blob: 3f92ce07e525fd41167a64f9d7c4df1bfbe673bf [file] [log] [blame]
* test_nx.c: functional test for NX functionality
* (C) Copyright 2008 Intel Corporation
* Author: Arjan van de Ven <>
* 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 <linux/sort.h>
#include <linux/slab.h>
#include <asm/uaccess.h>
#include <asm/asm.h>
extern int rodata_test_data;
* This file checks 4 things:
* 1) Check if the stack is not executable
* 2) Check if kmalloc memory is not executable
* 3) Check if the .rodata section is not executable
* 4) Check if the .data section of a module is not executable
* To do this, the test code tries to execute memory in stack/kmalloc/etc,
* and then checks if the expected trap happens.
* Sadly, this implies having a dynamic exception handling table entry.
* ... which can be done (and will make Rusty cry)... but it can only
* be done in a stand-alone module with only 1 entry total.
* (otherwise we'd have to sort and that's just too messy)
* We want to set up an exception handling point on our stack,
* which means a variable value. This function is rather dirty
* and walks the exception table of the module, looking for a magic
* marker and replaces it with a specific function.
static void fudze_exception_table(void *marker, void *new)
struct module *mod = THIS_MODULE;
struct exception_table_entry *extable;
* Note: This module has only 1 exception table entry,
* so searching and sorting is not needed. If that changes,
* this would be the place to search and re-sort the exception
* table.
if (mod->num_exentries > 1) {
printk(KERN_ERR "test_nx: too many exception table entries!\n");
printk(KERN_ERR "test_nx: test results are not reliable.\n");
extable = (struct exception_table_entry *)mod->extable;
extable[0].insn = (unsigned long)new;
* exception tables get their symbols translated so we need
* to use a fake function to put in there, which we can then
* replace at runtime.
void foo_label(void);
* returns 0 for not-executable, negative for executable
* Note: we cannot allow this function to be inlined, because
* that would give us more than 1 exception table entry.
* This in turn would break the assumptions above.
static noinline int test_address(void *address)
unsigned long result;
/* Set up an exception table entry for our address */
fudze_exception_table(&foo_label, address);
result = 1;
asm volatile(
"0: call *%[fake_code]\n"
".section .fixup,\"ax\"\n"
"2: mov %[zero], %[rslt]\n"
" ret\n"
: [rslt] "=r" (result)
: [fake_code] "r" (address), [zero] "r" (0UL), "0" (result)
/* change the exception table back for the next round */
fudze_exception_table(address, &foo_label);
if (result)
return -ENODEV;
return 0;
static unsigned char test_data = 0xC3; /* 0xC3 is the opcode for "ret" */
static int test_NX(void)
int ret = 0;
/* 0xC3 is the opcode for "ret" */
char stackcode[] = {0xC3, 0x90, 0 };
char *heap;
test_data = 0xC3;
printk(KERN_INFO "Testing NX protection\n");
/* Test 1: check if the stack is not executable */
if (test_address(&stackcode)) {
printk(KERN_ERR "test_nx: stack was executable\n");
ret = -ENODEV;
/* Test 2: Check if the heap is executable */
heap = kmalloc(64, GFP_KERNEL);
if (!heap)
return -ENOMEM;
heap[0] = 0xC3; /* opcode for "ret" */
if (test_address(heap)) {
printk(KERN_ERR "test_nx: heap was executable\n");
ret = -ENODEV;
* The following 2 tests currently fail, this needs to get fixed
* Until then, don't run them to avoid too many people getting scared
* by the error message
/* Test 3: Check if the .rodata section is executable */
if (rodata_test_data != 0xC3) {
printk(KERN_ERR "test_nx: .rodata marker has invalid value\n");
ret = -ENODEV;
} else if (test_address(&rodata_test_data)) {
printk(KERN_ERR "test_nx: .rodata section is executable\n");
ret = -ENODEV;
#if 0
/* Test 4: Check if the .data section of a module is executable */
if (test_address(&test_data)) {
printk(KERN_ERR "test_nx: .data section is executable\n");
ret = -ENODEV;
return ret;
static void test_exit(void)
MODULE_DESCRIPTION("Testcase for the NX infrastructure");
MODULE_AUTHOR("Arjan van de Ven <>");