arch/x86/kernel/test_rodata.c

   1 /*
   2  * test_rodata.c: functional test for mark_rodata_ro function
   3  *
   4  * (C) Copyright 2008 Intel Corporation
   5  * Author: Arjan van de Ven <arjan@linux.intel.com>
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public License
   9  * as published by the Free Software Foundation; version 2
  10  * of the License.
  11  */
  12 #include <linux/module.h>
  13 #include <asm/cacheflush.h>
  14 #include <asm/sections.h>
  15 #include <asm/asm.h>
  16
  17 int rodata_test(void)
  18 {
  19         unsigned long result;
  20         unsigned long start, end;
  21
  22         /* test 1: read the value */
  23         /* If this test fails, some previous testrun has clobbered the state */
  24         if (!rodata_test_data) {
  25                 printk(KERN_ERR "rodata_test: test 1 fails (start data)\n");
  26                 return -ENODEV;
  27         }
  28
  29         /* test 2: write to the variable; this should fault */
  30         /*
  31          * If this test fails, we managed to overwrite the data
  32          *
  33          * This is written in assembly to be able to catch the
  34          * exception that is supposed to happen in the correct
  35          * case
  36          */
  37
  38         result = 1;
  39         asm volatile(
  40                 "0:     mov %[zero],(%[rodata_test])\n"
  41                 "       mov %[zero], %[rslt]\n"
  42                 "1:\n"
  43                 ".section .fixup,\"ax\"\n"
  44                 "2:     jmp 1b\n"
  45                 ".previous\n"
  46                 _ASM_EXTABLE(0b,2b)
  47                 : [rslt] "=r" (result)
  48                 : [rodata_test] "r" (&rodata_test_data), [zero] "r" (0UL)
  49         );
  50
  51
  52         if (!result) {
  53                 printk(KERN_ERR "rodata_test: test data was not read only\n");
  54                 return -ENODEV;
  55         }
  56
  57         /* test 3: check the value hasn't changed */
  58         /* If this test fails, we managed to overwrite the data */
  59         if (!rodata_test_data) {
  60                 printk(KERN_ERR "rodata_test: Test 3 failes (end data)\n");
  61                 return -ENODEV;
  62         }
  63         /* test 4: check if the rodata section is 4Kb aligned */
  64         start = (unsigned long)__start_rodata;
  65         end = (unsigned long)__end_rodata;
  66         if (start & (PAGE_SIZE - 1)) {
  67                 printk(KERN_ERR "rodata_test: .rodata is not 4k aligned\n");
  68                 return -ENODEV;
  69         }
  70         if (end & (PAGE_SIZE - 1)) {
  71                 printk(KERN_ERR "rodata_test: .rodata end is not 4k aligned\n");
  72                 return -ENODEV;
  73         }
  74
  75         return 0;
  76 }
  77
  78 MODULE_LICENSE("GPL");
  79 MODULE_DESCRIPTION("Testcase for the DEBUG_RODATA infrastructure");
  80 MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");