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 #if !HAVE_TUNABLES
 172 /* This is not initialized to HWCAP_IMPORTANT, matching the definition
 173    of _dl_important_hwcaps, below, where no hwcap strings are ever
 174    used.  This mask is still used to mediate the lookups in the cache
 175    file.  Since there is no way to set this nonzero (we don't grok the
 176    LD_HWCAP_MASK environment variable here), there is no real point in
 177    setting _dl_hwcap nonzero below, but we do anyway.  */
 178 uint64_t _dl_hwcap_mask;
 179 #endif
 180
 181 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 182  * executable but this isn't true for all platforms.  */
 183 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
 184
 185 #if PTHREAD_IN_LIBC
 186 list_t _dl_stack_used;
 187 list_t _dl_stack_user;
 188 list_t _dl_stack_cache;
 189 size_t _dl_stack_cache_actsize;
 190 uintptr_t _dl_in_flight_stack;
 191 int _dl_stack_cache_lock;
 192 #else
 193 /* If loading a shared object requires that we make the stack executable
 194    when it was not, we do it by calling this function.
 195    It returns an errno code or zero on success.  */
 196 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 197 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 198 #endif
 199 struct dl_scope_free_list *_dl_scope_free_list;
 200
 201 #ifdef NEED_DL_SYSINFO
 202 /* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
 203    initialize it here to avoid RELATIVE relocation in static PIE.  */
 204 uintptr_t _dl_sysinfo;
 205 #endif
 206 #ifdef NEED_DL_SYSINFO_DSO
 207 /* Address of the ELF headers in the vsyscall page.  */
 208 const ElfW(Ehdr) *_dl_sysinfo_dso;
 209
 210 struct link_map *_dl_sysinfo_map;
 211
 212 # include "get-dynamic-info.h"
 213 #endif
 214 #include "setup-vdso.h"
 215 /* Define the vDSO function pointers.  */
 216 #include <dl-vdso-setup.c>
 217
 218 /* During the program run we must not modify the global data of
 219    loaded shared object simultanously in two threads.  Therefore we
 220    protect `_dl_open' and `_dl_close' in dl-close.c.
 221
 222    This must be a recursive lock since the initializer function of
 223    the loaded object might as well require a call to this function.
 224    At this time it is not anymore a problem to modify the tables.  */
 225 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
 226 /* This lock is used to keep __dl_iterate_phdr from inspecting the
 227    list of loaded objects while an object is added to or removed from
 228    that list.  */
 229 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
 230   /* This lock protects global and module specific TLS related data.
 231      E.g. it is held in dlopen and dlclose when GL(dl_tls_generation),
 232      GL(dl_tls_max_dtv_idx) or GL(dl_tls_dtv_slotinfo_list) are
 233      accessed and when TLS related relocations are processed for a
 234      module.  It was introduced to keep pthread_create accessing TLS
 235      state that is being set up.  */
 236 __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
 237
 238
 239 #ifdef HAVE_AUX_VECTOR
 240 #include <dl-parse_auxv.h>
 241
 242 int _dl_clktck;
 243
 244 void
 245 _dl_aux_init (ElfW(auxv_t) *av)
 246 {
 247 #ifdef NEED_DL_SYSINFO
 248   /* NB: Avoid RELATIVE relocation in static PIE.  */
 249   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 250 #endif
 251
 252   _dl_auxv = av;
 253   dl_parse_auxv_t auxv_values;
 254   /* Use an explicit initialization loop here because memset may not
 255      be available yet.  */
 256   for (int i = 0; i < array_length (auxv_values); ++i)
 257     auxv_values[i] = 0;
 258   _dl_parse_auxv (av, auxv_values);
 259
 260   _dl_phdr = (void*) auxv_values[AT_PHDR];
 261   _dl_phnum = auxv_values[AT_PHNUM];
 262
 263   if (_dl_phdr == NULL)
 264     {
 265       /* Starting from binutils-2.23, the linker will define the
 266          magic symbol __ehdr_start to point to our own ELF header
 267          if it is visible in a segment that also includes the phdrs.
