elf/tst-execstack.c

   1 /* Test program for making nonexecutable stacks executable
   2    on load of a DSO that requires executable stacks.  */
   3
   4 #include <dlfcn.h>
   5 #include <stdbool.h>
   6 #include <stdio.h>
   7 #include <string.h>
   8 #include <unistd.h>
   9 #include <error.h>
  10 #include <stackinfo.h>
  11
  12 static void
  13 print_maps (void)
  14 {
  15 #if 0
  16   char *cmd = NULL;
  17   asprintf (&cmd, "cat /proc/%d/maps", getpid ());
  18   system (cmd);
  19   free (cmd);
  20 #endif
  21 }
  22
  23 static void deeper (void (*f) (void));
  24
  25 #if USE_PTHREADS
  26 # include <pthread.h>
  27
  28 static void *
  29 tryme_thread (void *f)
  30 {
  31   (*((void (*) (void)) f)) ();
  32
  33   return 0;
  34 }
  35
  36 static pthread_barrier_t startup_barrier, go_barrier;
  37 static void *
  38 waiter_thread (void *arg)
  39 {
  40   void **f = arg;
  41   pthread_barrier_wait (&startup_barrier);
  42   pthread_barrier_wait (&go_barrier);
  43
  44   (*((void (*) (void)) *f)) ();
  45
  46   return 0;
  47 }
  48 #endif
  49
  50 static bool allow_execstack = true;
  51
  52
  53 static int
  54 do_test (void)
  55 {
  56   /* Check whether SELinux is enabled and disallows executable stacks.  */
  57   FILE *fp = fopen ("/selinux/enforce", "r");
  58   if (fp != NULL)
  59     {
  60       char *line = NULL;
  61       size_t linelen = 0;
  62
  63       bool enabled = false;
  64       ssize_t n = getline (&line, &linelen, fp);
  65       if (n > 0 && line[0] != '0')
  66         enabled = true;
  67
  68       fclose (fp);
  69
  70       if (enabled)
  71         {
  72           fp = fopen ("/selinux/booleans/allow_execstack", "r");
  73           if (fp != NULL)
  74             {
  75               n = getline (&line, &linelen, fp);
  76               if (n > 0 && line[0] == '0')
  77                 allow_execstack = false;
  78             }
  79
  80           fclose (fp);
  81         }
  82     }
  83
  84   printf ("executable stacks %sallowed\n", allow_execstack ? "" : "not ");
  85
  86   static void *f;               /* Address of this is used in other threads. */
  87
  88 #if USE_PTHREADS
  89   /* Create some threads while stacks are nonexecutable.  */
  90   #define N 5
  91   pthread_t thr[N];
  92
  93   pthread_barrier_init (&startup_barrier, NULL, N + 1);
  94   pthread_barrier_init (&go_barrier, NULL, N + 1);
  95
  96   for (int i = 0; i < N; ++i)
  97     {
  98       int rc = pthread_create (&thr[i], NULL, &waiter_thread, &f);
  99       if (rc)
 100         error (1, rc, "pthread_create");
 101     }
 102
 103   /* Make sure they are all there using their stacks.  */
 104   pthread_barrier_wait (&startup_barrier);
 105   puts ("threads waiting");
 106 #endif
 107
 108   print_maps ();
 109
 110 #if USE_PTHREADS
 111   void *old_stack_addr, *new_stack_addr;
 112   size_t stack_size;
 113   pthread_t me = pthread_self ();
 114   pthread_attr_t attr;
 115   int ret = 0;
 116
 117   ret = pthread_getattr_np (me, &attr);
 118   if (ret)
 119     {
 120       printf ("before execstack: pthread_getattr_np returned error: %s\n",
 121               strerror (ret));
 122       return 1;
 123     }
 124
 125   ret = pthread_attr_getstack (&attr, &old_stack_addr, &stack_size);
 126   if (ret)
 127     {
 128       printf ("before execstack: pthread_attr_getstack returned error: %s\n",
 129               strerror (ret));
 130       return 1;
 131     }
 132 # if _STACK_GROWS_DOWN
 133     old_stack_addr += stack_size;
 134 # else
 135     old_stack_addr -= stack_size;
 136 # endif
 137 #endif
 138
 139   /* Loading this module should force stacks to become executable.  */
 140   void *h = dlopen ("tst-execstack-mod.so", RTLD_LAZY);
 141   if (h == NULL)
 142     {
 143       printf ("cannot load: %s\n", dlerror ());
 144       return allow_execstack;
 145     }
 146
 147   f = dlsym (h, "tryme");
 148   if (f == NULL)
 149     {
 150       printf ("symbol not found: %s\n", dlerror ());
 151       return 1;
 152     }
 153
 154   /* Test if that really made our stack executable.
 155      The `tryme' function should crash if not.  */
 156
 157   (*((void (*) (void)) f)) ();
 158
 159   print_maps ();
 160
 161 #if USE_PTHREADS
 162   ret = pthread_getattr_np (me, &attr);
 163   if (ret)
 164     {
 165       printf ("after execstack: pthread_getattr_np returned error: %s\n",
 166               strerror (ret));
 167       return 1;
 168     }
 169
 170   ret = pthread_attr_getstack (&attr, &new_stack_addr, &stack_size);
 171   if (ret)
 172     {
 173       printf ("after execstack: pthread_attr_getstack returned error: %s\n",
 174               strerror (ret));
 175       return 1;
 176     }
 177
 178 # if _STACK_GROWS_DOWN
 179     new_stack_addr += stack_size;
 180 # else
 181     new_stack_addr -= stack_size;
 182 # endif
 183
 184   /* It is possible that the dlopen'd module may have been mmapped just below
 185      the stack.  The stack size is taken as MIN(stack rlimit size, end of last
 186      vma) in pthread_getattr_np.  If rlimit is set high enough, it is possible
 187      that the size may have changed.  A subsequent call to
 188      pthread_attr_getstack returns the size and (bottom - size) as the
 189      stacksize and stackaddr respectively.  If the size changes due to the
 190      above, then both stacksize and stackaddr can change, but the stack bottom
 191      should remain the same, which is computed as stackaddr + stacksize.  */
 192   if (old_stack_addr != new_stack_addr)
 193     {
 194       printf ("Stack end changed, old: %p, new: %p\n",
 195               old_stack_addr, new_stack_addr);
 196       return 1;
 197     }
 198   printf ("Stack address remains the same: %p\n", old_stack_addr);
 199 #endif
 200
 201   /* Test that growing the stack region gets new executable pages too.  */
 202   deeper ((void (*) (void)) f);
 203
 204   print_maps ();
 205
 206 #if USE_PTHREADS
 207   /* Test that a fresh thread now gets an executable stack.  */
 208   {
 209     pthread_t th;
 210     int rc = pthread_create (&th, NULL, &tryme_thread, f);
 211     if (rc)
 212       error (1, rc, "pthread_create");
 213   }
 214
 215   puts ("threads go");
 216   /* The existing threads' stacks should have been changed.
 217      Let them run to test it.  */
 218   pthread_barrier_wait (&go_barrier);
 219
 220   pthread_exit ((void *) (long int) (! allow_execstack));
 221 #endif
 222
 223   return ! allow_execstack;
 224 }
 225
 226 static void
 227 deeper (void (*f) (void))
 228 {
 229   char stack[1100 * 1024];
 230   explicit_bzero (stack, sizeof stack);
 231   (*f) ();
 232   memfrob (stack, sizeof stack);
 233 }
 234
 235
 236 #include <support/test-driver.c>