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#ifdef CONFIG_DEBUG_RODATA 146 /* Test 3: Check if the .rodata section is executable */ 147 if (rodata_test_data != 0xC3) { 148 printk(KERN_ERR "test_nx: .rodata marker has invalid value\n"); 149 ret = -ENODEV; 150 } else if (test_address(&rodata_test_data)) { 151 printk(KERN_ERR "test_nx: .rodata section is executable\n"); 152 ret = -ENODEV; 153 } 154#endif 155 156 return 0; 157} 158 159static void test_exit(void) 160{ 161} 162 163module_init(test_NX); 164module_exit(test_exit); 165MODULE_LICENSE("GPL"); 166MODULE_DESCRIPTION("Testcase for the NX infrastructure"); 167MODULE_AUTHOR("Arjan van de Ven <arjan@linux.intel.com>"); 168