libgcc/enable-execute-stack-mprotect.c

   1 /* Implement __enable_execute_stack using mprotect(2).
   2    Copyright (C) 2011 Free Software Foundation, Inc.
   3
   4    This file is part of GCC.
   5
   6    GCC is free software; you can redistribute it and/or modify it under
   7    the terms of the GNU General Public License as published by the Free
   8    Software Foundation; either version 3, or (at your option) any later
   9    version.
  10
  11    GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12    WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14    for more details.
  15
  16    Under Section 7 of GPL version 3, you are granted additional
  17    permissions described in the GCC Runtime Library Exception, version
  18    3.1, as published by the Free Software Foundation.
  19
  20    You should have received a copy of the GNU General Public License and
  21    a copy of the GCC Runtime Library Exception along with this program;
  22    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23    <http://www.gnu.org/licenses/>.  */
  24
  25 #include <sys/mman.h>
  26 #include <unistd.h>
  27 #include <stdlib.h>
  28
  29 #define STACK_PROT_RWX (PROT_READ | PROT_WRITE | PROT_EXEC)
  30
  31 static int need_enable_exec_stack;
  32
  33 static void check_enabling (void) __attribute__ ((unused));
  34 extern void __enable_execute_stack (void *);
  35
  36 #if defined __FreeBSD__
  37 #include <sys/sysctl.h>
  38
  39 static void __attribute__ ((constructor))
  40 check_enabling (void)
  41 {
  42   int prot = 0;
  43   size_t len = sizeof (prot);
  44
  45   sysctlbyname ("kern.stackprot", &prot, &len, NULL, 0);
  46   if (prot != STACK_PROT_RWX)
  47     need_enable_exec_stack = 1;
  48 }
  49 #elif defined __sun__ && defined __svr4__
  50 static void __attribute__ ((constructor))
  51 check_enabling (void)
  52 {
  53   int prot = (int) sysconf (_SC_STACK_PROT);
  54
  55   if (prot != STACK_PROT_RWX)
  56     need_enable_exec_stack = 1;
  57 }
  58 #else
  59 /* There is no way to query the execute permission of the stack, so
  60    we always issue the mprotect() call.  */
  61
  62 static int need_enable_exec_stack = 1;
  63 #endif
  64
  65 #if defined __NetBSD__
  66 /* Note that we go out of our way to use namespace-non-invasive calls
  67    here.  Unfortunately, there is no libc-internal name for mprotect().  */
  68
  69 #include <sys/sysctl.h>
  70
  71 extern int __sysctl (int *, unsigned int, void *, size_t *, void *, size_t);
  72
  73 static int
  74 getpagesize (void)
  75 {
  76   static int size;
  77
  78   if (size == 0)
  79     {
  80       int mib[2];
  81       size_t len;
  82
  83       mib[0] = CTL_HW;
  84       mib[1] = HW_PAGESIZE;
  85       len = sizeof (size);
  86       (void) __sysctl (mib, 2, &size, &len, NULL, 0);
  87     }
  88   return size;
  89 }
  90 #endif /* __NetBSD__ */
  91
  92 /* Attempt to turn on access permissions for the stack.  Unfortunately it
  93    is not possible to make this namespace-clean.*/
  94
  95 void
  96 __enable_execute_stack (void *addr)
  97 {
  98   if (!need_enable_exec_stack)
  99     return;
 100   else
 101     {
 102       static long size, mask;
 103
 104       if (size == 0) {
 105         size = getpagesize ();
 106         mask = ~(size - 1);
 107       }
 108
 109       char *page = (char *) (((long) addr) & mask);
 110       char *end  = (char *)
 111         ((((long) (addr + __LIBGCC_TRAMPOLINE_SIZE__)) & mask) + size);
 112
 113       if (mprotect (page, end - page, STACK_PROT_RWX) < 0)
 114         /* Note that no errors should be emitted by this code; it is
 115            considered dangerous for library calls to send messages to
 116            stdout/stderr.  */
 117         abort ();
 118     }
 119 }