elf/dl-sysdep.c

   1 /* Operating system support for run-time dynamic linker.  Generic Unix version.
   2    Copyright (C) 1995-2020 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   for (av = GLRO(dl_auxv); av->a_type != AT_NULL; set_seen (av++))
 119     switch (av->a_type)
 120       {
 121       case AT_PHDR:
 122         phdr = (void *) av->a_un.a_val;
 123         break;
 124       case AT_PHNUM:
 125         phnum = av->a_un.a_val;
 126         break;
 127       case AT_PAGESZ:
 128         GLRO(dl_pagesize) = av->a_un.a_val;
 129         break;
 130       case AT_ENTRY:
 131         user_entry = av->a_un.a_val;
 132         break;
 133 #ifdef NEED_DL_BASE_ADDR
 134       case AT_BASE:
 135         _dl_base_addr = av->a_un.a_val;
 136         break;
 137 #endif
 138 #ifndef HAVE_AUX_SECURE
 139       case AT_UID:
 140       case AT_EUID:
 141         uid ^= av->a_un.a_val;
 142         break;
 143       case AT_GID:
 144       case AT_EGID:
 145         gid ^= av->a_un.a_val;
 146         break;
 147 #endif
 148       case AT_SECURE:
 149 #ifndef HAVE_AUX_SECURE
 150         seen = -1;
 151 #endif
 152         __libc_enable_secure = av->a_un.a_val;
 153         break;
 154       case AT_PLATFORM:
 155         GLRO(dl_platform) = (void *) av->a_un.a_val;
 156         break;
 157       case AT_HWCAP:
 158         GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
 159         break;
 160       case AT_HWCAP2:
 161         GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
 162         break;
 163       case AT_CLKTCK:
 164         GLRO(dl_clktck) = av->a_un.a_val;
 165         break;
 166       case AT_FPUCW:
 167         GLRO(dl_fpu_control) = av->a_un.a_val;
 168         break;
 169 #ifdef NEED_DL_SYSINFO
 170       case AT_SYSINFO:
 171         new_sysinfo = av->a_un.a_val;
 172         break;
 173 #endif
 174 #ifdef NEED_DL_SYSINFO_DSO
 175       case AT_SYSINFO_EHDR:
 176         GLRO(dl_sysinfo_dso) = (void *) av->a_un.a_val;
 177         break;
 178 #endif
 179       case AT_RANDOM:
 180         _dl_random = (void *) av->a_un.a_val;
 181         break;
 182       DL_PLATFORM_AUXV
 183       }
 184
 185 #ifndef HAVE_AUX_SECURE
 186   if (seen != -1)
 187     {
 188       /* Fill in the values we have not gotten from the kernel through the
 189          auxiliary vector.  */
 190 # ifndef HAVE_AUX_XID
 191 #  define SEE(UID, var, uid) \
 192    if ((seen & M (AT_##UID)) == 0) var ^= __get##uid ()
 193       SEE (UID, uid, uid);
 194       SEE (EUID, uid, euid);
 195       SEE (GID, gid, gid);
 196       SEE (EGID, gid, egid);
 197 # endif
 198
 199       /* If one of the two pairs of IDs does not match this is a setuid
 200          or setgid run.  */
 201       __libc_enable_secure = uid | gid;
 202     }
 203 #endif
 204
 205 #ifndef HAVE_AUX_PAGESIZE
 206   if (GLRO(dl_pagesize) == 0)
 207     GLRO(dl_pagesize) = __getpagesize ();
 208 #endif
 209
 210 #ifdef NEED_DL_SYSINFO
 211   if (new_sysinfo != 0)
 212     {
 213 # ifdef NEED_DL_SYSINFO_DSO
 214       /* Only set the sysinfo value if we also have the vsyscall DSO.  */
 215       if (GLRO(dl_sysinfo_dso) != 0)
 216 # endif
 217         GLRO(dl_sysinfo) = new_sysinfo;
 218     }
 219 #endif
 220
 221   __tunables_init (_environ);
 222
