elf/dl-sysdep.c

   1 /* Operating system support for run-time dynamic linker.  Generic Unix version.
   2    Copyright (C) 1995-2021 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 /* We conditionalize the whole of this file rather than simply eliding it
  20    from the static build, because other sysdeps/ versions of this file
  21    might define things needed by a static build.  */
  22
  23 #ifdef SHARED
  24
  25 #include <assert.h>
  26 #include <elf.h>
  27 #include <errno.h>
  28 #include <fcntl.h>
  29 #include <libintl.h>
  30 #include <stdlib.h>
  31 #include <string.h>
  32 #include <unistd.h>
  33 #include <sys/types.h>
  34 #include <sys/stat.h>
  35 #include <sys/mman.h>
  36 #include <ldsodefs.h>
  37 #include <_itoa.h>
  38 #include <fpu_control.h>
  39
  40 #include <entry.h>
  41 #include <dl-machine.h>
  42 #include <dl-procinfo.h>
  43 #include <dl-osinfo.h>
  44 #include <libc-internal.h>
  45 #include <tls.h>
  46
  47 #include <dl-tunables.h>
  48 #include <dl-auxv.h>
  49
  50 extern char **_environ attribute_hidden;
  51 extern char _end[] attribute_hidden;
  52
  53 /* Protect SUID program against misuse of file descriptors.  */
  54 extern void __libc_check_standard_fds (void);
  55
  56 #ifdef NEED_DL_BASE_ADDR
  57 ElfW(Addr) _dl_base_addr;
  58 #endif
  59 int __libc_enable_secure attribute_relro = 0;
  60 rtld_hidden_data_def (__libc_enable_secure)
  61 /* This variable contains the lowest stack address ever used.  */
  62 void *__libc_stack_end attribute_relro = NULL;
  63 rtld_hidden_data_def(__libc_stack_end)
  64 void *_dl_random attribute_relro = NULL;
  65
  66 #ifndef DL_FIND_ARG_COMPONENTS
  67 # define DL_FIND_ARG_COMPONENTS(cookie, argc, argv, envp, auxp) \
  68   do {                                                                        \
  69     void **_tmp;                                                              \
  70     (argc) = *(long int *) cookie;                                            \
  71     (argv) = (char **) ((long int *) cookie + 1);                             \
  72     (envp) = (argv) + (argc) + 1;                                             \
  73     for (_tmp = (void **) (envp); *_tmp; ++_tmp)                              \
  74       continue;                                                               \
  75     (auxp) = (void *) ++_tmp;                                                 \
  76   } while (0)
  77 #endif
  78
  79 #ifndef DL_STACK_END
  80 # define DL_STACK_END(cookie) ((void *) (cookie))
  81 #endif
  82
  83 ElfW(Addr)
  84 _dl_sysdep_start (void **start_argptr,
  85                   void (*dl_main) (const ElfW(Phdr) *phdr, ElfW(Word) phnum,
  86                                    ElfW(Addr) *user_entry, ElfW(auxv_t) *auxv))
  87 {
  88   const ElfW(Phdr) *phdr = NULL;
  89   ElfW(Word) phnum = 0;
  90   ElfW(Addr) user_entry;
  91   ElfW(auxv_t) *av;
  92 #ifdef HAVE_AUX_SECURE
  93 # define set_seen(tag) (tag)    /* Evaluate for the side effects.  */
  94 # define set_seen_secure() ((void) 0)
  95 #else
  96   uid_t uid = 0;
  97   gid_t gid = 0;
  98   unsigned int seen = 0;
  99 # define set_seen_secure() (seen = -1)
 100 # ifdef HAVE_AUX_XID
 101 #  define set_seen(tag) (tag)   /* Evaluate for the side effects.  */
 102 # else
 103 #  define M(type) (1 << (type))
 104 #  define set_seen(tag) seen |= M ((tag)->a_type)
 105 # endif
 106 #endif
 107 #ifdef NEED_DL_SYSINFO
 108   uintptr_t new_sysinfo = 0;
