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 = EXEC_PAGESIZE;
 139
 140 size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;
 141
 142 int _dl_inhibit_cache;
 143
 144 /* All known directories in sorted order.  */
 145 struct r_search_path_elem *_dl_all_dirs;
 146
 147 /* All directories after startup.  */
 148 struct r_search_path_elem *_dl_init_all_dirs;
 149
 150 /* The object to be initialized first.  */
 151 struct link_map *_dl_initfirst;
 152
 153 /* Descriptor to write debug messages to.  */
 154 int _dl_debug_fd = STDERR_FILENO;
 155
 156 ElfW(auxv_t) *_dl_auxv;
 157 const ElfW(Phdr) *_dl_phdr;
 158 size_t _dl_phnum;
 159 uint64_t _dl_hwcap;
 160 uint64_t _dl_hwcap2;
 161 uint64_t _dl_hwcap3;
 162 uint64_t _dl_hwcap4;
 163
 164 enum dso_sort_algorithm _dl_dso_sort_algo;
 165
 166 /* The value of the FPU control word the kernel will preset in hardware.  */
 167 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 168
 169 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 170  * executable but this isn't true for all platforms.  */
 171 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
 172
 173 #if PTHREAD_IN_LIBC
 174 list_t _dl_stack_used;
 175 list_t _dl_stack_user;
 176 list_t _dl_stack_cache;
 177 size_t _dl_stack_cache_actsize;
 178 uintptr_t _dl_in_flight_stack;
 179 int _dl_stack_cache_lock;
 180 #else
 181 /* If loading a shared object requires that we make the stack executable
 182    when it was not, we do it by calling this function.
 183    It returns an errno code or zero on success.  */
 184 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 185 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 186 #endif
 187 struct dl_scope_free_list *_dl_scope_free_list;
 188
 189 #ifdef NEED_DL_SYSINFO
 190 /* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
 191    initialize it here to avoid RELATIVE relocation in static PIE.  */
 192 uintptr_t _dl_sysinfo;
 193 #endif
 194 #ifdef NEED_DL_SYSINFO_DSO
 195 /* Address of the ELF headers in the vsyscall page.  */
 196 const ElfW(Ehdr) *_dl_sysinfo_dso;
 197
 198 struct link_map *_dl_sysinfo_map;
 199
 200 # include "get-dynamic-info.h"
 201 #endif
 202 #include "setup-vdso.h"
 203 /* Define the vDSO function pointers.  */
 204 #include <dl-vdso-setup.c>
 205
 206 /* During the program run we must not modify the global data of
 207    loaded shared object simultaneously in two threads.  Therefore we
 208    protect `_dl_open' and `_dl_close' in dl-close.c.
 209
 210    This must be a recursive lock since the initializer function of
 211    the loaded object might as well require a call to this function.
 212    At this time it is not anymore a problem to modify the tables.  */
 213 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
 214 /* This lock is used to keep __dl_iterate_phdr from inspecting the
 215    list of loaded objects while an object is added to or removed from
 216    that list.  */
 217 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
 218   /* This lock protects global and module specific TLS related data.
 219      E.g. it is held in dlopen and dlclose when GL(dl_tls_generation),
 220      GL(dl_tls_max_dtv_idx) or GL(dl_tls_dtv_slotinfo_list) are
 221      accessed and when TLS related relocations are processed for a
 222      module.  It was introduced to keep pthread_create accessing TLS
 223      state that is being set up.  */
 224 __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
 225
 226
 227 #ifdef HAVE_AUX_VECTOR
 228 #include <dl-parse_auxv.h>
 229
 230 int _dl_clktck;
 231
 232 void
 233 _dl_aux_init (ElfW(auxv_t) *av)
 234 {
 235 #ifdef NEED_DL_SYSINFO
 236   /* NB: Avoid RELATIVE relocation in static PIE.  */
 237   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 238 #endif
 239
 240   _dl_auxv = av;
 241   dl_parse_auxv_t auxv_values;
 242   /* Use an explicit initialization loop here because memset may not
 243      be available yet.  */
 244   for (int i = 0; i < array_length (auxv_values); ++i)
 245     auxv_values[i] = 0;
 246   _dl_parse_auxv (av, auxv_values);
 247
 248   _dl_phdr = (void*) auxv_values[AT_PHDR];
 249   _dl_phnum = auxv_values[AT_PHNUM];
 250
 251   if (_dl_phdr == NULL)
 252     {
 253       /* Starting from binutils-2.23, the linker will define the
 254          magic symbol __ehdr_start to point to our own ELF header
 255          if it is visible in a segment that also includes the phdrs.
