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 void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
 142
 143 size_t _dl_pagesize = EXEC_PAGESIZE;
 144
 145 size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;
 146
 147 int _dl_inhibit_cache;
 148
 149 unsigned int _dl_osversion;
 150
 151 /* All known directories in sorted order.  */
 152 struct r_search_path_elem *_dl_all_dirs;
 153
 154 /* All directories after startup.  */
 155 struct r_search_path_elem *_dl_init_all_dirs;
 156
 157 /* The object to be initialized first.  */
 158 struct link_map *_dl_initfirst;
 159
 160 /* Descriptor to write debug messages to.  */
 161 int _dl_debug_fd = STDERR_FILENO;
 162
 163 int _dl_correct_cache_id = _DL_CACHE_DEFAULT_ID;
 164
 165 ElfW(auxv_t) *_dl_auxv;
 166 const ElfW(Phdr) *_dl_phdr;
 167 size_t _dl_phnum;
 168 uint64_t _dl_hwcap __attribute__ ((nocommon));
 169 uint64_t _dl_hwcap2 __attribute__ ((nocommon));
 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 __attribute__ ((nocommon));
 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 loading a shared object requires that we make the stack executable
 189    when it was not, we do it by calling this function.
 190    It returns an errno code or zero on success.  */
 191 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 192
 193
 194 #if THREAD_GSCOPE_IN_TCB
 195 list_t _dl_stack_used;
 196 list_t _dl_stack_user;
 197 int _dl_stack_cache_lock;
 198 #else
 199 int _dl_thread_gscope_count;
 200 #endif
 201 struct dl_scope_free_list *_dl_scope_free_list;
 202
 203 #ifdef NEED_DL_SYSINFO
 204 /* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
 205    initialize it here to avoid RELATIVE relocation in static PIE.  */
 206 uintptr_t _dl_sysinfo;
 207 #endif
 208 #ifdef NEED_DL_SYSINFO_DSO
 209 /* Address of the ELF headers in the vsyscall page.  */
 210 const ElfW(Ehdr) *_dl_sysinfo_dso;
 211
 212 struct link_map *_dl_sysinfo_map;
 213
 214 # include "get-dynamic-info.h"
 215 #endif
 216 #include "setup-vdso.h"
 217 /* Define the vDSO function pointers.  */
 218 #include <dl-vdso-setup.c>
 219
 220 /* During the program run we must not modify the global data of
 221    loaded shared object simultanously in two threads.  Therefore we
 222    protect `_dl_open' and `_dl_close' in dl-close.c.
 223
 224    This must be a recursive lock since the initializer function of
 225    the loaded object might as well require a call to this function.
 226    At this time it is not anymore a problem to modify the tables.  */
 227 __rtld_lock_define_initialized_recursive (, _dl_load_lock)
 228 /* This lock is used to keep __dl_iterate_phdr from inspecting the
 229    list of loaded objects while an object is added to or removed from
 230    that list.  */
 231 __rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
 232
 233
 234 #ifdef HAVE_AUX_VECTOR
 235 int _dl_clktck;
 236
 237 void
 238 _dl_aux_init (ElfW(auxv_t) *av)
 239 {
 240   int seen = 0;
 241   uid_t uid = 0;
 242   gid_t gid = 0;
 243
 244 #ifdef NEED_DL_SYSINFO
 245   /* NB: Avoid RELATIVE relocation in static PIE.  */
 246   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 247 #endif
 248
 249   _dl_auxv = av;
 250   for (; av->a_type != AT_NULL; ++av)
 251     switch (av->a_type)
 252       {
 253       case AT_PAGESZ:
 254         if (av->a_un.a_val != 0)
 255           GLRO(dl_pagesize) = av->a_un.a_val;
 256         break;
 257       case AT_CLKTCK:
 258         GLRO(dl_clktck) = av->a_un.a_val;
 259         break;
 260       case AT_PHDR:
 261         GL(dl_phdr) = (const void *) av->a_un.a_val;
 262         break;
 263       case AT_PHNUM:
 264         GL(dl_phnum) = av->a_un.a_val;
 265         break;
 266       case AT_PLATFORM:
 267         GLRO(dl_platform) = (void *) av->a_un.a_val;
 268         break;
 269       case AT_HWCAP:
 270         GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
 271         break;
 272       case AT_HWCAP2:
 273         GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
 274         break;
 275       case AT_FPUCW:
 276         GLRO(dl_fpu_control) = av->a_un.a_val;
 277         break;
 278 #ifdef NEED_DL_SYSINFO
 279       case AT_SYSINFO:
 280         GL(dl_sysinfo) = av->a_un.a_val;
 281         break;
 282 #endif
 283 #ifdef NEED_DL_SYSINFO_DSO
 284       case AT_SYSINFO_EHDR:
 285         GL(dl_sysinfo_dso) = (void *) av->a_un.a_val;
