elf/dl-support.c

   1 /* Support for dynamic linking code in static libc.
   2    Copyright (C) 1996-2022 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
  48 extern char *__progname;
  49 char **_dl_argv = &__progname;  /* This is checked for some error messages.  */
  50
  51 /* Name of the architecture.  */
  52 const char *_dl_platform;
  53 size_t _dl_platformlen;
  54
  55 int _dl_debug_mask;
  56 int _dl_lazy;
  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 /* All known directories in sorted order.  */
 148 struct r_search_path_elem *_dl_all_dirs;
 149
 150 /* All directories after startup.  */
 151 struct r_search_path_elem *_dl_init_all_dirs;
 152
 153 /* The object to be initialized first.  */
 154 struct link_map *_dl_initfirst;
 155
 156 /* Descriptor to write debug messages to.  */
 157 int _dl_debug_fd = STDERR_FILENO;
 158
 159 ElfW(auxv_t) *_dl_auxv;
 160 const ElfW(Phdr) *_dl_phdr;
 161 size_t _dl_phnum;
 162 uint64_t _dl_hwcap;
 163 uint64_t _dl_hwcap2;
 164
 165 enum dso_sort_algorithm _dl_dso_sort_algo;
 166
 167 /* The value of the FPU control word the kernel will preset in hardware.  */
 168 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 169
 170 #if !HAVE_TUNABLES
 171 /* This is not initialized to HWCAP_IMPORTANT, matching the definition
 172    of _dl_important_hwcaps, below, where no hwcap strings are ever
 173    used.  This mask is still used to mediate the lookups in the cache
 174    file.  Since there is no way to set this nonzero (we don't grok the
 175    LD_HWCAP_MASK environment variable here), there is no real point in
 176    setting _dl_hwcap nonzero below, but we do anyway.  */
 177 uint64_t _dl_hwcap_mask;
 178 #endif
 179
 180 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 181  * executable but this isn't true for all platforms.  */
 182 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
 183
 184 #if PTHREAD_IN_LIBC
 185 list_t _dl_stack_used;
 186 list_t _dl_stack_user;
 187 list_t _dl_stack_cache;
 188 size_t _dl_stack_cache_actsize;
 189 uintptr_t _dl_in_flight_stack;
 190 int _dl_stack_cache_lock;
 191 #else
 192 /* If loading a shared object requires that we make the stack executable
 193    when it was not, we do it by calling this function.
 194    It returns an errno code or zero on success.  */
 195 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 196 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 197 #endif
 198 struct dl_scope_free_list *_dl_scope_free_list;
 199
 200 #ifdef NEED_DL_SYSINFO
 201 /* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
 202    initialize it here to avoid RELATIVE relocation in static PIE.  */
 203 uintptr_t _dl_sysinfo;
 204 #endif
 205 #ifdef NEED_DL_SYSINFO_DSO
 206 /* Address of the ELF headers in the vsyscall page.  */
 207 const ElfW(Ehdr) *_dl_sysinfo_dso;
 208
 209 struct link_map *_dl_sysinfo_map;
 210
 211 # include "get-dynamic-info.h"
 212 #endif
 213 #include "setup-vdso.h"
 214 /* Define the vDSO function pointers.  */
 215 #include <dl-vdso-setup.c>
 216
 217 /* During the program run we must not modify the global data of
 218    loaded shared object simultanously in two threads.  Therefore we
 219    protect `_dl_open' and `_dl_close' in dl-close.c.
 220
 221    This must be a recursive lock since the initializer function of
 222    the loaded object might as well require a call to this function.
 223    At this time it is not anymore a problem to modify the tables.  */
 224 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
 225 /* This lock is used to keep __dl_iterate_phdr from inspecting the
 226    list of loaded objects while an object is added to or removed from
 227    that list.  */
 228 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
 229   /* This lock protects global and module specific TLS related data.
