drivers/misc/lkdtm_usercopy.c - third_party/linux - Git at Google

 /*
  * 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/sched/task_stack.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);
 }
	/*
	* 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/sched/task_stack.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);
	}