sysdeps/unix/sysv/linux/dl-execstack.c

   1 /* Stack executability handling for GNU dynamic linker.  Linux version.
   2    Copyright (C) 2003-2024 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 <errno.h>
  20 #include <ldsodefs.h>
  21 #include <libintl.h>
  22 #include <list.h>
  23 #include <pthreadP.h>
  24 #include <stackinfo.h>
  25 #include <stdbool.h>
  26 #include <sys/mman.h>
  27 #include <sysdep.h>
  28 #include <unistd.h>
  29
  30 extern int __stack_prot attribute_relro attribute_hidden;
  31
  32 static int
  33 make_main_stack_executable (void **stack_endp)
  34 {
  35   /* This gives us the highest/lowest page that needs to be changed.  */
  36   uintptr_t page = ((uintptr_t) *stack_endp
  37                     & -(intptr_t) GLRO(dl_pagesize));
  38   int result = 0;
  39
  40   if (__builtin_expect (__mprotect ((void *) page, GLRO(dl_pagesize),
  41                                     __stack_prot) == 0, 1))
  42     goto return_success;
  43   result = errno;
  44   goto out;
  45
  46  return_success:
  47   /* Clear the address.  */
  48   *stack_endp = NULL;
  49
  50   /* Remember that we changed the permission.  */
  51   GL(dl_stack_flags) |= PF_X;
  52
  53  out:
  54 #ifdef check_consistency
  55   check_consistency ();
  56 #endif
  57
  58   return result;
  59 }
  60
  61 int
  62 _dl_make_stacks_executable (void **stack_endp)
  63 {
  64   /* First the main thread's stack.  */
  65   int err = make_main_stack_executable (stack_endp);
  66   if (err != 0)
  67     return err;
  68
  69   lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
  70
  71   list_t *runp;
  72   list_for_each (runp, &GL (dl_stack_used))
  73     {
  74       err = __nptl_change_stack_perm (list_entry (runp, struct pthread, list));
  75       if (err != 0)
  76         break;
  77     }
  78
  79   /* Also change the permission for the currently unused stacks.  This
  80      might be wasted time but better spend it here than adding a check
  81      in the fast path.  */
  82   if (err == 0)
  83     list_for_each (runp, &GL (dl_stack_cache))
  84       {
  85         err = __nptl_change_stack_perm (list_entry (runp, struct pthread,
  86                                                     list));
  87         if (err != 0)
  88           break;
  89       }
  90
  91   lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
  92
  93   return err;
  94 }
  95
  96 int
  97 __nptl_change_stack_perm (struct pthread *pd)
  98 {
  99 #if _STACK_GROWS_DOWN
 100   void *stack = pd->stackblock + pd->guardsize;
 101   size_t len = pd->stackblock_size - pd->guardsize;
 102 #elif _STACK_GROWS_UP
 103   void *stack = pd->stackblock;
 104   size_t len = (uintptr_t) pd - pd->guardsize - (uintptr_t) pd->stackblock;
 105 #else
 106 # error "Define either _STACK_GROWS_DOWN or _STACK_GROWS_UP"
 107 #endif
 108   if (__mprotect (stack, len, PROT_READ | PROT_WRITE | PROT_EXEC) != 0)
 109     return errno;
 110
 111   return 0;
 112 }
 113 rtld_hidden_def (__nptl_change_stack_perm)