/*
* This is for all the tests related to copy_to_user() and copy_from_user()
* hardening.
*/
#include "lkdtm.h"
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/mman.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
/*
* Many of the tests here end up using const sizes, but those would
* normally be ignored by hardened usercopy, so force the compiler
* into choosing the non-const path to make sure we trigger the
* hardened usercopy checks by added "unconst" to all the const copies,
* and making sure "cache_size" isn't optimized into a const.
*/
static volatile size_t unconst = 0;
static volatile size_t cache_size = 1024;
static struct kmem_cache *bad_cache;
static const unsigned char test_text[] = "This is a test.\n";
/*
* Instead of adding -Wno-return-local-addr, just pass the stack address
* through a function to obfuscate it from the compiler.
*/
static noinline unsigned char *trick_compiler(unsigned char *stack)
{
return stack + 0;
}
static noinline unsigned char *do_usercopy_stack_callee(int value)
{
unsigned char buf[32];
int i;
/* Exercise stack to avoid everything living in registers. */
for (i = 0; i < sizeof(buf); i++) {
buf[i] = value & 0xff;
}
return trick_compiler(buf);
}
static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
{
unsigned long user_addr;
unsigned char good_stack[32];
unsigned char *bad_stack;
int i;
/* Exercise stack to avoid everything living in registers. */
for (i = 0; i < sizeof(good_stack); i++)
good_stack[i] = test_text[i % sizeof(test_text)];
/* This is a pointer to outside our current stack frame. */
if (bad_frame) {
bad_stack = do_usercopy_stack_callee((uintptr_t)&bad_stack);
} else {
/* Put start address just inside stack. */
bad_stack = task_stack_page(current) + THREAD_SIZE;
bad_stack -= sizeof(unsigned long);
}
user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_ANONYMOUS | MAP_PRIVATE, 0);
if (user_addr >= TASK_SIZE) {
pr_warn("Failed to allocate user memory\n");
return;
}
if (to_user) {
pr_info("attempting good copy_to_user of local stack\n");
if (copy_to_user((void __user *)user_addr, good_stack,
unconst + sizeof(good_stack))) {
pr_warn("copy_to_user failed unexpectedly?!\n");
goto free_user;
}
pr_info("attempting bad copy_to_user of distant stack\n");
if (copy_to_user((void __user *)user_addr, bad_stack,
unconst + sizeof(good_stack))) {
pr_warn("copy_to_user failed, but lacked Oops\n");
goto free_user;
}
} else {
/*
* There isn't a safe way to not be protected by usercopy
* if we're going to write to another thread's stack.
*/
if (!bad_frame)
goto free_user;
pr_info("attempting good copy_from_user of local stack\n");
if (copy_from_user(good_stack, (void __user *)user_addr,
unconst + sizeof(good_stack))) {
pr_warn("copy_from_user failed unexpectedly?!\n");
goto free_user;
}
pr_info("attempting bad copy_from_user of distant stack\n");
if (copy_from_user(bad_stack, (void __user *)user_addr,
unconst + sizeof(good_stack))) {
pr_warn("copy_from_user failed, but lacked Oops\n");
goto free_user;
}
}
free_user:
vm_munmap(user_addr, PAGE_SIZE);
}
static void do_usercopy_heap_size(bool to_user)
{
unsigned long user_addr;
unsigned char *one, *two;
size_t size = unconst + 1024;
one = kmalloc(size, GFP_KERNEL);
two = kmalloc(size, GFP_KERNEL);
if (!one || !two) {
pr_warn("Failed to allocate kernel memory\n");
goto free_kernel;
}
user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_ANONYMOUS | MAP_PRIVATE, 0);
if (user_addr >= TASK_SIZE) {
pr_warn("Failed to allocate user memory\n");
goto free_kernel;
}
memset(one, 'A', size);
memset(two, 'B', size);
if (to_user) {
pr_info("attempting good copy_to_user of correct size\n");
if (copy_to_user((void __user *)user_addr, one, size)) {
pr_warn("copy_to_user failed unexpectedly?!\n");
goto free_user;
}
pr_info("attempting bad copy_to_user of too large size\n");
if (copy_to_user((void __user *)user_addr, one, 2 * size)) {
pr_warn("copy_to_user failed, but lacked Oops\n");
goto free_user;
}
} else {
pr_info("attempting good copy_from_user of correct size\n");
if (copy_from_user(one, (void __user *)user_addr, size)) {
pr_warn("copy_from_user failed unexpectedly?!\n");
goto free_user;
}
pr_info("attempting bad copy_from_user of too large size\n");
if (copy_from_user(one, (void __user *)user_addr, 2 * size)) {
pr_warn("copy_from_user failed, but lacked Oops\n");
goto free_user;
}
}
free_user:
vm_munmap(user_addr, PAGE_SIZE);
free_kernel:
kfree(one);
kfree(two);
}
static void do_usercopy_heap_flag(bool to_user)
{
unsigned long user_addr;
unsigned char *good_buf = NULL;
unsigned char *bad_buf = NULL;
/* Make sure cache was prepared. */
if (!bad_cache) {
pr_warn("Failed to allocate kernel cache\n");
return;
}
/*
* Allocate one buffer from each cache (kmalloc will have the
* SLAB_USERCOPY flag already, but "bad_cache" won't).