 256          So we can set up _dl_phdr and _dl_phnum even without any
 257          information from auxv.  */
 258
 259       extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
 260       assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
 261       _dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
 262       _dl_phnum = __ehdr_start.e_phnum;
 263     }
 264
 265   assert (_dl_phdr != NULL);
 266 }
 267 #endif
 268
 269
 270 void
 271 _dl_non_dynamic_init (void)
 272 {
 273   _dl_main_map.l_origin = _dl_get_origin ();
 274   _dl_main_map.l_phdr = GL(dl_phdr);
 275   _dl_main_map.l_phnum = GL(dl_phnum);
 276
 277   /* Set up the data structures for the system-supplied DSO early,
 278      so they can influence _dl_init_paths.  */
 279   setup_vdso (NULL, NULL);
 280
 281   /* With vDSO setup we can initialize the function pointers.  */
 282   setup_vdso_pointers ();
 283
 284   if (__libc_enable_secure)
 285     {
 286       static const char unsecure_envvars[] =
 287         UNSECURE_ENVVARS
 288         ;
 289       const char *cp = unsecure_envvars;
 290
 291       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 292         {
 293           __unsetenv (cp);
 294           cp = strchr (cp, '\0') + 1;
 295         }
 296     }
 297
 298   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 299
 300   /* Initialize the data structures for the search paths for shared
 301      objects.  */
 302   _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
 303                   /* No glibc-hwcaps selection support in statically
 304                      linked binaries.  */
 305                   NULL, NULL);
 306
 307   /* Remember the last search directory added at startup.  */
 308   _dl_init_all_dirs = GL(dl_all_dirs);
 309
 310   _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 311
 312   _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
 313
 314   _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
 315
 316 #ifdef DL_PLATFORM_INIT
 317   DL_PLATFORM_INIT;
 318 #endif
 319
 320   /* Now determine the length of the platform string.  */
 321   if (_dl_platform != NULL)
 322     _dl_platformlen = strlen (_dl_platform);
 323
 324   for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 325     switch (ph->p_type)
 326       {
 327       /* Check if the stack is nonexecutable.  */
 328       case PT_GNU_STACK:
 329         _dl_stack_flags = ph->p_flags;
 330         break;
 331
 332       case PT_GNU_RELRO:
 333         _dl_main_map.l_relro_addr = ph->p_vaddr;
 334         _dl_main_map.l_relro_size = ph->p_memsz;
 335         break;
 336       }
 337
 338   call_function_static_weak (_dl_find_object_init);
 339
 340   /* Setup relro on the binary itself.  */
 341   if (_dl_main_map.l_relro_size != 0)
 342     _dl_protect_relro (&_dl_main_map);
 343 }
 344
 345 #ifdef DL_SYSINFO_IMPLEMENTATION
 346 DL_SYSINFO_IMPLEMENTATION
 347 #endif
 348
 349 /* Since relocation to hidden _dl_main_map causes relocation overflow on
 350    aarch64, a function is used to get the address of _dl_main_map.  */
 351
 352 struct link_map *
 353 _dl_get_dl_main_map (void)
 354 {
 355   return &_dl_main_map;
 356 }
 357
 358 /* This is used by _dl_runtime_profile, not used on static code.  */
 359 void
 360 DL_ARCH_FIXUP_ATTRIBUTE
 361 _dl_audit_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 362                    const void *inregs, void *outregs)
 363 {
 364 }