 268          So we can set up _dl_phdr and _dl_phnum even without any
 269          information from auxv.  */
 270
 271       extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
 272       assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
 273       _dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
 274       _dl_phnum = __ehdr_start.e_phnum;
 275     }
 276
 277   assert (_dl_phdr != NULL);
 278 }
 279 #endif
 280
 281
 282 void
 283 _dl_non_dynamic_init (void)
 284 {
 285   _dl_main_map.l_origin = _dl_get_origin ();
 286   _dl_main_map.l_phdr = GL(dl_phdr);
 287   _dl_main_map.l_phnum = GL(dl_phnum);
 288
 289   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 290
 291   /* Set up the data structures for the system-supplied DSO early,
 292      so they can influence _dl_init_paths.  */
 293   setup_vdso (NULL, NULL);
 294
 295   /* With vDSO setup we can initialize the function pointers.  */
 296   setup_vdso_pointers ();
 297
 298   /* Initialize the data structures for the search paths for shared
 299      objects.  */
 300   _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
 301                   /* No glibc-hwcaps selection support in statically
 302                      linked binaries.  */
 303                   NULL, NULL);
 304
 305   /* Remember the last search directory added at startup.  */
 306   _dl_init_all_dirs = GL(dl_all_dirs);
 307
 308   _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 309
 310   _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
 311
 312   _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
 313
 314   _dl_profile_output = getenv ("LD_PROFILE_OUTPUT");
 315   if (_dl_profile_output == NULL || _dl_profile_output[0] == '\0')
 316     _dl_profile_output
 317       = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];
 318
 319   if (__libc_enable_secure)
 320     {
 321       static const char unsecure_envvars[] =
 322         UNSECURE_ENVVARS
 323         ;
 324       const char *cp = unsecure_envvars;
 325
 326       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 327         {
 328           __unsetenv (cp);
 329           cp = (const char *) __rawmemchr (cp, '\0') + 1;
 330         }
 331
 332 #if !HAVE_TUNABLES
 333       if (__access ("/etc/suid-debug", F_OK) != 0)
 334         __unsetenv ("MALLOC_CHECK_");
 335 #endif
 336     }
 337
 338 #ifdef DL_PLATFORM_INIT
 339   DL_PLATFORM_INIT;
 340 #endif
 341
 342   /* Now determine the length of the platform string.  */
 343   if (_dl_platform != NULL)
 344     _dl_platformlen = strlen (_dl_platform);
 345
 346   for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 347     switch (ph->p_type)
 348       {
 349       /* Check if the stack is nonexecutable.  */
 350       case PT_GNU_STACK:
 351         _dl_stack_flags = ph->p_flags;
 352         break;
 353
 354       case PT_GNU_RELRO:
 355         _dl_main_map.l_relro_addr = ph->p_vaddr;
 356         _dl_main_map.l_relro_size = ph->p_memsz;
 357         break;
 358       }
 359
 360   call_function_static_weak (_dl_find_object_init);
 361
 362   /* Setup relro on the binary itself.  */
 363   if (_dl_main_map.l_relro_size != 0)
 364     _dl_protect_relro (&_dl_main_map);
 365 }
 366
 367 #ifdef DL_SYSINFO_IMPLEMENTATION
 368 DL_SYSINFO_IMPLEMENTATION
 369 #endif
 370
 371 #if ENABLE_STATIC_PIE
 372 /* Since relocation to hidden _dl_main_map causes relocation overflow on
 373    aarch64, a function is used to get the address of _dl_main_map.  */
 374
 375 struct link_map *
 376 _dl_get_dl_main_map (void)
 377 {
 378   return &_dl_main_map;
 379 }
 380 #endif
 381
 382 /* This is used by _dl_runtime_profile, not used on static code.  */
 383 void
 384 DL_ARCH_FIXUP_ATTRIBUTE
 385 _dl_audit_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 386                    const void *inregs, void *outregs)
 387 {
 388 }