elf/dl-sysdep.c

   1 /* Operating system support for run-time dynamic linker.  Generic Unix version.
   2    Copyright (C) 1995-2017 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    <http://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
  49 extern char **_environ attribute_hidden;
  50 extern char _end[] attribute_hidden;
  51
  52 /* Protect SUID program against misuse of file descriptors.  */
  53 extern void __libc_check_standard_fds (void);
  54
  55 #ifdef NEED_DL_BASE_ADDR
  56 ElfW(Addr) _dl_base_addr;
  57 #endif
  58 int __libc_enable_secure attribute_relro = 0;
  59 rtld_hidden_data_def (__libc_enable_secure)
  60 int __libc_multiple_libcs = 0;  /* Defining this here avoids the inclusion
  61                                    of init-first.  */
  62 /* This variable contains the lowest stack address ever used.  */
  63 void *__libc_stack_end attribute_relro = NULL;
  64 rtld_hidden_data_def(__libc_stack_end)
  65 void *_dl_random attribute_relro = NULL;
  66
  67 #ifndef DL_FIND_ARG_COMPONENTS
  68 # define DL_FIND_ARG_COMPONENTS(cookie, argc, argv, envp, auxp) \
  69   do {                                                                        \
  70     void **_tmp;                                                              \
  71     (argc) = *(long int *) cookie;                                            \
  72     (argv) = (char **) ((long int *) cookie + 1);                             \
  73     (envp) = (argv) + (argc) + 1;                                             \
  74     for (_tmp = (void **) (envp); *_tmp; ++_tmp)                              \
  75       continue;                                                               \
  76     (auxp) = (void *) ++_tmp;                                                 \
  77   } while (0)
  78 #endif
  79
  80 #ifndef DL_STACK_END
  81 # define DL_STACK_END(cookie) ((void *) (cookie))
  82 #endif
  83
  84 ElfW(Addr)
  85 _dl_sysdep_start (void **start_argptr,
  86                   void (*dl_main) (const ElfW(Phdr) *phdr, ElfW(Word) phnum,
  87                                    ElfW(Addr) *user_entry, ElfW(auxv_t) *auxv))
  88 {
  89   const ElfW(Phdr) *phdr = NULL;
  90   ElfW(Word) phnum = 0;
  91   ElfW(Addr) user_entry;
  92   ElfW(auxv_t) *av;
  93 #ifdef HAVE_AUX_SECURE
  94 # define set_seen(tag) (tag)    /* Evaluate for the side effects.  */
  95 # define set_seen_secure() ((void) 0)
  96 #else
  97   uid_t uid = 0;
  98   gid_t gid = 0;
  99   unsigned int seen = 0;
 100 # define set_seen_secure() (seen = -1)
 101 # ifdef HAVE_AUX_XID
 102 #  define set_seen(tag) (tag)   /* Evaluate for the side effects.  */
 103 # else
 104 #  define M(type) (1 << (type))
 105 #  define set_seen(tag) seen |= M ((tag)->a_type)
 106 # endif
 107 #endif
 108 #ifdef NEED_DL_SYSINFO
 109   uintptr_t new_sysinfo = 0;
 110 #endif
 111
 112   __libc_stack_end = DL_STACK_END (start_argptr);
 113   DL_FIND_ARG_COMPONENTS (start_argptr, _dl_argc, _dl_argv, _environ,
 114                           GLRO(dl_auxv));
 115
 116   user_entry = (ElfW(Addr)) ENTRY_POINT;
 117   GLRO(dl_platform) = NULL; /* Default to nothing known about the platform.  */
 118
 119   for (av = GLRO(dl_auxv); av->a_type != AT_NULL; set_seen (av++))
 120     switch (av->a_type)
 121       {
 122       case AT_PHDR:
 123         phdr = (void *) av->a_un.a_val;
 124         break;
 125       case AT_PHNUM:
 126         phnum = av->a_un.a_val;
 127         break;
 128       case AT_PAGESZ:
 129         GLRO(dl_pagesize) = av->a_un.a_val;
 130         break;
 131       case AT_ENTRY:
 132         user_entry = av->a_un.a_val;
 133         break;
 134 #ifdef NEED_DL_BASE_ADDR
 135       case AT_BASE:
 136         _dl_base_addr = av->a_un.a_val;
 137         break;
 138 #endif
 139 #ifndef HAVE_AUX_SECURE
 140       case AT_UID:
 141       case AT_EUID:
 142         uid ^= av->a_un.a_val;
 143         break;
 144       case AT_GID:
 145       case AT_EGID:
 146         gid ^= av->a_un.a_val;
 147         break;
 148 #endif
 149       case AT_SECURE:
