elf/dl-support.c

   1 /* Support for dynamic linking code in static libc.
   2    Copyright (C) 1996-2021 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-librecon.h>
  39 #include <dl-procinfo.h>
  40 #include <unsecvars.h>
  41 #include <hp-timing.h>
  42 #include <stackinfo.h>
  43 #include <dl-vdso.h>
  44 #include <dl-vdso-setup.h>
  45 #include <dl-auxv.h>
  46
  47 extern char *__progname;
  48 char **_dl_argv = &__progname;  /* This is checked for some error messages.  */
  49
  50 /* Name of the architecture.  */
  51 const char *_dl_platform;
  52 size_t _dl_platformlen;
  53
  54 int _dl_debug_mask;
  55 int _dl_lazy;
  56 ElfW(Addr) _dl_use_load_bias = -2;
  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 unsigned int _dl_osversion;
 148
 149 /* All known directories in sorted order.  */
 150 struct r_search_path_elem *_dl_all_dirs;
 151
 152 /* All directories after startup.  */
 153 struct r_search_path_elem *_dl_init_all_dirs;
 154
 155 /* The object to be initialized first.  */
 156 struct link_map *_dl_initfirst;
 157
 158 /* Descriptor to write debug messages to.  */
 159 int _dl_debug_fd = STDERR_FILENO;
 160
 161 int _dl_correct_cache_id = _DL_CACHE_DEFAULT_ID;
 162
 163 ElfW(auxv_t) *_dl_auxv;
 164 const ElfW(Phdr) *_dl_phdr;
 165 size_t _dl_phnum;
 166 uint64_t _dl_hwcap;
 167 uint64_t _dl_hwcap2;
 168
 169 enum dso_sort_algorithm _dl_dso_sort_algo;
 170
 171 /* The value of the FPU control word the kernel will preset in hardware.  */
 172 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 173
 174 #if !HAVE_TUNABLES
 175 /* This is not initialized to HWCAP_IMPORTANT, matching the definition
 176    of _dl_important_hwcaps, below, where no hwcap strings are ever
 177    used.  This mask is still used to mediate the lookups in the cache
 178    file.  Since there is no way to set this nonzero (we don't grok the
 179    LD_HWCAP_MASK environment variable here), there is no real point in
 180    setting _dl_hwcap nonzero below, but we do anyway.  */
 181 uint64_t _dl_hwcap_mask;
 182 #endif
 183
 184 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 185  * executable but this isn't true for all platforms.  */
 186 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
 187
 188 #if PTHREAD_IN_LIBC
 189 list_t _dl_stack_used;
 190 list_t _dl_stack_user;
 191 list_t _dl_stack_cache;
 192 size_t _dl_stack_cache_actsize;
 193 uintptr_t _dl_in_flight_stack;
 194 int _dl_stack_cache_lock;
 195 #else
 196 /* If loading a shared object requires that we make the stack executable
 197    when it was not, we do it by calling this function.
 198    It returns an errno code or zero on success.  */
 199 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 200 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 201 #endif
 202 struct dl_scope_free_list *_dl_scope_free_list;
 203
 204 #ifdef NEED_DL_SYSINFO
 205 /* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
 206    initialize it here to avoid RELATIVE relocation in static PIE.  */
 207 uintptr_t _dl_sysinfo;
 208 #endif
 209 #ifdef NEED_DL_SYSINFO_DSO
 210 /* Address of the ELF headers in the vsyscall page.  */
 211 const ElfW(Ehdr) *_dl_sysinfo_dso;
 212
 213 struct link_map *_dl_sysinfo_map;
 214
 215 # include "get-dynamic-info.h"
 216 #endif
 217 #include "setup-vdso.h"
 218 /* Define the vDSO function pointers.  */
 219 #include <dl-vdso-setup.c>
 220
 221 /* During the program run we must not modify the global data of
 222    loaded shared object simultanously in two threads.  Therefore we
 223    protect `_dl_open' and `_dl_close' in dl-close.c.
 224
 225    This must be a recursive lock since the initializer function of
 226    the loaded object might as well require a call to this function.
 227    At this time it is not anymore a problem to modify the tables.  */
 228 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
 229 /* This lock is used to keep __dl_iterate_phdr from inspecting the
 230    list of loaded objects while an object is added to or removed from
 231    that list.  */
 232 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
 233   /* This lock protects global and module specific TLS related data.
