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111
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1 /* Implement __enable_execute_stack using mprotect(2).
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145
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2 Copyright (C) 2011-2020 Free Software Foundation, Inc.
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111
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3
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4 This file is part of GCC.
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5
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6 GCC is free software; you can redistribute it and/or modify it under
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7 the terms of the GNU General Public License as published by the Free
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8 Software Foundation; either version 3, or (at your option) any later
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9 version.
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10
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11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
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13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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14 for more details.
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15
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16 Under Section 7 of GPL version 3, you are granted additional
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17 permissions described in the GCC Runtime Library Exception, version
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18 3.1, as published by the Free Software Foundation.
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19
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20 You should have received a copy of the GNU General Public License and
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21 a copy of the GCC Runtime Library Exception along with this program;
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22 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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23 <http://www.gnu.org/licenses/>. */
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24
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25 #include <sys/mman.h>
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26 #include <unistd.h>
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27 #include <stdlib.h>
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28
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29 #define STACK_PROT_RWX (PROT_READ | PROT_WRITE | PROT_EXEC)
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30
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31 static int need_enable_exec_stack;
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32
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33 static void check_enabling (void) __attribute__ ((unused));
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34 extern void __enable_execute_stack (void *);
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35
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36 #if defined __sun__ && defined __svr4__
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37 static void __attribute__ ((constructor))
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38 check_enabling (void)
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39 {
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40 int prot = (int) sysconf (_SC_STACK_PROT);
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41
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42 if (prot != STACK_PROT_RWX)
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43 need_enable_exec_stack = 1;
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44 }
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45 #else
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46 /* There is no way to query the execute permission of the stack, so
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47 we always issue the mprotect() call. */
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48
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49 static int need_enable_exec_stack = 1;
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50 #endif
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51
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52 /* Attempt to turn on access permissions for the stack. Unfortunately it
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53 is not possible to make this namespace-clean.*/
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54
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55 void
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56 __enable_execute_stack (void *addr)
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57 {
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58 if (!need_enable_exec_stack)
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59 return;
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60 else
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61 {
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62 static long size, mask;
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63
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64 if (size == 0) {
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65 size = getpagesize ();
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66 mask = ~(size - 1);
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67 }
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68
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69 char *page = (char *) (((long) addr) & mask);
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70 char *end = (char *)
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71 ((((long) (addr + __LIBGCC_TRAMPOLINE_SIZE__)) & mask) + size);
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72
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73 if (mprotect (page, end - page, STACK_PROT_RWX) < 0)
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74 /* Note that no errors should be emitted by this code; it is
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75 considered dangerous for library calls to send messages to
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76 stdout/stderr. */
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77 abort ();
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78 }
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79 }
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