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 <linux/slab.h>
  15
  16 #include <asm/uaccess.h>
  17 #include <asm/asm.h>
  18
  19 extern 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  */
  45 static 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  */
  71 void 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  */
  80 static 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
 107 static unsigned char test_data = 0xC3; /* 0xC3 is the opcode for "ret" */
 108
 109 static 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
 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>");