elf/dl-fptr.c

   1 /* Manage function descriptors.  Generic version.
   2    Copyright (C) 1999-2022 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 #include <libintl.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22 #include <sys/param.h>
  23 #include <sys/mman.h>
  24 #include <link.h>
  25 #include <ldsodefs.h>
  26 #include <elf/dynamic-link.h>
  27 #include <dl-fptr.h>
  28 #include <dl-unmap-segments.h>
  29 #include <atomic.h>
  30
  31 #ifndef ELF_MACHINE_BOOT_FPTR_TABLE_LEN
  32 /* ELF_MACHINE_BOOT_FPTR_TABLE_LEN should be greater than the number of
  33    dynamic symbols in ld.so.  */
  34 # define ELF_MACHINE_BOOT_FPTR_TABLE_LEN 256
  35 #endif
  36
  37 #ifndef ELF_MACHINE_LOAD_ADDRESS
  38 # error "ELF_MACHINE_LOAD_ADDRESS is not defined."
  39 #endif
  40
  41 #ifndef COMPARE_AND_SWAP
  42 # define COMPARE_AND_SWAP(ptr, old, new) \
  43   (catomic_compare_and_exchange_bool_acq (ptr, new, old) == 0)
  44 #endif
  45
  46 ElfW(Addr) _dl_boot_fptr_table [ELF_MACHINE_BOOT_FPTR_TABLE_LEN];
  47
  48 static struct local
  49   {
  50     struct fdesc_table *root;
  51     struct fdesc *free_list;
  52     unsigned int npages;                /* # of pages to allocate */
  53     /* the next to members MUST be consecutive! */
  54     struct fdesc_table boot_table;
  55     struct fdesc boot_fdescs[1024];
  56   }
  57 local =
  58   {
  59     .root = &local.boot_table,
  60     .npages = 2,
  61     .boot_table =
  62       {
  63         .len = sizeof (local.boot_fdescs) / sizeof (local.boot_fdescs[0]),
  64         .first_unused = 0
  65       }
  66   };
  67
  68 /* Create a new fdesc table and return a pointer to the first fdesc
  69    entry.  The fdesc lock must have been acquired already.  */
  70
  71 static struct fdesc_table *
  72 new_fdesc_table (struct local *l, size_t *size)
  73 {
  74   size_t old_npages = l->npages;
  75   size_t new_npages = old_npages + old_npages;
  76   struct fdesc_table *new_table;
  77
  78   /* If someone has just created a new table, we return NULL to tell
  79      the caller to use the new table.  */
  80   if (! COMPARE_AND_SWAP (&l->npages, old_npages, new_npages))
  81     return (struct fdesc_table *) NULL;
  82
  83   *size = old_npages * GLRO(dl_pagesize);
  84   new_table = __mmap (NULL, *size,
  85                       PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
  86   if (new_table == MAP_FAILED)
  87     _dl_signal_error (errno, NULL, NULL,
  88                       N_("cannot map pages for fdesc table"));
  89
  90   new_table->len
  91     = (*size - sizeof (*new_table)) / sizeof (struct fdesc);
  92   new_table->first_unused = 1;
  93   return new_table;
  94 }
  95
  96
  97 static ElfW(Addr)
  98 make_fdesc (ElfW(Addr) ip, ElfW(Addr) gp)
  99 {
 100   struct fdesc *fdesc = NULL;
 101   struct fdesc_table *root;
 102   unsigned int old;
 103   struct local *l;
 104
 105   ELF_MACHINE_LOAD_ADDRESS (l, local);
 106
 107  retry:
 108   root = l->root;
 109   while (1)
 110     {
 111       old = root->first_unused;
 112       if (old >= root->len)
 113         break;
 114       else if (COMPARE_AND_SWAP (&root->first_unused, old, old + 1))
 115         {
 116           fdesc = &root->fdesc[old];
 117           goto install;
 118         }
 119     }
 120
 121   if (l->free_list)
 122     {
 123       /* Get it from free-list.  */
 124       do
 125         {
 126           fdesc = l->free_list;
 127           if (fdesc == NULL)
 128             goto retry;
 129         }
 130       while (! COMPARE_AND_SWAP ((ElfW(Addr) *) &l->free_list,
 131                                  (ElfW(Addr)) fdesc, fdesc->ip));
 132     }
 133   else
 134     {
 135       /* Create a new fdesc table.  */
 136       size_t size;
 137       struct fdesc_table *new_table = new_fdesc_table (l, &size);
 138
 139       if (new_table == NULL)
 140         goto retry;
 141
 142       new_table->next = root;
 143       if (! COMPARE_AND_SWAP ((ElfW(Addr) *) &l->root,
 144                               (ElfW(Addr)) root,
 145                               (ElfW(Addr)) new_table))
 146         {
 147           /* Someone has just installed a new table. Return NULL to
 148              tell the caller to use the new table.  */
 149           __munmap (new_table, size);
 150           goto retry;
 151         }
 152
 153       /* Note that the first entry was reserved while allocating the
 154          memory for the new page.  */
 155       fdesc = &new_table->fdesc[0];
 156     }
 157
 158  install:
 159   fdesc->ip = ip;
 160   fdesc->gp = gp;
 161
 162   return (ElfW(Addr)) fdesc;
 163 }
 164
 165
 166 static inline ElfW(Addr) * __attribute__ ((always_inline))
 167 make_fptr_table (struct link_map *map)
 168 {
 169   const ElfW(Sym) *symtab
 170     = (const void *) D_PTR (map, l_info[DT_SYMTAB]);
 171   const char *strtab = (const void *) D_PTR (map, l_info[DT_STRTAB]);
 172   ElfW(Addr) *fptr_table;
 173   size_t size;
 174   size_t len;
 175
 176   /* XXX Apparently the only way to find out the size of the dynamic
 177      symbol section is to assume that the string table follows right
 178      afterwards...  */
 179   len = ((strtab - (char *) symtab)
 180          / map->l_info[DT_SYMENT]->d_un.d_val);
 181   size = ((len * sizeof (fptr_table[0]) + GLRO(dl_pagesize) - 1)
 182           & -GLRO(dl_pagesize));
 183   /* XXX We don't support here in the moment systems without MAP_ANON.