 109 #endif
 110
 111   __libc_stack_end = DL_STACK_END (start_argptr);
 112   DL_FIND_ARG_COMPONENTS (start_argptr, _dl_argc, _dl_argv, _environ,
 113                           GLRO(dl_auxv));
 114
 115   user_entry = (ElfW(Addr)) ENTRY_POINT;
 116   GLRO(dl_platform) = NULL; /* Default to nothing known about the platform.  */
 117
 118   /* NB: Default to a constant CONSTANT_MINSIGSTKSZ.  */
 119   _Static_assert (__builtin_constant_p (CONSTANT_MINSIGSTKSZ),
 120                   "CONSTANT_MINSIGSTKSZ is constant");
 121   GLRO(dl_minsigstacksize) = CONSTANT_MINSIGSTKSZ;
 122
 123   for (av = GLRO(dl_auxv); av->a_type != AT_NULL; set_seen (av++))
 124     switch (av->a_type)
 125       {
 126       case AT_PHDR:
 127         phdr = (void *) av->a_un.a_val;
 128         break;
 129       case AT_PHNUM:
 130         phnum = av->a_un.a_val;
 131         break;
 132       case AT_PAGESZ:
 133         GLRO(dl_pagesize) = av->a_un.a_val;
 134         break;
 135       case AT_ENTRY:
 136         user_entry = av->a_un.a_val;
 137         break;
 138 #ifdef NEED_DL_BASE_ADDR
 139       case AT_BASE:
 140         _dl_base_addr = av->a_un.a_val;
 141         break;
 142 #endif
 143 #ifndef HAVE_AUX_SECURE
 144       case AT_UID:
 145       case AT_EUID:
 146         uid ^= av->a_un.a_val;
 147         break;
 148       case AT_GID:
 149       case AT_EGID:
 150         gid ^= av->a_un.a_val;
 151         break;
 152 #endif
 153       case AT_SECURE:
 154 #ifndef HAVE_AUX_SECURE
 155         seen = -1;
 156 #endif
 157         __libc_enable_secure = av->a_un.a_val;
 158         break;
 159       case AT_PLATFORM:
 160         GLRO(dl_platform) = (void *) av->a_un.a_val;
 161         break;
 162       case AT_HWCAP:
 163         GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
 164         break;
 165       case AT_HWCAP2:
 166         GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
 167         break;
 168       case AT_CLKTCK:
 169         GLRO(dl_clktck) = av->a_un.a_val;
 170         break;
 171       case AT_FPUCW:
 172         GLRO(dl_fpu_control) = av->a_un.a_val;
 173         break;
 174 #ifdef NEED_DL_SYSINFO
 175       case AT_SYSINFO:
 176         new_sysinfo = av->a_un.a_val;
 177         break;
 178 #endif
 179 #ifdef NEED_DL_SYSINFO_DSO
 180       case AT_SYSINFO_EHDR:
 181         GLRO(dl_sysinfo_dso) = (void *) av->a_un.a_val;
 182         break;
 183 #endif
 184       case AT_RANDOM:
 185         _dl_random = (void *) av->a_un.a_val;
 186         break;
 187       case AT_MINSIGSTKSZ:
 188         GLRO(dl_minsigstacksize) = av->a_un.a_val;
 189         break;
 190       DL_PLATFORM_AUXV
 191       }
 192
 193 #ifndef HAVE_AUX_SECURE
 194   if (seen != -1)
 195     {
 196       /* Fill in the values we have not gotten from the kernel through the
 197          auxiliary vector.  */
 198 # ifndef HAVE_AUX_XID
 199 #  define SEE(UID, var, uid) \
 200    if ((seen & M (AT_##UID)) == 0) var ^= __get##uid ()
 201       SEE (UID, uid, uid);
 202       SEE (EUID, uid, euid);
 203       SEE (GID, gid, gid);
 204       SEE (EGID, gid, egid);
 205 # endif
 206
 207       /* If one of the two pairs of IDs does not match this is a setuid
 208          or setgid run.  */
 209       __libc_enable_secure = uid | gid;
 210     }
 211 #endif
 212
 213 #ifndef HAVE_AUX_PAGESIZE
 214   if (GLRO(dl_pagesize) == 0)
 215     GLRO(dl_pagesize) = __getpagesize ();
 216 #endif
 217
 218 #ifdef NEED_DL_SYSINFO