 223 #ifdef DL_SYSDEP_INIT
 224   DL_SYSDEP_INIT;
 225 #endif
 226
 227 #ifdef DL_PLATFORM_INIT
 228   DL_PLATFORM_INIT;
 229 #endif
 230
 231   /* Determine the length of the platform name.  */
 232   if (GLRO(dl_platform) != NULL)
 233     GLRO(dl_platformlen) = strlen (GLRO(dl_platform));
 234
 235   if (__sbrk (0) == _end)
 236     /* The dynamic linker was run as a program, and so the initial break
 237        starts just after our bss, at &_end.  The malloc in dl-minimal.c
 238        will consume the rest of this page, so tell the kernel to move the
 239        break up that far.  When the user program examines its break, it
 240        will see this new value and not clobber our data.  */
 241     __sbrk (GLRO(dl_pagesize)
 242             - ((_end - (char *) 0) & (GLRO(dl_pagesize) - 1)));
 243
 244   /* If this is a SUID program we make sure that FDs 0, 1, and 2 are
 245      allocated.  If necessary we are doing it ourself.  If it is not
 246      possible we stop the program.  */
 247   if (__builtin_expect (__libc_enable_secure, 0))
 248     __libc_check_standard_fds ();
 249
 250   (*dl_main) (phdr, phnum, &user_entry, GLRO(dl_auxv));
 251   return user_entry;
 252 }
 253
 254 void
 255 _dl_sysdep_start_cleanup (void)
 256 {
 257 }
 258
 259 void
 260 _dl_show_auxv (void)
 261 {
 262   char buf[64];
 263   ElfW(auxv_t) *av;
 264
 265   /* Terminate string.  */
 266   buf[63] = '\0';
 267
 268   /* The following code assumes that the AT_* values are encoded
 269      starting from 0 with AT_NULL, 1 for AT_IGNORE, and all other values
 270      close by (otherwise the array will be too large).  In case we have
 271      to support a platform where these requirements are not fulfilled
 272      some alternative implementation has to be used.  */
 273   for (av = GLRO(dl_auxv); av->a_type != AT_NULL; ++av)
 274     {
 275       static const struct
 276       {
 277         const char label[22];
 278         enum { unknown = 0, dec, hex, str, ignore } form : 8;
 279       } auxvars[] =
 280         {
 281           [AT_EXECFD - 2] =             { "EXECFD:            ", dec },
 282           [AT_EXECFN - 2] =             { "EXECFN:            ", str },
 283           [AT_PHDR - 2] =               { "PHDR:              0x", hex },
 284           [AT_PHENT - 2] =              { "PHENT:             ", dec },
 285           [AT_PHNUM - 2] =              { "PHNUM:             ", dec },
 286           [AT_PAGESZ - 2] =             { "PAGESZ:            ", dec },
 287           [AT_BASE - 2] =               { "BASE:              0x", hex },
 288           [AT_FLAGS - 2] =              { "FLAGS:             0x", hex },
 289           [AT_ENTRY - 2] =              { "ENTRY:             0x", hex },
 290           [AT_NOTELF - 2] =             { "NOTELF:            ", hex },
 291           [AT_UID - 2] =                { "UID:               ", dec },
 292           [AT_EUID - 2] =               { "EUID:              ", dec },
 293           [AT_GID - 2] =                { "GID:               ", dec },
 294           [AT_EGID - 2] =               { "EGID:              ", dec },
 295           [AT_PLATFORM - 2] =           { "PLATFORM:          ", str },
 296           [AT_HWCAP - 2] =              { "HWCAP:             ", hex },