 230      E.g. it is held in dlopen and dlclose when GL(dl_tls_generation),
 231      GL(dl_tls_max_dtv_idx) or GL(dl_tls_dtv_slotinfo_list) are
 232      accessed and when TLS related relocations are processed for a
 233      module.  It was introduced to keep pthread_create accessing TLS
 234      state that is being set up.  */
 235 __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
 236
 237
 238 #ifdef HAVE_AUX_VECTOR
 239 #include <dl-parse_auxv.h>
 240
 241 int _dl_clktck;
 242
 243 void
 244 _dl_aux_init (ElfW(auxv_t) *av)
 245 {
 246 #ifdef NEED_DL_SYSINFO
 247   /* NB: Avoid RELATIVE relocation in static PIE.  */
 248   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 249 #endif
 250
 251   _dl_auxv = av;
 252   dl_parse_auxv_t auxv_values;
 253   /* Use an explicit initialization loop here because memset may not
 254      be available yet.  */
 255   for (int i = 0; i < array_length (auxv_values); ++i)
 256     auxv_values[i] = 0;
 257   _dl_parse_auxv (av, auxv_values);
 258 }
 259 #endif
 260
 261
 262 void
 263 _dl_non_dynamic_init (void)
 264 {
 265   _dl_main_map.l_origin = _dl_get_origin ();
 266   _dl_main_map.l_phdr = GL(dl_phdr);
 267   _dl_main_map.l_phnum = GL(dl_phnum);
 268
 269   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 270
 271   /* Set up the data structures for the system-supplied DSO early,
 272      so they can influence _dl_init_paths.  */
 273   setup_vdso (NULL, NULL);
 274
 275   /* With vDSO setup we can initialize the function pointers.  */
 276   setup_vdso_pointers ();
 277
 278   /* Initialize the data structures for the search paths for shared
 279      objects.  */
 280   _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
 281                   /* No glibc-hwcaps selection support in statically
 282                      linked binaries.  */
 283                   NULL, NULL);
 284
 285   /* Remember the last search directory added at startup.  */
 286   _dl_init_all_dirs = GL(dl_all_dirs);
 287
 288   _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 289
 290   _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
 291
 292   _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
 293
 294   _dl_profile_output = getenv ("LD_PROFILE_OUTPUT");
 295   if (_dl_profile_output == NULL || _dl_profile_output[0] == '\0')
 296     _dl_profile_output
 297       = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];
 298
 299   if (__libc_enable_secure)
 300     {
 301       static const char unsecure_envvars[] =
 302         UNSECURE_ENVVARS
 303         ;
 304       const char *cp = unsecure_envvars;
 305
 306       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 307         {
 308           __unsetenv (cp);
 309           cp = (const char *) __rawmemchr (cp, '\0') + 1;
 310         }
 311
 312 #if !HAVE_TUNABLES
 313       if (__access ("/etc/suid-debug", F_OK) != 0)
 314         __unsetenv ("MALLOC_CHECK_");
 315 #endif
 316     }
 317
 318 #ifdef DL_PLATFORM_INIT
 319   DL_PLATFORM_INIT;
 320 #endif
 321
 322   /* Now determine the length of the platform string.  */
 323   if (_dl_platform != NULL)
 324     _dl_platformlen = strlen (_dl_platform);
 325
 326   if (_dl_phdr != NULL)
 327     for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 328       switch (ph->p_type)
 329         {
 330         /* Check if the stack is nonexecutable.  */
 331         case PT_GNU_STACK:
 332           _dl_stack_flags = ph->p_flags;
 333           break;
 334
 335         case PT_GNU_RELRO:
 336           _dl_main_map.l_relro_addr = ph->p_vaddr;
 337           _dl_main_map.l_relro_size = ph->p_memsz;
 338           break;
 339         }
 340
 341   call_function_static_weak (_dl_find_object_init);
 342
 343   /* Setup relro on the binary itself.  */
 344   if (_dl_main_map.l_relro_size != 0)
 345     _dl_protect_relro (&_dl_main_map);
 346 }
 347
 348 #ifdef DL_SYSINFO_IMPLEMENTATION
 349 DL_SYSINFO_IMPLEMENTATION
 350 #endif
 351
 352 #if ENABLE_STATIC_PIE
 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 #endif
 362
 363 /* This is used by _dl_runtime_profile, not used on static code.  */
 364 void
 365 DL_ARCH_FIXUP_ATTRIBUTE
 366 _dl_audit_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 367                    const void *inregs, void *outregs)
 368 {
 369 }