 219   if (new_sysinfo != 0)
 220     {
 221 # ifdef NEED_DL_SYSINFO_DSO
 222       /* Only set the sysinfo value if we also have the vsyscall DSO.  */
 223       if (GLRO(dl_sysinfo_dso) != 0)
 224 # endif
 225         GLRO(dl_sysinfo) = new_sysinfo;
 226     }
 227 #endif
 228
 229   __tunables_init (_environ);
 230
 231 #ifdef DL_SYSDEP_INIT
 232   DL_SYSDEP_INIT;
 233 #endif
 234
 235 #ifdef DL_PLATFORM_INIT
 236   DL_PLATFORM_INIT;
 237 #endif
 238
 239   /* Determine the length of the platform name.  */
 240   if (GLRO(dl_platform) != NULL)
 241     GLRO(dl_platformlen) = strlen (GLRO(dl_platform));
 242
 243   if (__sbrk (0) == _end)
 244     /* The dynamic linker was run as a program, and so the initial break
 245        starts just after our bss, at &_end.  The malloc in dl-minimal.c
 246        will consume the rest of this page, so tell the kernel to move the
 247        break up that far.  When the user program examines its break, it
 248        will see this new value and not clobber our data.  */
 249     __sbrk (GLRO(dl_pagesize)
 250             - ((_end - (char *) 0) & (GLRO(dl_pagesize) - 1)));
 251
 252   /* If this is a SUID program we make sure that FDs 0, 1, and 2 are
 253      allocated.  If necessary we are doing it ourself.  If it is not
 254      possible we stop the program.  */
 255   if (__builtin_expect (__libc_enable_secure, 0))
 256     __libc_check_standard_fds ();
 257
 258   (*dl_main) (phdr, phnum, &user_entry, GLRO(dl_auxv));
 259   return user_entry;
 260 }
 261
 262 void
 263 _dl_sysdep_start_cleanup (void)
 264 {
 265 }
 266
 267 void
 268 _dl_show_auxv (void)
 269 {
 270   char buf[64];
 271   ElfW(auxv_t) *av;
 272
 273   /* Terminate string.  */
 274   buf[63] = '\0';
 275
 276   /* The following code assumes that the AT_* values are encoded
 277      starting from 0 with AT_NULL, 1 for AT_IGNORE, and all other values
 278      close by (otherwise the array will be too large).  In case we have
 279      to support a platform where these requirements are not fulfilled
 280      some alternative implementation has to be used.  */
 281   for (av = GLRO(dl_auxv); av->a_type != AT_NULL; ++av)
 282     {
 283       static const struct
 284       {
 285         const char label[22];
 286         enum { unknown = 0, dec, hex, str, ignore } form : 8;
 287       } auxvars[] =
 288         {
 289           [AT_EXECFD - 2] =             { "EXECFD:            ", dec },
 290           [AT_EXECFN - 2] =             { "EXECFN:            ", str },
 291           [AT_PHDR - 2] =               { "PHDR:              0x", hex },
 292           [AT_PHENT - 2] =              { "PHENT:             ", dec },
 293           [AT_PHNUM - 2] =              { "PHNUM:             ", dec },
 294           [AT_PAGESZ - 2] =             { "PAGESZ:            ", dec },
 295           [AT_BASE - 2] =               { "BASE:              0x", hex },
 296           [AT_FLAGS - 2] =              { "FLAGS:             0x", hex },
 297           [AT_ENTRY - 2] =              { "ENTRY:             0x", hex },
 298           [AT_NOTELF - 2] =             { "NOTELF:            ", hex },
 299           [AT_UID - 2] =                { "UID:               ", dec },
 300           [AT_EUID - 2] =               { "EUID:              ", dec },
 301           [AT_GID - 2] =                { "GID:               ", dec },
 302           [AT_EGID - 2] =               { "EGID:              ", dec },