 234      E.g. it is held in dlopen and dlclose when GL(dl_tls_generation),
 235      GL(dl_tls_max_dtv_idx) or GL(dl_tls_dtv_slotinfo_list) are
 236      accessed and when TLS related relocations are processed for a
 237      module.  It was introduced to keep pthread_create accessing TLS
 238      state that is being set up.  */
 239 __rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)
 240
 241
 242 #ifdef HAVE_AUX_VECTOR
 243 int _dl_clktck;
 244
 245 void
 246 _dl_aux_init (ElfW(auxv_t) *av)
 247 {
 248   int seen = 0;
 249   uid_t uid = 0;
 250   gid_t gid = 0;
 251
 252 #ifdef NEED_DL_SYSINFO
 253   /* NB: Avoid RELATIVE relocation in static PIE.  */
 254   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 255 #endif
 256
 257   _dl_auxv = av;
 258   for (; av->a_type != AT_NULL; ++av)
 259     switch (av->a_type)
 260       {
 261       case AT_PAGESZ:
 262         if (av->a_un.a_val != 0)
 263           GLRO(dl_pagesize) = av->a_un.a_val;
 264         break;
 265       case AT_CLKTCK:
 266         GLRO(dl_clktck) = av->a_un.a_val;
 267         break;
 268       case AT_PHDR:
 269         GL(dl_phdr) = (const void *) av->a_un.a_val;
 270         break;
 271       case AT_PHNUM:
 272         GL(dl_phnum) = av->a_un.a_val;
 273         break;
 274       case AT_PLATFORM:
 275         GLRO(dl_platform) = (void *) av->a_un.a_val;
 276         break;
 277       case AT_HWCAP:
 278         GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
 279         break;
 280       case AT_HWCAP2:
 281         GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
 282         break;
 283       case AT_FPUCW:
 284         GLRO(dl_fpu_control) = av->a_un.a_val;
 285         break;
 286 #ifdef NEED_DL_SYSINFO
 287       case AT_SYSINFO:
 288         GL(dl_sysinfo) = av->a_un.a_val;
 289         break;
 290 #endif
 291 #ifdef NEED_DL_SYSINFO_DSO
 292       case AT_SYSINFO_EHDR:
 293         GL(dl_sysinfo_dso) = (void *) av->a_un.a_val;
 294         break;
 295 #endif
 296       case AT_UID:
 297         uid ^= av->a_un.a_val;
 298         seen |= 1;
 299         break;
 300       case AT_EUID:
 301         uid ^= av->a_un.a_val;
 302         seen |= 2;
 303         break;
 304       case AT_GID:
 305         gid ^= av->a_un.a_val;
 306         seen |= 4;
 307         break;
 308       case AT_EGID:
 309         gid ^= av->a_un.a_val;
 310         seen |= 8;
 311         break;
 312       case AT_SECURE:
 313         seen = -1;
 314         __libc_enable_secure = av->a_un.a_val;
 315         __libc_enable_secure_decided = 1;
 316         break;
 317       case AT_RANDOM:
 318         _dl_random = (void *) av->a_un.a_val;
 319         break;
 320       case AT_MINSIGSTKSZ:
 321         _dl_minsigstacksize = av->a_un.a_val;
 322         break;
 323       DL_PLATFORM_AUXV
 324       }
 325   if (seen == 0xf)
 326     {
 327       __libc_enable_secure = uid != 0 || gid != 0;
 328       __libc_enable_secure_decided = 1;
 329     }
 330 }
 331 #endif
 332
 333
 334 void
 335 _dl_non_dynamic_init (void)
 336 {
 337   _dl_main_map.l_origin = _dl_get_origin ();
 338   _dl_main_map.l_phdr = GL(dl_phdr);
 339   _dl_main_map.l_phnum = GL(dl_phnum);
 340
 341   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 342
 343   /* Set up the data structures for the system-supplied DSO early,
 344      so they can influence _dl_init_paths.  */
 345   setup_vdso (NULL, NULL);
 346
 347   /* With vDSO setup we can initialize the function pointers.  */
 348   setup_vdso_pointers ();
 349
 350   /* Initialize the data structures for the search paths for shared
 351      objects.  */
 352   _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
 353                   /* No glibc-hwcaps selection support in statically
 354                      linked binaries.  */
 355                   NULL, NULL);
 356
 357   /* Remember the last search directory added at startup.  */
 358   _dl_init_all_dirs = GL(dl_all_dirs);
 359
 360   _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 361
 362   _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
 363
 364   _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
 365
 366   _dl_profile_output = getenv ("LD_PROFILE_OUTPUT");
 367   if (_dl_profile_output == NULL || _dl_profile_output[0] == '\0')
 368     _dl_profile_output
 369       = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];
 370
 371   if (__libc_enable_secure)
 372     {
 373       static const char unsecure_envvars[] =
 374         UNSECURE_ENVVARS
 375 #ifdef EXTRA_UNSECURE_ENVVARS
 376         EXTRA_UNSECURE_ENVVARS
 377 #endif
 378         ;
 379       const char *cp = unsecure_envvars;
 380
 381       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 382         {
 383           __unsetenv (cp);
 384           cp = (const char *) __rawmemchr (cp, '\0') + 1;
 385         }
 386
 387 #if !HAVE_TUNABLES
 388       if (__access ("/etc/suid-debug", F_OK) != 0)
 389         __unsetenv ("MALLOC_CHECK_");
 390 #endif
 391     }
 392
 393 #ifdef DL_PLATFORM_INIT
 394   DL_PLATFORM_INIT;
 395 #endif
 396
 397 #ifdef DL_OSVERSION_INIT
 398   DL_OSVERSION_INIT;
 399 #endif
 400
 401   /* Now determine the length of the platform string.  */
 402   if (_dl_platform != NULL)
 403     _dl_platformlen = strlen (_dl_platform);
 404
 405   if (_dl_phdr != NULL)
 406     for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 407       switch (ph->p_type)
 408         {
 409         /* Check if the stack is nonexecutable.  */
 410         case PT_GNU_STACK:
 411           _dl_stack_flags = ph->p_flags;
 412           break;
 413
 414         case PT_GNU_RELRO:
 415           _dl_main_map.l_relro_addr = ph->p_vaddr;
 416           _dl_main_map.l_relro_size = ph->p_memsz;
 417           break;
 418         }
 419
 420   /* Setup relro on the binary itself.  */
 421   if (_dl_main_map.l_relro_size != 0)
 422     _dl_protect_relro (&_dl_main_map);
 423 }
 424
 425 #ifdef DL_SYSINFO_IMPLEMENTATION
 426 DL_SYSINFO_IMPLEMENTATION
 427 #endif
 428
 429 #if ENABLE_STATIC_PIE
 430 /* Since relocation to hidden _dl_main_map causes relocation overflow on
 431    aarch64, a function is used to get the address of _dl_main_map.  */
 432
 433 struct link_map *
 434 _dl_get_dl_main_map (void)
 435 {
 436   return &_dl_main_map;
 437 }
 438 #endif