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

   1 /* Stack executability handling for GNU dynamic linker.  Linux version.
   2    Copyright (C) 2003, 2004, 2005, 2006 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 #include <ldsodefs.h>
  20 #include <sys/mman.h>
  21 #include <errno.h>
  22 #include <libintl.h>
  23 #include <stdbool.h>
  24 #include <stackinfo.h>
  25 #include <caller.h>
  26 #include <sysdep.h>
  27
  28 #include <kernel-features.h>
  29
  30
  31 extern int __stack_prot attribute_relro attribute_hidden;
  32
  33
  34 int
  35 internal_function
  36 _dl_make_stack_executable (void **stack_endp)
  37 {
  38   /* This gives us the highest/lowest page that needs to be changed.  */
  39   uintptr_t page = ((uintptr_t) *stack_endp
  40                     & -(intptr_t) GLRO(dl_pagesize));
  41   int result = 0;
  42
  43   /* Challenge the caller.  */
  44   if (__builtin_expect (__check_caller (RETURN_ADDRESS (0),
  45                                         allow_ldso|allow_libpthread) != 0, 0)
  46       || __builtin_expect (*stack_endp != __libc_stack_end, 0))
  47     return EPERM;
  48
  49   /* Newer Linux kernels support a flag to make our job easy.  */
  50 #if defined  PROT_GROWSDOWN || defined PROT_GROWSUP
  51 # if __ASSUME_PROT_GROWSUPDOWN == 0
  52   static bool no_growsupdown;
  53   if (! no_growsupdown)
  54 # endif
  55     {
  56       if (__builtin_expect (__mprotect ((void *) page, GLRO(dl_pagesize),
  57                                         __stack_prot) == 0, 1))
  58         goto return_success;
  59 # if __ASSUME_PROT_GROWSUPDOWN == 0
  60       if (errno == EINVAL)
  61         no_growsupdown = true;
  62       else
  63 # endif
  64         {
  65           result = errno;
  66           goto out;
  67         }
  68     }
  69 #endif
  70
  71   /* There is always a hole in the address space below the bottom of the
  72      stack.  So when we make an mprotect call that starts below the bottom
  73      of the stack, it will include the hole and fail with ENOMEM.
  74
  75      We start with a random guess at how deep the stack might have gotten
  76      so as to have extended the GROWSDOWN mapping to lower pages.  */
  77
  78 #if __ASSUME_PROT_GROWSUPDOWN == 0
  79   size_t size = GLRO(dl_pagesize) * 8;
  80
  81 # if _STACK_GROWS_DOWN
  82   page = page + GLRO(dl_pagesize) - size;
  83   while (1)
  84     {
  85       if (__mprotect ((void *) page, size,
  86                       __stack_prot & ~PROT_GROWSDOWN) == 0)
  87         /* We got this chunk changed; loop to do another chunk below.  */
  88         page -= size;
  89       else
  90         {
  91           if (errno != ENOMEM)  /* Unexpected failure mode.  */
  92             {
  93               result = errno;
  94               goto out;
  95             }
  96
  97           if (size == GLRO(dl_pagesize))
  98             /* We just tried to mprotect the top hole page and failed.
  99                We are done.  */
 100             break;
 101
 102           /* Our mprotect call failed because it started below the lowest
 103              stack page.  Try again on just the top half of that region.  */
 104           size /= 2;
 105           page += size;
 106         }
 107     }
 108
 109 # elif _STACK_GROWS_UP
 110   while (1)
 111     {
 112       if (__mprotect ((void *) page, size, __stack_prot & ~PROT_GROWSUP) == 0)
 113         /* We got this chunk changed; loop to do another chunk below.  */
 114         page += size;
 115       else
 116         {
 117           if (errno != ENOMEM)  /* Unexpected failure mode.  */
 118             {
 119               result = errno;
 120               goto out;
 121             }
 122
 123           if (size == GLRO(dl_pagesize))
 124             /* We just tried to mprotect the lowest hole page and failed.
 125                We are done.  */
 126             break;
 127
 128           /* Our mprotect call failed because it extended past the highest
 129              stack page.  Try again on just the bottom half of that region.  */
 130           size /= 2;
 131         }
 132     }
 133
 134 # else
 135 #  error "Define either _STACK_GROWS_DOWN or _STACK_GROWS_UP"
 136 # endif
 137 #endif
 138
 139  return_success:
 140   /* Clear the address.  */
 141   *stack_endp = NULL;
 142
 143   /* Remember that we changed the permission.  */
 144   GL(dl_stack_flags) |= PF_X;
 145
 146  out:
 147 #ifdef check_consistency
 148   check_consistency ();
 149 #endif
 150
 151   return result;
 152 }
 153 rtld_hidden_def (_dl_make_stack_executable)