*/
good_buf = kmalloc(cache_size, GFP_KERNEL);
bad_buf = kmem_cache_alloc(bad_cache, GFP_KERNEL);
if (!good_buf || !bad_buf) {
pr_warn("Failed to allocate buffers from caches\n");
goto free_alloc;
}
/* Allocate user memory we'll poke at. */
user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_ANONYMOUS | MAP_PRIVATE, 0);
if (user_addr >= TASK_SIZE) {
pr_warn("Failed to allocate user memory\n");
goto free_alloc;
}
memset(good_buf, 'A', cache_size);
memset(bad_buf, 'B', cache_size);
if (to_user) {
pr_info("attempting good copy_to_user with SLAB_USERCOPY\n");
if (copy_to_user((void __user *)user_addr, good_buf,
cache_size)) {
pr_warn("copy_to_user failed unexpectedly?!\n");
goto free_user;
}
pr_info("attempting bad copy_to_user w/o SLAB_USERCOPY\n");
if (copy_to_user((void __user *)user_addr, bad_buf,
cache_size)) {
pr_warn("copy_to_user failed, but lacked Oops\n");
goto free_user;
}
} else {
pr_info("attempting good copy_from_user with SLAB_USERCOPY\n");
if (copy_from_user(good_buf, (void __user *)user_addr,
cache_size)) {
pr_warn("copy_from_user failed unexpectedly?!\n");
goto free_user;
}
pr_info("attempting bad copy_from_user w/o SLAB_USERCOPY\n");
if (copy_from_user(bad_buf, (void __user *)user_addr,
cache_size)) {
pr_warn("copy_from_user failed, but lacked Oops\n");
goto free_user;
}
}
free_user:
vm_munmap(user_addr, PAGE_SIZE);
free_alloc:
if (bad_buf)
kmem_cache_free(bad_cache, bad_buf);
kfree(good_buf);
}
/* Callable tests. */
void lkdtm_USERCOPY_HEAP_SIZE_TO(void)
{
do_usercopy_heap_size(true);
}
void lkdtm_USERCOPY_HEAP_SIZE_FROM(void)
{
do_usercopy_heap_size(false);
}
void lkdtm_USERCOPY_HEAP_FLAG_TO(void)
{
do_usercopy_heap_flag(true);
}
void lkdtm_USERCOPY_HEAP_FLAG_FROM(void)
{
do_usercopy_heap_flag(false);
}
void lkdtm_USERCOPY_STACK_FRAME_TO(void)
{
do_usercopy_stack(true, true);
}
void lkdtm_USERCOPY_STACK_FRAME_FROM(void)
{
do_usercopy_stack(false, true);
}
void lkdtm_USERCOPY_STACK_BEYOND(void)
{
do_usercopy_stack(true, false);
}
void lkdtm_USERCOPY_KERNEL(void)
{
unsigned long user_addr;
user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_ANONYMOUS | MAP_PRIVATE, 0);
if (user_addr >= TASK_SIZE) {
pr_warn("Failed to allocate user memory\n");
return;
}
pr_info("attempting good copy_to_user from kernel rodata\n");
if (copy_to_user((void __user *)user_addr, test_text,
unconst + sizeof(test_text))) {
pr_warn("copy_to_user failed unexpectedly?!\n");
goto free_user;
}
pr_info("attempting bad copy_to_user from kernel text\n");
if (copy_to_user((void __user *)user_addr, vm_mmap,
unconst + PAGE_SIZE)) {
pr_warn("copy_to_user failed, but lacked Oops\n");
goto free_user;
}
free_user:
vm_munmap(user_addr, PAGE_SIZE);
}
void __init lkdtm_usercopy_init(void)
{
/* Prepare cache that lacks SLAB_USERCOPY flag. */
bad_cache = kmem_cache_create("lkdtm-no-usercopy", cache_size, 0,
0, NULL);
}
void __exit lkdtm_usercopy_exit(void)
{
kmem_cache_destroy(bad_cache);
}