 303           [AT_PLATFORM - 2] =           { "PLATFORM:          ", str },
 304           [AT_HWCAP - 2] =              { "HWCAP:             ", hex },
 305           [AT_CLKTCK - 2] =             { "CLKTCK:            ", dec },
 306           [AT_FPUCW - 2] =              { "FPUCW:             ", hex },
 307           [AT_DCACHEBSIZE - 2] =        { "DCACHEBSIZE:       0x", hex },
 308           [AT_ICACHEBSIZE - 2] =        { "ICACHEBSIZE:       0x", hex },
 309           [AT_UCACHEBSIZE - 2] =        { "UCACHEBSIZE:       0x", hex },
 310           [AT_IGNOREPPC - 2] =          { "IGNOREPPC", ignore },
 311           [AT_SECURE - 2] =             { "SECURE:            ", dec },
 312           [AT_BASE_PLATFORM - 2] =      { "BASE_PLATFORM:     ", str },
 313           [AT_SYSINFO - 2] =            { "SYSINFO:           0x", hex },
 314           [AT_SYSINFO_EHDR - 2] =       { "SYSINFO_EHDR:      0x", hex },
 315           [AT_RANDOM - 2] =             { "RANDOM:            0x", hex },
 316           [AT_HWCAP2 - 2] =             { "HWCAP2:            0x", hex },
 317           [AT_MINSIGSTKSZ - 2] =        { "MINSIGSTKSZ        ", dec },
 318           [AT_L1I_CACHESIZE - 2] =      { "L1I_CACHESIZE:     ", dec },
 319           [AT_L1I_CACHEGEOMETRY - 2] =  { "L1I_CACHEGEOMETRY: 0x", hex },
 320           [AT_L1D_CACHESIZE - 2] =      { "L1D_CACHESIZE:     ", dec },
 321           [AT_L1D_CACHEGEOMETRY - 2] =  { "L1D_CACHEGEOMETRY: 0x", hex },
 322           [AT_L2_CACHESIZE - 2] =       { "L2_CACHESIZE:      ", dec },
 323           [AT_L2_CACHEGEOMETRY - 2] =   { "L2_CACHEGEOMETRY:  0x", hex },
 324           [AT_L3_CACHESIZE - 2] =       { "L3_CACHESIZE:      ", dec },
 325           [AT_L3_CACHEGEOMETRY - 2] =   { "L3_CACHEGEOMETRY:  0x", hex },
 326         };
 327       unsigned int idx = (unsigned int) (av->a_type - 2);
 328
 329       if ((unsigned int) av->a_type < 2u
 330           || (idx < sizeof (auxvars) / sizeof (auxvars[0])
 331               && auxvars[idx].form == ignore))
 332         continue;
 333
 334       assert (AT_NULL == 0);
 335       assert (AT_IGNORE == 1);
 336
 337       /* Some entries are handled in a special way per platform.  */
 338       if (_dl_procinfo (av->a_type, av->a_un.a_val) == 0)
 339         continue;
 340
 341       if (idx < sizeof (auxvars) / sizeof (auxvars[0])
 342           && auxvars[idx].form != unknown)
 343         {
 344           const char *val = (char *) av->a_un.a_val;
 345
 346           if (__builtin_expect (auxvars[idx].form, dec) == dec)
 347             val = _itoa ((unsigned long int) av->a_un.a_val,
 348                          buf + sizeof buf - 1, 10, 0);
 349           else if (__builtin_expect (auxvars[idx].form, hex) == hex)
 350             val = _itoa ((unsigned long int) av->a_un.a_val,
 351                          buf + sizeof buf - 1, 16, 0);
 352
 353           _dl_printf ("AT_%s%s\n", auxvars[idx].label, val);
 354
 355           continue;
 356         }
 357
 358       /* Unknown value: print a generic line.  */
 359       char buf2[17];
 360       buf2[sizeof (buf2) - 1] = '\0';
 361       const char *val2 = _itoa ((unsigned long int) av->a_un.a_val,
 362                                 buf2 + sizeof buf2 - 1, 16, 0);
 363       const char *val =  _itoa ((unsigned long int) av->a_type,
 364                                 buf + sizeof buf - 1, 16, 0);
 365       _dl_printf ("AT_??? (0x%s): 0x%s\n", val, val2);
 366     }
 367 }
 368
 369 #endif