 150 #ifndef HAVE_AUX_SECURE
 151         seen = -1;
 152 #endif
 153         __libc_enable_secure = av->a_un.a_val;
 154         break;
 155       case AT_PLATFORM:
 156         GLRO(dl_platform) = (void *) av->a_un.a_val;
 157         break;
 158       case AT_HWCAP:
 159         GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
 160         break;
 161       case AT_HWCAP2:
 162         GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
 163         break;
 164       case AT_CLKTCK:
 165         GLRO(dl_clktck) = av->a_un.a_val;
 166         break;
 167       case AT_FPUCW:
 168         GLRO(dl_fpu_control) = av->a_un.a_val;
 169         break;
 170 #ifdef NEED_DL_SYSINFO
 171       case AT_SYSINFO:
 172         new_sysinfo = av->a_un.a_val;
 173         break;
 174 #endif
 175 #ifdef NEED_DL_SYSINFO_DSO
 176       case AT_SYSINFO_EHDR:
 177         GLRO(dl_sysinfo_dso) = (void *) av->a_un.a_val;
 178         break;
 179 #endif
 180       case AT_RANDOM:
 181         _dl_random = (void *) av->a_un.a_val;
 182         break;
 183 #ifdef DL_PLATFORM_AUXV
 184       DL_PLATFORM_AUXV
 185 #endif
 186       }
 187
 188 #ifndef HAVE_AUX_SECURE
 189   if (seen != -1)
 190     {
 191       /* Fill in the values we have not gotten from the kernel through the
 192          auxiliary vector.  */
 193 # ifndef HAVE_AUX_XID
 194 #  define SEE(UID, var, uid) \
 195    if ((seen & M (AT_##UID)) == 0) var ^= __get##uid ()
 196       SEE (UID, uid, uid);
 197       SEE (EUID, uid, euid);
 198       SEE (GID, gid, gid);
 199       SEE (EGID, gid, egid);
 200 # endif
 201
 202       /* If one of the two pairs of IDs does not match this is a setuid
 203          or setgid run.  */
 204       __libc_enable_secure = uid | gid;
 205     }
 206 #endif
 207
 208 #ifndef HAVE_AUX_PAGESIZE
 209   if (GLRO(dl_pagesize) == 0)
 210     GLRO(dl_pagesize) = __getpagesize ();
 211 #endif
 212
 213 #ifdef NEED_DL_SYSINFO
 214   if (new_sysinfo != 0)
 215     {
 216 # ifdef NEED_DL_SYSINFO_DSO
 217       /* Only set the sysinfo value if we also have the vsyscall DSO.  */
 218       if (GLRO(dl_sysinfo_dso) != 0)
 219 # endif
 220         GLRO(dl_sysinfo) = new_sysinfo;
 221     }
 222 #endif
 223
 224   __tunables_init (_environ);
 225
 226 #ifdef DL_SYSDEP_INIT
 227   DL_SYSDEP_INIT;
 228 #endif
 229
 230 #ifdef DL_PLATFORM_INIT
 231   DL_PLATFORM_INIT;
 232 #endif
 233
 234   /* Determine the length of the platform name.  */
 235   if (GLRO(dl_platform) != NULL)
 236     GLRO(dl_platformlen) = strlen (GLRO(dl_platform));
 237
 238   if (__sbrk (0) == _end)
 239     /* The dynamic linker was run as a program, and so the initial break
 240        starts just after our bss, at &_end.  The malloc in dl-minimal.c
 241        will consume the rest of this page, so tell the kernel to move the
 242        break up that far.  When the user program examines its break, it
 243        will see this new value and not clobber our data.  */
 244     __sbrk (GLRO(dl_pagesize)
 245             - ((_end - (char *) 0) & (GLRO(dl_pagesize) - 1)));
 246
 247   /* If this is a SUID program we make sure that FDs 0, 1, and 2 are
 248      allocated.  If necessary we are doing it ourself.  If it is not
 249      possible we stop the program.  */
 250   if (__builtin_expect (__libc_enable_secure, 0))
 251     __libc_check_standard_fds ();
 252
 253   (*dl_main) (phdr, phnum, &user_entry, GLRO(dl_auxv));
 254   return user_entry;
 255 }
 256
 257 void
 258 _dl_sysdep_start_cleanup (void)
 259 {
 260 }
 261
 262 void
 263 _dl_show_auxv (void)
 264 {
 265   char buf[64];
 266   ElfW(auxv_t) *av;
 267
 268   /* Terminate string.  */
 269   buf[63] = '\0';
 270
 271   /* The following code assumes that the AT_* values are encoded
 272      starting from 0 with AT_NULL, 1 for AT_IGNORE, and all other values
 273      close by (otherwise the array will be too large).  In case we have
 274      to support a platform where these requirements are not fulfilled
 275      some alternative implementation has to be used.  */
 276   for (av = GLRO(dl_auxv); av->a_type != AT_NULL; ++av)
