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Commit aa981a66 authored by Kees Cook's avatar Kees Cook
Browse files

lkdtm: add usercopy tests 



This adds test to detect copy_to_user/copy_from_user problems that are
protected by PAX_USERCOPY (and will be protected by HARDENED_USERCOPY).
Explicitly tests both "to" and "from" directions of heap object size
problems, heap object markings and, stack frame misalignment.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 9a49a528

drivers/misc/lkdtm_core.c

+273 −2
Original line number Diff line number Diff line
@@ -111,7 +111,14 @@ enum ctype { 
	CT_WRITE_RO,

	CT_WRITE_RO_AFTER_INIT,

	CT_WRITE_KERN,

	CT_WRAP_ATOMIC

	CT_WRAP_ATOMIC,

	CT_USERCOPY_HEAP_SIZE_TO,

	CT_USERCOPY_HEAP_SIZE_FROM,

	CT_USERCOPY_HEAP_FLAG_TO,

	CT_USERCOPY_HEAP_FLAG_FROM,

	CT_USERCOPY_STACK_FRAME_TO,

	CT_USERCOPY_STACK_FRAME_FROM,

	CT_USERCOPY_STACK_BEYOND,

};



static char* cp_name[] = {
@@ -154,7 +161,14 @@ static char* cp_type[] = { 
	"WRITE_RO",

	"WRITE_RO_AFTER_INIT",

	"WRITE_KERN",

	"WRAP_ATOMIC"

	"WRAP_ATOMIC",

	"USERCOPY_HEAP_SIZE_TO",

	"USERCOPY_HEAP_SIZE_FROM",

	"USERCOPY_HEAP_FLAG_TO",

	"USERCOPY_HEAP_FLAG_FROM",

	"USERCOPY_STACK_FRAME_TO",

	"USERCOPY_STACK_FRAME_FROM",

	"USERCOPY_STACK_BEYOND",

};



static struct jprobe lkdtm;
@@ -166,6 +180,8 @@ static char* cpoint_name; 
static char* cpoint_type;

static int cpoint_count = DEFAULT_COUNT;

static int recur_count = REC_NUM_DEFAULT;

static int alloc_size = 1024;

static size_t cache_size;



static enum cname cpoint = CN_INVALID;

static enum ctype cptype = CT_NONE;
@@ -174,7 +190,9 @@ static DEFINE_SPINLOCK(count_lock); 
static DEFINE_SPINLOCK(lock_me_up);



static u8 data_area[EXEC_SIZE];

static struct kmem_cache *bad_cache;



static const unsigned char test_text[] = "This is a test.\n";

static const unsigned long rodata = 0xAA55AA55;

static unsigned long ro_after_init __ro_after_init = 0x55AA5500;
@@ -188,6 +206,9 @@ MODULE_PARM_DESC(cpoint_type, " Crash Point Type, action to be taken on "\ 
module_param(cpoint_count, int, 0644);

MODULE_PARM_DESC(cpoint_count, " Crash Point Count, number of times the "\

				"crash point is to be hit to trigger action");

module_param(alloc_size, int, 0644);

MODULE_PARM_DESC(alloc_size, " Size of allocation for user copy tests "\

			     "(from 1 to PAGE_SIZE)");



static unsigned int jp_do_irq(unsigned int irq)

{
@@ -381,6 +402,228 @@ static void execute_user_location(void *dst) 
	func();

}



/*

 * 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(alloc_size);

	} 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,

				 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,

				 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,

				   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,

				   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 = clamp_t(int, alloc_size, 1, PAGE_SIZE);



	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);

}



static void lkdtm_do_action(enum ctype which)

{

	switch (which) {
@@ -679,6 +922,27 @@ static void lkdtm_do_action(enum ctype which) 


		return;

	}

	case CT_USERCOPY_HEAP_SIZE_TO:

		do_usercopy_heap_size(true);

		break;

	case CT_USERCOPY_HEAP_SIZE_FROM:

		do_usercopy_heap_size(false);

		break;

	case CT_USERCOPY_HEAP_FLAG_TO:

		do_usercopy_heap_flag(true);

		break;

	case CT_USERCOPY_HEAP_FLAG_FROM:

		do_usercopy_heap_flag(false);

		break;

	case CT_USERCOPY_STACK_FRAME_TO:

		do_usercopy_stack(true, true);

		break;

	case CT_USERCOPY_STACK_FRAME_FROM:

		do_usercopy_stack(false, true);

		break;

	case CT_USERCOPY_STACK_BEYOND:

		do_usercopy_stack(true, false);

		break;

	case CT_NONE:

	default:

		break;
@@ -971,6 +1235,11 @@ static int __init lkdtm_module_init(void) 
	/* Make sure we can write to __ro_after_init values during __init */

	ro_after_init |= 0xAA;



	/* Prepare cache that lacks SLAB_USERCOPY flag. */

	cache_size = clamp_t(int, alloc_size, 1, PAGE_SIZE);

	bad_cache = kmem_cache_create("lkdtm-no-usercopy", cache_size, 0,

				      0, NULL);



	/* Register debugfs interface */

	lkdtm_debugfs_root = debugfs_create_dir("provoke-crash", NULL);

	if (!lkdtm_debugfs_root) {
@@ -1022,6 +1291,8 @@ static void __exit lkdtm_module_exit(void) 
{

	debugfs_remove_recursive(lkdtm_debugfs_root);



	kmem_cache_destroy(bad_cache);



	unregister_jprobe(&lkdtm);

	pr_info("Crash point unregistered\n");

}