 286         break;
 287 #endif
 288       case AT_UID:
 289         uid ^= av->a_un.a_val;
 290         seen |= 1;
 291         break;
 292       case AT_EUID:
 293         uid ^= av->a_un.a_val;
 294         seen |= 2;
 295         break;
 296       case AT_GID:
 297         gid ^= av->a_un.a_val;
 298         seen |= 4;
 299         break;
 300       case AT_EGID:
 301         gid ^= av->a_un.a_val;
 302         seen |= 8;
 303         break;
 304       case AT_SECURE:
 305         seen = -1;
 306         __libc_enable_secure = av->a_un.a_val;
 307         __libc_enable_secure_decided = 1;
 308         break;
 309       case AT_RANDOM:
 310         _dl_random = (void *) av->a_un.a_val;
 311         break;
 312       case AT_MINSIGSTKSZ:
 313         _dl_minsigstacksize = av->a_un.a_val;
 314         break;
 315       DL_PLATFORM_AUXV
 316       }
 317   if (seen == 0xf)
 318     {
 319       __libc_enable_secure = uid != 0 || gid != 0;
 320       __libc_enable_secure_decided = 1;
 321     }
 322 }
 323 #endif
 324
 325
 326 void
 327 _dl_non_dynamic_init (void)
 328 {
 329   _dl_main_map.l_origin = _dl_get_origin ();
 330   _dl_main_map.l_phdr = GL(dl_phdr);
 331   _dl_main_map.l_phnum = GL(dl_phnum);
 332
 333   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 334
 335   /* Set up the data structures for the system-supplied DSO early,
 336      so they can influence _dl_init_paths.  */
 337   setup_vdso (NULL, NULL);
 338
 339   /* With vDSO setup we can initialize the function pointers.  */
 340   setup_vdso_pointers ();
 341
 342   /* Initialize the data structures for the search paths for shared
 343      objects.  */
 344   _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
 345                   /* No glibc-hwcaps selection support in statically
 346                      linked binaries.  */
 347                   NULL, NULL);
 348
 349   /* Remember the last search directory added at startup.  */
 350   _dl_init_all_dirs = GL(dl_all_dirs);
 351
 352   _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 353
 354   _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
 355
 356   _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
 357
 358   _dl_profile_output = getenv ("LD_PROFILE_OUTPUT");
 359   if (_dl_profile_output == NULL || _dl_profile_output[0] == '\0')
 360     _dl_profile_output
 361       = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];
 362
 363   if (__libc_enable_secure)
 364     {
 365       static const char unsecure_envvars[] =
 366         UNSECURE_ENVVARS
 367 #ifdef EXTRA_UNSECURE_ENVVARS
 368         EXTRA_UNSECURE_ENVVARS
 369 #endif
 370         ;
 371       const char *cp = unsecure_envvars;
 372
 373       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 374         {
 375           __unsetenv (cp);
 376           cp = (const char *) __rawmemchr (cp, '\0') + 1;
 377         }
 378
 379 #if !HAVE_TUNABLES
 380       if (__access ("/etc/suid-debug", F_OK) != 0)
 381         __unsetenv ("MALLOC_CHECK_");
 382 #endif
 383     }
 384
 385 #ifdef DL_PLATFORM_INIT
 386   DL_PLATFORM_INIT;
 387 #endif
 388
 389 #ifdef DL_OSVERSION_INIT
 390   DL_OSVERSION_INIT;
 391 #endif
 392
 393   /* Now determine the length of the platform string.  */
 394   if (_dl_platform != NULL)
 395     _dl_platformlen = strlen (_dl_platform);
 396
 397   if (_dl_phdr != NULL)
 398     for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 399       switch (ph->p_type)
 400         {
 401         /* Check if the stack is nonexecutable.  */
 402         case PT_GNU_STACK:
 403           _dl_stack_flags = ph->p_flags;
 404           break;
 405
 406         case PT_GNU_RELRO:
 407           _dl_main_map.l_relro_addr = ph->p_vaddr;
 408           _dl_main_map.l_relro_size = ph->p_memsz;
 409           break;
 410         }
 411
 412   /* Setup relro on the binary itself.  */
 413   if (_dl_main_map.l_relro_size != 0)
 414     _dl_protect_relro (&_dl_main_map);
 415 }
 416
 417 #ifdef DL_SYSINFO_IMPLEMENTATION
 418 DL_SYSINFO_IMPLEMENTATION
 419 #endif
 420
 421 #if ENABLE_STATIC_PIE
 422 /* Since relocation to hidden _dl_main_map causes relocation overflow on
 423    aarch64, a function is used to get the address of _dl_main_map.  */
 424
 425 struct link_map *
 426 _dl_get_dl_main_map (void)
 427 {
 428   return &_dl_main_map;
 429 }
 430 #endif