test_rodata.c

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/*
 * 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>
#include <asm/asm.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"
        _ASM_EXTABLE(0b,2b)
        : [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>");