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
  16 int rodata_test(void)
  17 {
  18         unsigned long result;
  19         unsigned long start, end;
  20
  21         /* test 1: read the value */
  22         /* If this test fails, some previous testrun has clobbered the state */
  23         if (!rodata_test_data) {
  24                 printk(KERN_ERR "rodata_test: test 1 fails (start data)\n");
  25                 return -ENODEV;
  26         }
  27
  28         /* test 2: write to the variable; this should fault */
  29         /*
  30          * If this test fails, we managed to overwrite the data
  31          *
  32          * This is written in assembly to be able to catch the
  33          * exception that is supposed to happen in the correct
  34          * case
  35          */
  36
  37         result = 1;
  38         asm volatile(
  39                 "0:     mov %[zero],(%[rodata_test])\n"
  40                 "       mov %[zero], %[rslt]\n"
  41                 "1:\n"
  42                 ".section .fixup,\"ax\"\n"
  43                 "2:     jmp 1b\n"
  44                 ".previous\n"
  45                 ".section __ex_table,\"a\"\n"
  46                 "       .align 16\n"
  47 #ifdef CONFIG_X86_32
  48                 "       .long 0b,2b\n"
  49 #else
  50                 "       .quad 0b,2b\n"
  51 #endif
  52                 ".previous"
  53                 : [rslt] "=r" (result)
  54                 : [rodata_test] "r" (&rodata_test_data), [zero] "r" (0UL)
  55         );
  56
  57
  58         if (!result) {
  59                 printk(KERN_ERR "rodata_test: test data was not read only\n");
  60                 return -ENODEV;
  61         }
  62
  63         /* test 3: check the value hasn't changed */
  64         /* If this test fails, we managed to overwrite the data */
  65         if (!rodata_test_data) {
  66                 printk(KERN_ERR "rodata_test: Test 3 failes (end data)\n");
  67                 return -ENODEV;
  68         }
  69         /* test 4: check if the rodata section is 4Kb aligned */
  70         start = (unsigned long)__start_rodata;
  71         end = (unsigned long)__end_rodata;
  72         if (start & (PAGE_SIZE - 1)) {
  73                 printk(KERN_ERR "rodata_test: .rodata is not 4k aligned\n");
  74                 return -ENODEV;
  75         }
  76         if (end & (PAGE_SIZE - 1)) {
  77                 printk(KERN_ERR "rodata_test: .rodata end is not 4k aligned\n");
  78                 return -ENODEV;
  79         }
  80
  81         return 0;
  82 }
  83
  84 MODULE_LICENSE("GPL");
  85 MODULE_DESCRIPTION("Testcase for the DEBUG_RODATA infrastructure");
  86 MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");