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 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 __attribute__ ((nocommon));
 167 uint64_t _dl_hwcap2 __attribute__ ((nocommon));
 168
 169 /* The value of the FPU control word the kernel will preset in hardware.  */
 170 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 171
 172 #if !HAVE_TUNABLES
 173 /* This is not initialized to HWCAP_IMPORTANT, matching the definition
 174    of _dl_important_hwcaps, below, where no hwcap strings are ever
 175    used.  This mask is still used to mediate the lookups in the cache
 176    file.  Since there is no way to set this nonzero (we don't grok the
 177    LD_HWCAP_MASK environment variable here), there is no real point in
 178    setting _dl_hwcap nonzero below, but we do anyway.  */
 179 uint64_t _dl_hwcap_mask __attribute__ ((nocommon));
 180 #endif
 181
 182 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 183  * executable but this isn't true for all platforms.  */
 184 ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;
 185
 186 /* If loading a shared object requires that we make the stack executable
 187    when it was not, we do it by calling this function.
 188    It returns an errno code or zero on success.  */
 189 int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
 190
 191
 192 #if THREAD_GSCOPE_IN_TCB
 193 list_t _dl_stack_used;
 194 list_t _dl_stack_user;
 195 int _dl_stack_cache_lock;
 196 #else
 197 int _dl_thread_gscope_count;
 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
 231
 232 #ifdef HAVE_AUX_VECTOR
 233 int _dl_clktck;
 234
 235 void
 236 _dl_aux_init (ElfW(auxv_t) *av)
 237 {
 238   int seen = 0;
 239   uid_t uid = 0;
 240   gid_t gid = 0;
 241
 242 #ifdef NEED_DL_SYSINFO
 243   /* NB: Avoid RELATIVE relocation in static PIE.  */
 244   GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
 245 #endif
 246
 247   _dl_auxv = av;
 248   for (; av->a_type != AT_NULL; ++av)
 249     switch (av->a_type)
 250       {
 251       case AT_PAGESZ:
 252         if (av->a_un.a_val != 0)
 253           GLRO(dl_pagesize) = av->a_un.a_val;
 254         break;
 255       case AT_CLKTCK:
 256         GLRO(dl_clktck) = av->a_un.a_val;
 257         break;
 258       case AT_PHDR:
 259         GL(dl_phdr) = (const void *) av->a_un.a_val;
 260         break;
 261       case AT_PHNUM:
 262         GL(dl_phnum) = av->a_un.a_val;
 263         break;
 264       case AT_PLATFORM:
 265         GLRO(dl_platform) = (void *) av->a_un.a_val;
 266         break;
 267       case AT_HWCAP:
 268         GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
 269         break;
 270       case AT_HWCAP2:
 271         GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
 272         break;
 273       case AT_FPUCW:
 274         GLRO(dl_fpu_control) = av->a_un.a_val;
 275         break;
 276 #ifdef NEED_DL_SYSINFO
 277       case AT_SYSINFO:
 278         GL(dl_sysinfo) = av->a_un.a_val;
 279         break;
 280 #endif
 281 #ifdef NEED_DL_SYSINFO_DSO
 282       case AT_SYSINFO_EHDR:
 283         GL(dl_sysinfo_dso) = (void *) av->a_un.a_val;
 284         break;
 285 #endif
 286       case AT_UID:
 287         uid ^= av->a_un.a_val;
 288         seen |= 1;
 289         break;
 290       case AT_EUID:
 291         uid ^= av->a_un.a_val;
 292         seen |= 2;
 293         break;
 294       case AT_GID:
 295         gid ^= av->a_un.a_val;
 296         seen |= 4;
 297         break;
 298       case AT_EGID:
 299         gid ^= av->a_un.a_val;
 300         seen |= 8;
 301         break;
 302       case AT_SECURE:
 303         seen = -1;
 304         __libc_enable_secure = av->a_un.a_val;
 305         __libc_enable_secure_decided = 1;