 184      There probably are none for IA-64.  In case this is proven wrong
 185      we will have to open /dev/null here and use the file descriptor
 186      instead of the hard-coded -1.  */
 187   fptr_table = __mmap (NULL, size,
 188                        PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE,
 189                        -1, 0);
 190   if (fptr_table == MAP_FAILED)
 191     _dl_signal_error (errno, NULL, NULL,
 192                       N_("cannot map pages for fptr table"));
 193
 194   if (COMPARE_AND_SWAP ((ElfW(Addr) *) &map->l_mach.fptr_table,
 195                         (ElfW(Addr)) NULL, (ElfW(Addr)) fptr_table))
 196     map->l_mach.fptr_table_len = len;
 197   else
 198     __munmap (fptr_table, len * sizeof (fptr_table[0]));
 199
 200   return map->l_mach.fptr_table;
 201 }
 202
 203
 204 ElfW(Addr)
 205 _dl_make_fptr (struct link_map *map, const ElfW(Sym) *sym,
 206                ElfW(Addr) ip)
 207 {
 208   ElfW(Addr) *ftab = map->l_mach.fptr_table;
 209   const ElfW(Sym) *symtab;
 210   Elf_Symndx symidx;
 211   struct local *l;
 212
 213   if (__glibc_unlikely (ftab == NULL))
 214     ftab = make_fptr_table (map);
 215
 216   symtab = (const void *) D_PTR (map, l_info[DT_SYMTAB]);
 217   symidx = sym - symtab;
 218
 219   if (symidx >= map->l_mach.fptr_table_len)
 220     _dl_signal_error (0, NULL, NULL,
 221                       N_("internal error: symidx out of range of fptr table"));
 222
 223   while (ftab[symidx] == 0)
 224     {
 225       /* GOT has already been relocated in elf_get_dynamic_info -
 226          don't try to relocate it again.  */
 227       ElfW(Addr) fdesc
 228         = make_fdesc (ip, map->l_info[DT_PLTGOT]->d_un.d_ptr);
 229
 230       if (__builtin_expect (COMPARE_AND_SWAP (&ftab[symidx], (ElfW(Addr)) NULL,
 231                                               fdesc), 1))
 232         {
 233           /* Noone has updated the entry and the new function
 234              descriptor has been installed.  */
 235 #if 0
 236           const char *strtab
 237             = (const void *) D_PTR (map, l_info[DT_STRTAB]);
 238
 239           ELF_MACHINE_LOAD_ADDRESS (l, local);
 240           if (l->root != &l->boot_table
 241               || l->boot_table.first_unused > 20)
 242             _dl_debug_printf ("created fdesc symbol `%s' at %lx\n",
 243                               strtab + sym->st_name, ftab[symidx]);
 244 #endif
 245           break;
 246         }
 247       else
 248         {
 249           /* We created a duplicated function descriptor. We put it on
 250              free-list.  */
 251           struct fdesc *f = (struct fdesc *) fdesc;
 252
 253           ELF_MACHINE_LOAD_ADDRESS (l, local);
 254
 255           do
 256             f->ip = (ElfW(Addr)) l->free_list;
 257           while (! COMPARE_AND_SWAP ((ElfW(Addr) *) &l->free_list,
 258                                      f->ip, fdesc));
 259         }
 260     }
 261
 262   return ftab[symidx];
 263 }
 264
 265
 266 void
 267 _dl_unmap (struct link_map *map)
 268 {
 269   ElfW(Addr) *ftab = map->l_mach.fptr_table;
 270   struct fdesc *head = NULL, *tail = NULL;
 271   size_t i;
 272
 273   _dl_unmap_segments (map);
 274
 275   if (ftab == NULL)
 276     return;
 277
 278   /* String together the fdesc structures that are being freed.  */
 279   for (i = 0; i < map->l_mach.fptr_table_len; ++i)
 280     {
 281       if (ftab[i])
 282         {
 283           *(struct fdesc **) ftab[i] = head;
 284           head = (struct fdesc *) ftab[i];
 285           if (tail == NULL)
 286             tail = head;
 287         }
 288     }
 289
 290   /* Prepend the new list to the free_list: */
 291   if (tail)
 292     do
 293       tail->ip = (ElfW(Addr)) local.free_list;
 294     while (! COMPARE_AND_SWAP ((ElfW(Addr) *) &local.free_list,
 295                                tail->ip, (ElfW(Addr)) head));
 296
 297   __munmap (ftab, (map->l_mach.fptr_table_len
 298                    * sizeof (map->l_mach.fptr_table[0])));
 299
 300   map->l_mach.fptr_table = NULL;
 301 }
 302
 303
 304 ElfW(Addr)
 305 _dl_lookup_address (const void *address)
 306 {
 307   ElfW(Addr) addr = (ElfW(Addr)) address;
 308   struct fdesc_table *t;
 309   unsigned long int i;
 310
 311   for (t = local.root; t != NULL; t = t->next)
 312     {
 313       i = (struct fdesc *) addr - &t->fdesc[0];
 314       if (i < t->first_unused && addr == (ElfW(Addr)) &t->fdesc[i])
 315         {
 316           addr = t->fdesc[i].ip;
 317           break;
 318         }
 319     }
 320
 321   return addr;
 322 }