 277     {
 278       static const struct
 279       {
 280         const char label[17];
 281         enum { unknown = 0, dec, hex, str, ignore } form : 8;
 282       } auxvars[] =
 283         {
 284           [AT_EXECFD - 2] =             { "EXECFD:       ", dec },
 285           [AT_EXECFN - 2] =             { "EXECFN:       ", str },
 286           [AT_PHDR - 2] =               { "PHDR:         0x", hex },
 287           [AT_PHENT - 2] =              { "PHENT:        ", dec },
 288           [AT_PHNUM - 2] =              { "PHNUM:        ", dec },
 289           [AT_PAGESZ - 2] =             { "PAGESZ:       ", dec },
 290           [AT_BASE - 2] =               { "BASE:         0x", hex },
 291           [AT_FLAGS - 2] =              { "FLAGS:        0x", hex },
 292           [AT_ENTRY - 2] =              { "ENTRY:        0x", hex },
 293           [AT_NOTELF - 2] =             { "NOTELF:       ", hex },
 294           [AT_UID - 2] =                { "UID:          ", dec },
 295           [AT_EUID - 2] =               { "EUID:         ", dec },
 296           [AT_GID - 2] =                { "GID:          ", dec },
 297           [AT_EGID - 2] =               { "EGID:         ", dec },
 298           [AT_PLATFORM - 2] =           { "PLATFORM:     ", str },
 299           [AT_HWCAP - 2] =              { "HWCAP:        ", hex },
 300           [AT_CLKTCK - 2] =             { "CLKTCK:       ", dec },
 301           [AT_FPUCW - 2] =              { "FPUCW:        ", hex },
 302           [AT_DCACHEBSIZE - 2] =        { "DCACHEBSIZE:  0x", hex },
 303           [AT_ICACHEBSIZE - 2] =        { "ICACHEBSIZE:  0x", hex },
 304           [AT_UCACHEBSIZE - 2] =        { "UCACHEBSIZE:  0x", hex },
 305           [AT_IGNOREPPC - 2] =          { "IGNOREPPC", ignore },
 306           [AT_SECURE - 2] =             { "SECURE:       ", dec },
 307           [AT_BASE_PLATFORM - 2] =      { "BASE_PLATFORM:", str },
 308           [AT_SYSINFO - 2] =            { "SYSINFO:      0x", hex },
 309           [AT_SYSINFO_EHDR - 2] =       { "SYSINFO_EHDR: 0x", hex },
 310           [AT_RANDOM - 2] =             { "RANDOM:       0x", hex },
 311           [AT_HWCAP2 - 2] =             { "HWCAP2:       0x", hex },
 312         };
 313       unsigned int idx = (unsigned int) (av->a_type - 2);
 314
 315       if ((unsigned int) av->a_type < 2u
 316           || (idx < sizeof (auxvars) / sizeof (auxvars[0])
 317               && auxvars[idx].form == ignore))
 318         continue;
 319
 320       assert (AT_NULL == 0);
 321       assert (AT_IGNORE == 1);
 322
 323       if (av->a_type == AT_HWCAP || av->a_type == AT_HWCAP2)
 324         {
 325           /* These are handled in a special way per platform.  */
 326           if (_dl_procinfo (av->a_type, av->a_un.a_val) == 0)
 327             continue;
 328         }
 329
 330       if (idx < sizeof (auxvars) / sizeof (auxvars[0])
 331           && auxvars[idx].form != unknown)
 332         {
 333           const char *val = (char *) av->a_un.a_val;
 334
 335           if (__builtin_expect (auxvars[idx].form, dec) == dec)
 336             val = _itoa ((unsigned long int) av->a_un.a_val,
 337                          buf + sizeof buf - 1, 10, 0);
 338           else if (__builtin_expect (auxvars[idx].form, hex) == hex)
 339             val = _itoa ((unsigned long int) av->a_un.a_val,
 340                          buf + sizeof buf - 1, 16, 0);
 341
 342           _dl_printf ("AT_%s%s\n", auxvars[idx].label, val);
 343
 344           continue;
 345         }
 346
 347       /* Unknown value: print a generic line.  */
 348       char buf2[17];
 349       buf2[sizeof (buf2) - 1] = '\0';
 350       const char *val2 = _itoa ((unsigned long int) av->a_un.a_val,
 351                                 buf2 + sizeof buf2 - 1, 16, 0);
 352       const char *val =  _itoa ((unsigned long int) av->a_type,
 353                                 buf + sizeof buf - 1, 16, 0);
 354       _dl_printf ("AT_??? (0x%s): 0x%s\n", val, val2);
 355     }
 356 }
 357
 358 #endif