arch/x86/kernel/test_nx.c

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