drivers/misc/lkdtm/usercopy.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * 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;
 static volatile size_t cache_size = 1024;
 static struct kmem_cache *whitelist_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);
 }

 /*
  * This checks for whole-object size validation with hardened usercopy,
  * with or without usercopy whitelisting.
  */
 static void do_usercopy_heap_size(bool to_user)
 {
 	unsigned long user_addr;
 	unsigned char *one, *two;
 	void __user *test_user_addr;
 	void *test_kern_addr;
 	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);

 	test_user_addr = (void __user *)(user_addr + 16);
 	test_kern_addr = one + 16;

 	if (to_user) {
 		pr_info("attempting good copy_to_user of correct size\n");
 		if (copy_to_user(test_user_addr, test_kern_addr, size / 2)) {
 			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(test_user_addr, test_kern_addr, 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(test_kern_addr, test_user_addr, size / 2)) {
 			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(test_kern_addr, test_user_addr, 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);
 }

 /*
  * This checks for the specific whitelist window within an object. If this
  * test passes, then do_usercopy_heap_size() tests will pass too.
  */
 static void do_usercopy_heap_whitelist(bool to_user)
 {
 	unsigned long user_alloc;
 	unsigned char *buf = NULL;
 	unsigned char __user *user_addr;
 	size_t offset, size;

 	/* Make sure cache was prepared. */
 	if (!whitelist_cache) {
 		pr_warn("Failed to allocate kernel cache\n");
 		return;
 	}

 	/*
 	 * Allocate a buffer with a whitelisted window in the buffer.
 	 */
 	buf = kmem_cache_alloc(whitelist_cache, GFP_KERNEL);
 	if (!buf) {
 		pr_warn("Failed to allocate buffer from whitelist cache\n");
 		goto free_alloc;
 	}

 	/* Allocate user memory we'll poke at. */
 	user_alloc = vm_mmap(NULL, 0, PAGE_SIZE,
 			    PROT_READ | PROT_WRITE | PROT_EXEC,
 			    MAP_ANONYMOUS | MAP_PRIVATE, 0);
 	if (user_alloc >= TASK_SIZE) {
 		pr_warn("Failed to allocate user memory\n");
 		goto free_alloc;
 	}
 	user_addr = (void __user *)user_alloc;

 	memset(buf, 'B', cache_size);

 	/* Whitelisted window in buffer, from kmem_cache_create_usercopy. */
 	offset = (cache_size / 4) + unconst;
 	size = (cache_size / 16) + unconst;

 	if (to_user) {
 		pr_info("attempting good copy_to_user inside whitelist\n");
 		if (copy_to_user(user_addr, buf + offset, size)) {
 			pr_warn("copy_to_user failed unexpectedly?!\n");
 			goto free_user;
 		}

 		pr_info("attempting bad copy_to_user outside whitelist\n");
 		if (copy_to_user(user_addr, buf + offset - 1, size)) {
 			pr_warn("copy_to_user failed, but lacked Oops\n");
 			goto free_user;
 		}
 	} else {
 		pr_info("attempting good copy_from_user inside whitelist\n");
 		if (copy_from_user(buf + offset, user_addr, size)) {
 			pr_warn("copy_from_user failed unexpectedly?!\n");
 			goto free_user;
 		}

 		pr_info("attempting bad copy_from_user outside whitelist\n");
 		if (copy_from_user(buf + offset - 1, user_addr, size)) {
 			pr_warn("copy_from_user failed, but lacked Oops\n");
 			goto free_user;
 		}
 	}

 free_user:
 	vm_munmap(user_alloc, PAGE_SIZE);
 free_alloc:
 	if (buf)
 		kmem_cache_free(whitelist_cache, 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_WHITELIST_TO(void)
 {
 	do_usercopy_heap_whitelist(true);
 }

 void lkdtm_USERCOPY_HEAP_WHITELIST_FROM(void)
 {
 	do_usercopy_heap_whitelist(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 lkdtm_USERCOPY_KERNEL_DS(void)
 {
 	char __user *user_ptr =
 		(char __user *)(0xFUL << (sizeof(unsigned long) * 8 - 4));
 	mm_segment_t old_fs = get_fs();
 	char buf[10] = {0};

 	pr_info("attempting copy_to_user() to noncanonical address: %px\n",
 		user_ptr);
 	set_fs(KERNEL_DS);
 	if (copy_to_user(user_ptr, buf, sizeof(buf)) == 0)
 		pr_err("copy_to_user() to noncanonical address succeeded!?\n");
 	set_fs(old_fs);
 }

 void __init lkdtm_usercopy_init(void)
 {
 	/* Prepare cache that lacks SLAB_USERCOPY flag. */
 	whitelist_cache =
 		kmem_cache_create_usercopy("lkdtm-usercopy", cache_size,
 					   0, 0,
 					   cache_size / 4,
 					   cache_size / 16,
 					   NULL);
 }

 void __exit lkdtm_usercopy_exit(void)
 {
 	kmem_cache_destroy(whitelist_cache);
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* 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;
	static volatile size_t cache_size = 1024;
	static struct kmem_cache *whitelist_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);
	}

