aboutsummaryrefslogtreecommitdiff
path: root/elf/tst-execstack.c
blob: 114f341d76cec77ca473b638d34f9f654b922dbc (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
/* Test program for making nonexecutable stacks executable
   on load of a DSO that requires executable stacks.  */

#include <dlfcn.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <error.h>
#include <stackinfo.h>

static void
print_maps (void)
{
#if 0
  char *cmd = NULL;
  asprintf (&cmd, "cat /proc/%d/maps", getpid ());
  system (cmd);
  free (cmd);
#endif
}

static void deeper (void (*f) (void));

#if USE_PTHREADS
# include <pthread.h>

static void *
tryme_thread (void *f)
{
  (*((void (*) (void)) f)) ();

  return 0;
}

static pthread_barrier_t startup_barrier, go_barrier;
static void *
waiter_thread (void *arg)
{
  void **f = arg;
  pthread_barrier_wait (&startup_barrier);
  pthread_barrier_wait (&go_barrier);

  (*((void (*) (void)) *f)) ();

  return 0;
}
#endif

static bool allow_execstack = true;


static int
do_test (void)
{
  /* Check whether SELinux is enabled and disallows executable stacks.  */
  FILE *fp = fopen ("/selinux/enforce", "r");
  if (fp != NULL)
    {
      char *line = NULL;
      size_t linelen = 0;

      bool enabled = false;
      ssize_t n = getline (&line, &linelen, fp);
      if (n > 0 && line[0] != '0')
	enabled = true;

      fclose (fp);

      if (enabled)
	{
	  fp = fopen ("/selinux/booleans/allow_execstack", "r");
	  if (fp != NULL)
	    {
	      n = getline (&line, &linelen, fp);
	      if (n > 0 && line[0] == '0')
		allow_execstack = false;
	    }

	  fclose (fp);
	}
    }

  printf ("executable stacks %sallowed\n", allow_execstack ? "" : "not ");

  static void *f;		/* Address of this is used in other threads. */

#if USE_PTHREADS
  /* Create some threads while stacks are nonexecutable.  */
  #define N 5
  pthread_t thr[N];

  pthread_barrier_init (&startup_barrier, NULL, N + 1);
  pthread_barrier_init (&go_barrier, NULL, N + 1);

  for (int i = 0; i < N; ++i)
    {
      int rc = pthread_create (&thr[i], NULL, &waiter_thread, &f);
      if (rc)
	error (1, rc, "pthread_create");
    }

  /* Make sure they are all there using their stacks.  */
  pthread_barrier_wait (&startup_barrier);
  puts ("threads waiting");
#endif

  print_maps ();

#if USE_PTHREADS
  void *old_stack_addr, *new_stack_addr;
  size_t stack_size;
  pthread_t me = pthread_self ();
  pthread_attr_t attr;
  int ret = 0;

  ret = pthread_getattr_np (me, &attr);
  if (ret)
    {
      printf ("before execstack: pthread_getattr_np returned error: %s\n",
	      strerror (ret));
      return 1;
    }

  ret = pthread_attr_getstack (&attr, &old_stack_addr, &stack_size);
  if (ret)
    {
      printf ("before execstack: pthread_attr_getstack returned error: %s\n",
	      strerror (ret));
      return 1;
    }
# if _STACK_GROWS_DOWN
    old_stack_addr += stack_size;
# else
    old_stack_addr -= stack_size;
# endif
#endif

  /* Loading this module should force stacks to become executable.  */
  void *h = dlopen ("tst-execstack-mod.so", RTLD_LAZY);
  if (h == NULL)
    {
      printf ("cannot load: %s\n", dlerror ());
      return allow_execstack;
    }

  f = dlsym (h, "tryme");
  if (f == NULL)
    {
      printf ("symbol not found: %s\n", dlerror ());
      return 1;
    }

  /* Test if that really made our stack executable.
     The `tryme' function should crash if not.  */

  (*((void (*) (void)) f)) ();

  print_maps ();

#if USE_PTHREADS
  ret = pthread_getattr_np (me, &attr);
  if (ret)
    {
      printf ("after execstack: pthread_getattr_np returned error: %s\n",
	      strerror (ret));
      return 1;
    }

  ret = pthread_attr_getstack (&attr, &new_stack_addr, &stack_size);
  if (ret)
    {
      printf ("after execstack: pthread_attr_getstack returned error: %s\n",
	      strerror (ret));
      return 1;
    }

# if _STACK_GROWS_DOWN
    new_stack_addr += stack_size;
# else
    new_stack_addr -= stack_size;
# endif

  /* It is possible that the dlopen'd module may have been mmapped just below
     the stack.  The stack size is taken as MIN(stack rlimit size, end of last
     vma) in pthread_getattr_np.  If rlimit is set high enough, it is possible
     that the size may have changed.  A subsequent call to
     pthread_attr_getstack returns the size and (bottom - size) as the
     stacksize and stackaddr respectively.  If the size changes due to the
     above, then both stacksize and stackaddr can change, but the stack bottom
     should remain the same, which is computed as stackaddr + stacksize.  */
  if (old_stack_addr != new_stack_addr)
    {
      printf ("Stack end changed, old: %p, new: %p\n",
	      old_stack_addr, new_stack_addr);
      return 1;
    }
  printf ("Stack address remains the same: %p\n", old_stack_addr);
#endif

  /* Test that growing the stack region gets new executable pages too.  */
  deeper ((void (*) (void)) f);

  print_maps ();

#if USE_PTHREADS
  /* Test that a fresh thread now gets an executable stack.  */
  {
    pthread_t th;
    int rc = pthread_create (&th, NULL, &tryme_thread, f);
    if (rc)
      error (1, rc, "pthread_create");
  }

  puts ("threads go");
  /* The existing threads' stacks should have been changed.
     Let them run to test it.  */
  pthread_barrier_wait (&go_barrier);

  pthread_exit ((void *) (long int) (! allow_execstack));
#endif

  return ! allow_execstack;
}

static void
deeper (void (*f) (void))
{
  char stack[1100 * 1024];
  memfrob (stack, sizeof stack);
  (*f) ();
  memfrob (stack, sizeof stack);
}


#include <support/test-driver.c>