root/arch/x86/kernel/test_rodata.c

DEFINITIONS

1. rodata_test

/*
 * test_rodata.c: functional test for mark_rodata_ro function
 *
 * (C) Copyright 2008 Intel Corporation
 * Author: Arjan van de Ven <arjan@linux.intel.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; version 2
 * of the License.
 */
#include <linux/module.h>
#include <asm/cacheflush.h>
#include <asm/sections.h>

int rodata_test(void)
{
        unsigned long result;
        unsigned long start, end;

        /* test 1: read the value */
        /* If this test fails, some previous testrun has clobbered the state */
        if (!rodata_test_data) {
                printk(KERN_ERR "rodata_test: test 1 fails (start data)\n");
                return -ENODEV;
        }

        /* test 2: write to the variable; this should fault */
        /*
         * If this test fails, we managed to overwrite the data
         *
         * This is written in assembly to be able to catch the
         * exception that is supposed to happen in the correct
         * case
         */

        result = 1;
        asm volatile(
                "0:     mov %[zero],(%[rodata_test])\n"
                "       mov %[zero], %[rslt]\n"
                "1:\n"
                ".section .fixup,\"ax\"\n"
                "2:     jmp 1b\n"
                ".previous\n"
                ".section __ex_table,\"a\"\n"
                "       .align 16\n"
#ifdef CONFIG_X86_32
                "       .long 0b,2b\n"
#else
                "       .quad 0b,2b\n"
#endif
                ".previous"
                : [rslt] "=r" (result)
                : [rodata_test] "r" (&rodata_test_data), [zero] "r" (0UL)
        );


        if (!result) {
                printk(KERN_ERR "rodata_test: test data was not read only\n");
                return -ENODEV;
        }

        /* test 3: check the value hasn't changed */
        /* If this test fails, we managed to overwrite the data */
        if (!rodata_test_data) {
                printk(KERN_ERR "rodata_test: Test 3 failes (end data)\n");
                return -ENODEV;
        }
        /* test 4: check if the rodata section is 4Kb aligned */
        start = (unsigned long)__start_rodata;
        end = (unsigned long)__end_rodata;
        if (start & (PAGE_SIZE - 1)) {
                printk(KERN_ERR "rodata_test: .rodata is not 4k aligned\n");
                return -ENODEV;
        }
        if (end & (PAGE_SIZE - 1)) {
                printk(KERN_ERR "rodata_test: .rodata end is not 4k aligned\n");
                return -ENODEV;
        }

        return 0;
}

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Testcase for the DEBUG_RODATA infrastructure");
MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");