	/*
	* This checks for whole-object size validation with hardened usercopy,
	* with or without usercopy whitelisting.
	*/
	static void do_usercopy_heap_size(bool to_user)
	{
	unsigned long user_addr;
	unsigned char one, two;
	void __user *test_user_addr;
	void *test_kern_addr;
	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);

	test_user_addr = (void __user *)(user_addr + 16);
	test_kern_addr = one + 16;

	if (to_user) {
	pr_info("attempting good copy_to_user of correct size\n");
	if (copy_to_user(test_user_addr, test_kern_addr, size / 2)) {
	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(test_user_addr, test_kern_addr, 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(test_kern_addr, test_user_addr, size / 2)) {
	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(test_kern_addr, test_user_addr, 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);
	}

	/*
	* This checks for the specific whitelist window within an object. If this
	* test passes, then do_usercopy_heap_size() tests will pass too.
	*/
	static void do_usercopy_heap_whitelist(bool to_user)
	{
	unsigned long user_alloc;
	unsigned char *buf = NULL;
	unsigned char __user *user_addr;
	size_t offset, size;

	/* Make sure cache was prepared. */
	if (!whitelist_cache) {
	pr_warn("Failed to allocate kernel cache\n");
	return;
	}

	/*
	* Allocate a buffer with a whitelisted window in the buffer.
	*/
	buf = kmem_cache_alloc(whitelist_cache, GFP_KERNEL);
	if (!buf) {
	pr_warn("Failed to allocate buffer from whitelist cache\n");
	goto free_alloc;
	}

	/* Allocate user memory we'll poke at. */
	user_alloc = vm_mmap(NULL, 0, PAGE_SIZE,
	PROT_READ \| PROT_WRITE \| PROT_EXEC,
	MAP_ANONYMOUS \| MAP_PRIVATE, 0);
	if (user_alloc >= TASK_SIZE) {
	pr_warn("Failed to allocate user memory\n");
	goto free_alloc;
	}
	user_addr = (void __user *)user_alloc;

	memset(buf, 'B', cache_size);

	/* Whitelisted window in buffer, from kmem_cache_create_usercopy. */
	offset = (cache_size / 4) + unconst;
	size = (cache_size / 16) + unconst;

	if (to_user) {
	pr_info("attempting good copy_to_user inside whitelist\n");
	if (copy_to_user(user_addr, buf + offset, size)) {
	pr_warn("copy_to_user failed unexpectedly?!\n");
	goto free_user;
	}

	pr_info("attempting bad copy_to_user outside whitelist\n");
	if (copy_to_user(user_addr, buf + offset - 1, size)) {
	pr_warn("copy_to_user failed, but lacked Oops\n");
	goto free_user;
	}
	} else {
	pr_info("attempting good copy_from_user inside whitelist\n");
	if (copy_from_user(buf + offset, user_addr, size)) {
	pr_warn("copy_from_user failed unexpectedly?!\n");
	goto free_user;
	}

	pr_info("attempting bad copy_from_user outside whitelist\n");
	if (copy_from_user(buf + offset - 1, user_addr, size)) {
	pr_warn("copy_from_user failed, but lacked Oops\n");
	goto free_user;
	}
	}

	free_user:
	vm_munmap(user_alloc, PAGE_SIZE);
	free_alloc:
	if (buf)
	kmem_cache_free(whitelist_cache, 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_WHITELIST_TO(void)
	{
	do_usercopy_heap_whitelist(true);
	}

	void lkdtm_USERCOPY_HEAP_WHITELIST_FROM(void)
	{
	do_usercopy_heap_whitelist(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 lkdtm_USERCOPY_KERNEL_DS(void)
	{
	char __user *user_ptr =
	(char __user )(0xFUL << (sizeof(unsigned long) 8 - 4));
	mm_segment_t old_fs = get_fs();
	char buf[10] = {0};

	pr_info("attempting copy_to_user() to noncanonical address: %px\n",
	user_ptr);
	set_fs(KERNEL_DS);
	if (copy_to_user(user_ptr, buf, sizeof(buf)) == 0)
	pr_err("copy_to_user() to noncanonical address succeeded!?\n");
	set_fs(old_fs);
	}

	void __init lkdtm_usercopy_init(void)
	{
	/* Prepare cache that lacks SLAB_USERCOPY flag. */
	whitelist_cache =
	kmem_cache_create_usercopy("lkdtm-usercopy", cache_size,
	0, 0,
	cache_size / 4,
	cache_size / 16,
	NULL);
	}

	void __exit lkdtm_usercopy_exit(void)
	{
	kmem_cache_destroy(whitelist_cache);
	}