 306         break;
 307       case AT_RANDOM:
 308         _dl_random = (void *) av->a_un.a_val;
 309         break;
 310       DL_PLATFORM_AUXV
 311       }
 312   if (seen == 0xf)
 313     {
 314       __libc_enable_secure = uid != 0 || gid != 0;
 315       __libc_enable_secure_decided = 1;
 316     }
 317 }
 318 #endif
 319
 320
 321 void
 322 _dl_non_dynamic_init (void)
 323 {
 324   _dl_main_map.l_origin = _dl_get_origin ();
 325   _dl_main_map.l_phdr = GL(dl_phdr);
 326   _dl_main_map.l_phnum = GL(dl_phnum);
 327
 328   _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;
 329
 330   /* Set up the data structures for the system-supplied DSO early,
 331      so they can influence _dl_init_paths.  */
 332   setup_vdso (NULL, NULL);
 333
 334   /* With vDSO setup we can initialize the function pointers.  */
 335   setup_vdso_pointers ();
 336
 337   /* Initialize the data structures for the search paths for shared
 338      objects.  */
 339   _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
 340                   /* No glibc-hwcaps selection support in statically
 341                      linked binaries.  */
 342                   NULL, NULL);
 343
 344   /* Remember the last search directory added at startup.  */
 345   _dl_init_all_dirs = GL(dl_all_dirs);
 346
 347   _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';
 348
 349   _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';
 350
 351   _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';
 352
 353   _dl_profile_output = getenv ("LD_PROFILE_OUTPUT");
 354   if (_dl_profile_output == NULL || _dl_profile_output[0] == '\0')
 355     _dl_profile_output
 356       = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];
 357
 358   if (__libc_enable_secure)
 359     {
 360       static const char unsecure_envvars[] =
 361         UNSECURE_ENVVARS
 362 #ifdef EXTRA_UNSECURE_ENVVARS
 363         EXTRA_UNSECURE_ENVVARS
 364 #endif
 365         ;
 366       const char *cp = unsecure_envvars;
 367
 368       while (cp < unsecure_envvars + sizeof (unsecure_envvars))
 369         {
 370           __unsetenv (cp);
 371           cp = (const char *) __rawmemchr (cp, '\0') + 1;
 372         }
 373
 374 #if !HAVE_TUNABLES
 375       if (__access ("/etc/suid-debug", F_OK) != 0)
 376         __unsetenv ("MALLOC_CHECK_");
 377 #endif
 378     }
 379
 380 #ifdef DL_PLATFORM_INIT
 381   DL_PLATFORM_INIT;
 382 #endif
 383
 384 #ifdef DL_OSVERSION_INIT
 385   DL_OSVERSION_INIT;
 386 #endif
 387
 388   /* Now determine the length of the platform string.  */
 389   if (_dl_platform != NULL)
 390     _dl_platformlen = strlen (_dl_platform);
 391
 392   if (_dl_phdr != NULL)
 393     for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
 394       switch (ph->p_type)
 395         {
 396         /* Check if the stack is nonexecutable.  */
 397         case PT_GNU_STACK:
 398           _dl_stack_flags = ph->p_flags;
 399           break;
 400
 401         case PT_GNU_RELRO:
 402           _dl_main_map.l_relro_addr = ph->p_vaddr;
 403           _dl_main_map.l_relro_size = ph->p_memsz;
 404           break;
 405         }
 406
 407   /* Setup relro on the binary itself.  */
 408   if (_dl_main_map.l_relro_size != 0)
 409     _dl_protect_relro (&_dl_main_map);
 410 }
 411
 412 #ifdef DL_SYSINFO_IMPLEMENTATION
 413 DL_SYSINFO_IMPLEMENTATION
 414 #endif
 415
 416 #if ENABLE_STATIC_PIE
 417 /* Since relocation to hidden _dl_main_map causes relocation overflow on
 418    aarch64, a function is used to get the address of _dl_main_map.  */
 419
 420 struct link_map *
 421 _dl_get_dl_main_map (void)
 422 {
 423   return &_dl_main_map;
 424 }
 425 #endif