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

   1 /* Stack executability handling for GNU dynamic linker.  Linux version.
   2    Copyright (C) 2003, 2004 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <ldsodefs.h>
  21 #include <sys/mman.h>
  22 #include <errno.h>
  23 #include <libintl.h>
  24 #include <stdbool.h>
  25 #include <stackinfo.h>
  26 #include <caller.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
  42   /* Challenge the caller.  */
  43   if (__builtin_expect (__check_caller (RETURN_ADDRESS (0),
  44                                         allow_ldso|allow_libpthread) != 0, 0)
  45       || __builtin_expect (*stack_endp != __libc_stack_end, 0))
  46     return EPERM;
  47
  48   /* Newer Linux kernels support a flag to make our job easy.  */
  49 #if defined  PROT_GROWSDOWN || defined PROT_GROWSUP
  50 # if __ASSUME_PROT_GROWSUPDOWN == 0
  51   static bool no_growsupdown;
  52   if (! no_growsupdown)
  53 # endif
  54     {
  55       if (__builtin_expect (__mprotect ((void *) page, GLRO(dl_pagesize),
  56                                         __stack_prot) == 0, 1))
  57         goto return_success;
  58 # if __ASSUME_PROT_GROWSUPDOWN == 0
  59       if (errno == EINVAL)
  60         no_growsupdown = true;
  61       else
  62 # endif
  63         return errno;
  64     }
  65 #endif
  66
  67   /* There is always a hole in the address space below the bottom of the
  68      stack.  So when we make an mprotect call that starts below the bottom
  69      of the stack, it will include the hole and fail with ENOMEM.
  70
  71      We start with a random guess at how deep the stack might have gotten
  72      so as to have extended the GROWSDOWN mapping to lower pages.  */
  73
  74 #if __ASSUME_PROT_GROWSUPDOWN == 0
  75   size_t size = GLRO(dl_pagesize) * 8;
  76
  77 # if _STACK_GROWS_DOWN
  78   page = page + GLRO(dl_pagesize) - size;
  79   while (1)
  80     {
  81       if (__mprotect ((void *) page, size,
  82                       __stack_prot & ~PROT_GROWSDOWN) == 0)
  83         /* We got this chunk changed; loop to do another chunk below.  */
  84         page -= size;
  85       else
  86         {
  87           if (errno != ENOMEM)  /* Unexpected failure mode.  */
  88             return errno;
  89
  90           if (size == GLRO(dl_pagesize))
  91             /* We just tried to mprotect the top hole page and failed.
  92                We are done.  */
  93             break;
  94
  95           /* Our mprotect call failed because it started below the lowest
  96              stack page.  Try again on just the top half of that region.  */
  97           size /= 2;
  98           page += size;
  99         }
 100     }
 101
 102 # elif _STACK_GROWS_UP
 103   while (1)
 104     {
 105       if (__mprotect ((void *) page, size, __stack_prot & ~PROT_GROWSUP) == 0)
 106         /* We got this chunk changed; loop to do another chunk below.  */
 107         page += size;
 108       else
 109         {
 110           if (errno != ENOMEM)  /* Unexpected failure mode.  */
 111             return errno;
 112
 113           if (size == GLRO(dl_pagesize))
 114             /* We just tried to mprotect the lowest hole page and failed.
 115                We are done.  */
 116             break;
 117
 118           /* Our mprotect call failed because it extended past the highest
 119              stack page.  Try again on just the bottom half of that region.  */
 120           size /= 2;
 121         }
 122     }
 123
 124 # else
 125 #  error "Define either _STACK_GROWS_DOWN or _STACK_GROWS_UP"
 126 # endif
 127 #endif
 128
 129  return_success:
 130   /* Clear the address.  */
 131   *stack_endp = NULL;
 132
 133   /* Remember that we changed the permission.  */
 134   GL(dl_stack_flags) |= PF_X;
 135
 136   return 0;
 137 }
 138 rtld_hidden_def (_dl_make_stack_executable)