         UNSECURE_ENVVARS
 292         ;
 293       const char *cp = unsecure_envvars;
 294
 295       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 296         {
 297           __unsetenv (cp);
 298           cp = strchr (cp, '\0') + 1;
 299         }
 300     }
 301
 302   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 303
 304   /* Initialize the data structures for the search paths for shared
 305      objects.  */
 306   _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
 307                   /* No glibc-hwcaps selection support in statically
 308                      linked binaries.  */
 309                   NULL, NULL);
 310
 311   /* Remember the last search directory added at startup.  */
 312   _dl_init_all_dirs = GL(dl_all_dirs);
 313
 314   _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 315
 316   _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
 317
 318   _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
 319
 320 #ifdef DL_PLATFORM_INIT
 321   DL_PLATFORM_INIT;
 322 #endif
 323
 324   /* Now determine the length of the platform string.  */
 325   if (_dl_platform != NULL)
 326     _dl_platformlen = strlen (_dl_platform);
 327
 328   for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 329     switch (ph->p_type)
 330       {
 331       /* Check if the stack is nonexecutable.  */
 332       case PT_GNU_STACK:
 333         _dl_stack_flags = ph->p_flags;
 334         break;
 335
 336       case PT_GNU_RELRO:
 337         _dl_main_map.l_relro_addr = ph->p_vaddr;
 338         _dl_main_map.l_relro_size = ph->p_memsz;
 339         break;
 340       }
 341
 342   call_function_static_weak (_dl_find_object_init);
 343
 344   /* Setup relro on the binary itself.  */
 345   if (_dl_main_map.l_relro_size != 0)
 346     _dl_protect_relro (&_dl_main_map);
 347 }
 348
 349 #ifdef DL_SYSINFO_IMPLEMENTATION
 350 DL_SYSINFO_IMPLEMENTATION
 351 #endif
 352
 353 /* Since relocation to hidden _dl_main_map causes relocation overflow on
 354    aarch64, a function is used to get the address of _dl_main_map.  */
 355
 356 struct link_map *
 357 _dl_get_dl_main_map (void)
 358 {
 359   return &_dl_main_map;
 360 }
 361
 362 /* This is used by _dl_runtime_profile, not used on static code.  */
 363 void
 364 DL_ARCH_FIXUP_ATTRIBUTE
 365 _dl_audit_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 366                    const void *inregs, void *outregs)
 367 {
 368 }