 297           [AT_CLKTCK - 2] =             { "CLKTCK:            ", dec },
 298           [AT_FPUCW - 2] =              { "FPUCW:             ", hex },
 299           [AT_DCACHEBSIZE - 2] =        { "DCACHEBSIZE:       0x", hex },
 300           [AT_ICACHEBSIZE - 2] =        { "ICACHEBSIZE:       0x", hex },
 301           [AT_UCACHEBSIZE - 2] =        { "UCACHEBSIZE:       0x", hex },
 302           [AT_IGNOREPPC - 2] =          { "IGNOREPPC", ignore },
 303           [AT_SECURE - 2] =             { "SECURE:            ", dec },
 304           [AT_BASE_PLATFORM - 2] =      { "BASE_PLATFORM:     ", str },
 305           [AT_SYSINFO - 2] =            { "SYSINFO:           0x", hex },
 306           [AT_SYSINFO_EHDR - 2] =       { "SYSINFO_EHDR:      0x", hex },
 307           [AT_RANDOM - 2] =             { "RANDOM:            0x", hex },
 308           [AT_HWCAP2 - 2] =             { "HWCAP2:            0x", hex },
 309           [AT_L1I_CACHESIZE - 2] =      { "L1I_CACHESIZE:     ", dec },
 310           [AT_L1I_CACHEGEOMETRY - 2] =  { "L1I_CACHEGEOMETRY: 0x", hex },
 311           [AT_L1D_CACHESIZE - 2] =      { "L1D_CACHESIZE:     ", dec },
 312           [AT_L1D_CACHEGEOMETRY - 2] =  { "L1D_CACHEGEOMETRY: 0x", hex },
 313           [AT_L2_CACHESIZE - 2] =       { "L2_CACHESIZE:      ", dec },
 314           [AT_L2_CACHEGEOMETRY - 2] =   { "L2_CACHEGEOMETRY:  0x", hex },
 315           [AT_L3_CACHESIZE - 2] =       { "L3_CACHESIZE:      ", dec },
 316           [AT_L3_CACHEGEOMETRY - 2] =   { "L3_CACHEGEOMETRY:  0x", hex },
 317         };
 318       unsigned int idx = (unsigned int) (av->a_type - 2);
 319
 320       if ((unsigned int) av->a_type < 2u
 321           || (idx < sizeof (auxvars) / sizeof (auxvars[0])
 322               && auxvars[idx].form == ignore))
 323         continue;
 324
 325       assert (AT_NULL == 0);
 326       assert (AT_IGNORE == 1);
 327
 328       /* Some entries are handled in a special way per platform.  */
 329       if (_dl_procinfo (av->a_type, av->a_un.a_val) == 0)
 330         continue;
 331
 332       if (idx < sizeof (auxvars) / sizeof (auxvars[0])
 333           && auxvars[idx].form != unknown)
 334         {
 335           const char *val = (char *) av->a_un.a_val;
 336
 337           if (__builtin_expect (auxvars[idx].form, dec) == dec)
 338             val = _itoa ((unsigned long int) av->a_un.a_val,
 339                          buf + sizeof buf - 1, 10, 0);
 340           else if (__builtin_expect (auxvars[idx].form, hex) == hex)
 341             val = _itoa ((unsigned long int) av->a_un.a_val,
 342                          buf + sizeof buf - 1, 16, 0);
 343
 344           _dl_printf ("AT_%s%s\n", auxvars[idx].label, val);
 345
 346           continue;
 347         }
 348
 349       /* Unknown value: print a generic line.  */
 350       char buf2[17];
 351       buf2[sizeof (buf2) - 1] = '\0';
 352       const char *val2 = _itoa ((unsigned long int) av->a_un.a_val,
 353                                 buf2 + sizeof buf2 - 1, 16, 0);
 354       const char *val =  _itoa ((unsigned long int) av->a_type,
 355                                 buf + sizeof buf - 1, 16, 0);
 356       _dl_printf ("AT_??? (0x%s): 0x%s\n", val, val2);
 357     }
 358 }
 359
 360 #endif