1/* Implement __enable_execute_stack using mprotect(2).
2   Copyright (C) 2011-2015 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
31static int need_enable_exec_stack;
32
33static void check_enabling (void) __attribute__ ((unused));
34extern void __enable_execute_stack (void *);
35
36#if defined __sun__ && defined __svr4__
37static void __attribute__ ((constructor))
38check_enabling (void)
39{
40  int prot = (int) sysconf (_SC_STACK_PROT);
41
42  if (prot != STACK_PROT_RWX)
43    need_enable_exec_stack = 1;
44}
45#else
46/* There is no way to query the execute permission of the stack, so
47   we always issue the mprotect() call.  */
48
49static int need_enable_exec_stack = 1;
50#endif
51
52/* Attempt to turn on access permissions for the stack.  Unfortunately it
53   is not possible to make this namespace-clean.*/
54
55void
56__enable_execute_stack (void *addr)
57{
58  if (!need_enable_exec_stack)
59    return;
60  else
61    {
62      static long size, mask;
63
64      if (size == 0) {
65	size = getpagesize ();
66	mask = ~(size - 1);
67      }
68
69      char *page = (char *) (((long) addr) & mask);
70      char *end  = (char *)
71	((((long) (addr + __LIBGCC_TRAMPOLINE_SIZE__)) & mask) + size);
72
73      if (mprotect (page, end - page, STACK_PROT_RWX) < 0)
74	/* Note that no errors should be emitted by this code; it is
75	   considered dangerous for library calls to send messages to
76	   stdout/stderr.  */
77	abort ();
78    }
79}
80