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
  11 static void
  12 print_maps (void)
  13 {
  14 #if 0
  15   char *cmd = NULL;
  16   asprintf (&cmd, "cat /proc/%d/maps", getpid ());
  17   system (cmd);
  18   free (cmd);
  19 #endif
  20 }
  21
  22 static void deeper (void (*f) (void));
  23
  24 #if USE_PTHREADS
  25 # include <pthread.h>
  26
  27 static void *
  28 tryme_thread (void *f)
  29 {
  30   (*((void (*) (void)) f)) ();
  31
  32   return 0;
  33 }
  34
  35 static pthread_barrier_t startup_barrier, go_barrier;
  36 static void *
  37 waiter_thread (void *arg)
  38 {
  39   void **f = arg;
  40   pthread_barrier_wait (&startup_barrier);
  41   pthread_barrier_wait (&go_barrier);
  42
  43   (*((void (*) (void)) *f)) ();
  44
  45   return 0;
  46 }
  47 #endif
  48
  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   /* Loading this module should force stacks to become executable.  */
 111   void *h = dlopen ("tst-execstack-mod.so", RTLD_LAZY);
 112   if (h == NULL)
 113     {
 114       printf ("cannot load: %s\n", dlerror ());
 115       return allow_execstack;
 116     }
 117
 118   f = dlsym (h, "tryme");
 119   if (f == NULL)
 120     {
 121       printf ("symbol not found: %s\n", dlerror ());
 122       return 1;
 123     }
 124
 125   /* Test if that really made our stack executable.
 126      The `tryme' function should crash if not.  */
 127
 128   (*((void (*) (void)) f)) ();
 129
 130   print_maps ();
 131
 132   /* Test that growing the stack region gets new executable pages too.  */
 133   deeper ((void (*) (void)) f);
 134
 135   print_maps ();
 136
 137 #if USE_PTHREADS
 138   /* Test that a fresh thread now gets an executable stack.  */
 139   {
 140     pthread_t th;
 141     int rc = pthread_create (&th, NULL, &tryme_thread, f);
 142     if (rc)
 143       error (1, rc, "pthread_create");
 144   }
 145
 146   puts ("threads go");
 147   /* The existing threads' stacks should have been changed.
 148      Let them run to test it.  */
 149   pthread_barrier_wait (&go_barrier);
 150
 151   pthread_exit (! allow_execstack);
 152 #endif
 153
 154   return ! allow_execstack;
 155 }
 156
 157 static void
 158 deeper (void (*f) (void))
 159 {
 160   char stack[1100 * 1024];
 161   memfrob (stack, sizeof stack);
 162   (*f) ();
 163   memfrob (stack, sizeof stack);
 164 }
 165
 166
 167 #define TEST_FUNCTION do_test ()
 168 #include "../test-skeleton.c"