LXR linux/arch/x86/kernel/test

   1/*
   2 * test_nx.c: functional test for NX functionality
   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 <linux/sort.h>
  14#include <linux/slab.h>
  15
  16#include <asm/uaccess.h>
  17#include <asm/asm.h>
  18
  19extern int rodata_test_data;
  20
  21/*
  22 * This file checks 4 things:
  23 * 1) Check if the stack is not executable
  24 * 2) Check if kmalloc memory is not executable
  25 * 3) Check if the .rodata section is not executable
  26 * 4) Check if the .data section of a module is not executable
  27 *
  28 * To do this, the test code tries to execute memory in stack/kmalloc/etc,
  29 * and then checks if the expected trap happens.
  30 *
  31 * Sadly, this implies having a dynamic exception handling table entry.
  32 * ... which can be done (and will make Rusty cry)... but it can only
  33 * be done in a stand-alone module with only 1 entry total.
  34 * (otherwise we'd have to sort and that's just too messy)
  35 */
  36
  37
  38
  39/*
  40 * We want to set up an exception handling point on our stack,
  41 * which means a variable value. This function is rather dirty
  42 * and walks the exception table of the module, looking for a magic
  43 * marker and replaces it with a specific function.
  44 */
  45static void fudze_exception_table(void *marker, void *new)
  46{
  47        struct module *mod = THIS_MODULE;
  48        struct exception_table_entry *extable;
  49
  50        /*
  51         * Note: This module has only 1 exception table entry,
  52         * so searching and sorting is not needed. If that changes,
  53         * this would be the place to search and re-sort the exception
  54         * table.
  55         */
  56        if (mod->num_exentries > 1) {
  57                printk(KERN_ERR "test_nx: too many exception table entries!\n");
  58                printk(KERN_ERR "test_nx: test results are not reliable.\n");
  59                return;
  60        }
  61        extable = (struct exception_table_entry *)mod->extable;
  62        extable[0].insn = (unsigned long)new;
  63}
  64
  65
  66/*
  67 * exception tables get their symbols translated so we need
  68 * to use a fake function to put in there, which we can then
  69 * replace at runtime.
  70 */
  71void foo_label(void);
  72
  73/*
  74 * returns 0 for not-executable, negative for executable
  75 *
  76 * Note: we cannot allow this function to be inlined, because
  77 * that would give us more than 1 exception table entry.
  78 * This in turn would break the assumptions above.
  79 */
  80static noinline int test_address(void *address)
  81{
  82        unsigned long result;
  83
  84        /* Set up an exception table entry for our address */
  85        fudze_exception_table(&foo_label, address);
  86        result = 1;
  87        asm volatile(
  88                "foo_label:\n"
  89                "0:     call *%[fake_code]\n"
  90                "1:\n"
  91                ".section .fixup,\"ax\"\n"
  92                "2:     mov %[zero], %[rslt]\n"
  93                "       ret\n"
  94                ".previous\n"
  95                _ASM_EXTABLE(0b,2b)
  96                : [rslt] "=r" (result)
  97                : [fake_code] "r" (address), [zero] "r" (0UL), "0" (result)
  98        );
  99        /* change the exception table back for the next round */
 100        fudze_exception_table(address, &foo_label);
 101
 102        if (result)
 103                return -ENODEV;
 104        return 0;
 105}
 106
 107static unsigned char test_data = 0xC3; /* 0xC3 is the opcode for "ret" */
 108
 109static int test_NX(void)
 110{
 111        int ret = 0;
 112        /* 0xC3 is the opcode for "ret" */
 113        char stackcode[] = {0xC3, 0x90, 0 };
 114        char *heap;
 115
 116        test_data = 0xC3;
 117
 118        printk(KERN_INFO "Testing NX protection\n");
 119
 120        /* Test 1: check if the stack is not executable */
 121        if (test_address(&stackcode)) {
 122                printk(KERN_ERR "test_nx: stack was executable\n");
 123                ret = -ENODEV;
 124        }
 125
 126
 127        /* Test 2: Check if the heap is executable */
 128        heap = kmalloc(64, GFP_KERNEL);
 129        if (!heap)
 130                return -ENOMEM;
 131        heap[0] = 0xC3; /* opcode for "ret" */
 132
 133        if (test_address(heap)) {
 134                printk(KERN_ERR "test_nx: heap was executable\n");
 135                ret = -ENODEV;
 136        }
 137        kfree(heap);
 138
 139        /*
 140         * The following 2 tests currently fail, this needs to get fixed
 141         * Until then, don't run them to avoid too many people getting scared
 142         * by the error message
 143         */
 144
 145        /* Test 3: Check if the .rodata section is executable */
 146        if (rodata_test_data != 0xC3) {
 147                printk(KERN_ERR "test_nx: .rodata marker has invalid value\n");
 148                ret = -ENODEV;
 149        } else if (test_address(&rodata_test_data)) {
 150                printk(KERN_ERR "test_nx: .rodata section is executable\n");
 151                ret = -ENODEV;
 152        }
 153
 154#if 0
 155        /* Test 4: Check if the .data section of a module is executable */
 156        if (test_address(&test_data)) {
 157                printk(KERN_ERR "test_nx: .data section is executable\n");
 158                ret = -ENODEV;
 159        }
 160
 161#endif
 162        return ret;
 163}
 164
 165static void test_exit(void)
 166{
 167}
 168
 169module_init(test_NX);
 170module_exit(test_exit);
 171MODULE_LICENSE("GPL");
 172MODULE_DESCRIPTION("Testcase for the NX infrastructure");
 173MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>");
 174