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
 162 enum dso_sort_algorithm _dl_dso_sort_algo;
 163
 164 /* The value of the FPU control word the kernel will preset in hardware.  */
 165 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 166
 167 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 168  * executable but this isn't true for all platforms.  */
 169 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
 170
 171 #if PTHREAD_IN_LIBC
 172 list_t _dl_stack_used;
 173 list_t _dl_stack_user;
 174 list_t _dl_stack_cache;
 175 size_t _dl_stack_cache_actsize;
 176 uintptr_t _dl_in_flight_stack;
 177 int _dl_stack_cache_lock;
 178 #else
 179 /* If loading a shared object requires that we make the stack executable
 180    when it was not, we do it by calling this function.
 181    It returns an errno code or zero on success.  */
 182 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 183 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 184 #endif
 185 struct dl_scope_free_list *_dl_scope_free_list;
 186
 187 #ifdef NEED_DL_SYSINFO
 188 /* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
 189    initialize it here to avoid RELATIVE relocation in static PIE.  */
 190 uintptr_t _dl_sysinfo;
 191 #endif
 192 #ifdef NEED_DL_SYSINFO_DSO
 193 /* Address of the ELF headers in the vsyscall page.  */
 194 const ElfW(Ehdr) *_dl_sysinfo_dso;
 195
 196 struct link_map *_dl_sysinfo_map;
 197
 198 # include "get-dynamic-info.h"
 199 #endif
 200 #include "setup-vdso.h"
 201 /* Define the vDSO function pointers.  */
 202 #include <dl-vdso-setup.c>
 203
 204 /* During the program run we must not modify the global data of
 205    loaded shared object simultaneously in two threads.  Therefore we
 206    protect `_dl_open' and `_dl_close' in dl-close.c.
 207
 208    This must be a recursive lock since the initializer function of
 209    the loaded object might as well require a call to this function.
 210    At this time it is not anymore a problem to modify the tables.  */
 211 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
 212 /* This lock is used to keep __dl_iterate_phdr from inspecting the
 213    list of loaded objects while an object is added to or removed from
 214    that list.  */
 215 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
 216   /* This lock protects global and module specific TLS related data.
 217      E.g. it is held in dlopen and dlclose when GL(dl_tls_generation),
 218      GL(dl_tls_max_dtv_idx) or GL(dl_tls_dtv_slotinfo_list) are
 219      accessed and when TLS related relocations are processed for a
 220      module.  It was introduced to keep pthread_create accessing TLS
 221      state that is being set up.  */
 222 __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
 223
 224
 225 #ifdef HAVE_AUX_VECTOR
 226 #include <dl-parse_auxv.h>
 227
 228 int _dl_clktck;
 229
 230 void
 231 _dl_aux_init (ElfW(auxv_t) *av)
 232 {
 233 #ifdef NEED_DL_SYSINFO
 234   /* NB: Avoid RELATIVE relocation in static PIE.  */
 235   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 236 #endif
 237
 238   _dl_auxv = av;
 239   dl_parse_auxv_t auxv_values;
 240   /* Use an explicit initialization loop here because memset may not
 241      be available yet.  */
 242   for (int i = 0; i < array_length (auxv_values); ++i)
 243     auxv_values[i] = 0;
 244   _dl_parse_auxv (av, auxv_values);
 245
 246   _dl_phdr = (void*) auxv_values[AT_PHDR];
 247   _dl_phnum = auxv_values[AT_PHNUM];
 248
 249   if (_dl_phdr == NULL)
 250     {
 251       /* Starting from binutils-2.23, the linker will define the
 252          magic symbol __ehdr_start to point to our own ELF header
 253          if it is visible in a segment that also includes the phdrs.
 254          So we can set up _dl_phdr and _dl_phnum even without any
 255          information from auxv.  */
 256
 257       extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
 258       assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
 259       _dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
 260       _dl_phnum = __ehdr_start.e_phnum;
 261     }
 262
 263   assert (_dl_phdr != NULL);
 264 }
 265 #endif
 266
 267
 268 void
 269 _dl_non_dynamic_init (void)
 270 {
 271   _dl_main_map.l_origin = _dl_get_origin ();
 272   _dl_main_map.l_phdr = GL(dl_phdr);
 273   _dl_main_map.l_phnum = GL(dl_phnum);
 274
 275   /* Set up the data structures for the system-supplied DSO early,
 276      so they can influence _dl_init_paths.  */
 277   setup_vdso (NULL, NULL);
 278
 279   /* With vDSO setup we can initialize the function pointers.  */
 280   setup_vdso_pointers ();
 281
 282   if (__libc_enable_secure)
 283     {
 284       static const char unsecure_envvars[] =
 285         UNSECURE_ENVVARS
 286         ;
 287       const char *cp = unsecure_envvars;
 288
 289       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 290         {
 291           __unsetenv (cp);
 292           cp = strchr (cp, '\0') + 1;
 293         }
 294     }
 295
 296   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 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 #ifdef DL_PLATFORM_INIT
 315   DL_PLATFORM_INIT;
 316 #endif
 317
 318   /* Now determine the length of the platform string.  */
 319   if (_dl_platform != NULL)
 320     _dl_platformlen = strlen (_dl_platform);
 321
 322   for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 323     switch (ph->p_type)
 324       {
 325       /* Check if the stack is nonexecutable.  */
 326       case PT_GNU_STACK:
 327         _dl_stack_flags = ph->p_flags;
 328         break;
 329
 330       case PT_GNU_RELRO:
 331         _dl_main_map.l_relro_addr = ph->p_vaddr;
 332         _dl_main_map.l_relro_size = ph->p_memsz;
 333         break;
 334       }
 335
 336   call_function_static_weak (_dl_find_object_init);
 337
 338   /* Setup relro on the binary itself.  */
 339   if (_dl_main_map.l_relro_size != 0)
 340     _dl_protect_relro (&_dl_main_map);
 341 }
 342
 343 #ifdef DL_SYSINFO_IMPLEMENTATION
 344 DL_SYSINFO_IMPLEMENTATION
 345 #endif
 346
 347 /* Since relocation to hidden _dl_main_map causes relocation overflow on
 348    aarch64, a function is used to get the address of _dl_main_map.  */
 349
 350 struct link_map *
 351 _dl_get_dl_main_map (void)
 352 {
 353   return &_dl_main_map;
 354 }
 355
 356 /* This is used by _dl_runtime_profile, not used on static code.  */
 357 void
 358 DL_ARCH_FIXUP_ATTRIBUTE
 359 _dl_audit_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 360                    const void *inregs, void *outregs)
 361 {
 362 }