kernel/cfi.c - kernel/common.git - Git at Google

 /*
  * CFI (Control Flow Integrity) error and slowpath handling
  *
  * Copyright (C) 2017 Google, Inc.
  */

 #include <linux/gfp.h>
 #include <linux/module.h>
 #include <linux/printk.h>
 #include <linux/ratelimit.h>
 #include <linux/rcupdate.h>
 #include <linux/spinlock.h>
 #include <asm/bug.h>
 #include <asm/cacheflush.h>
 #include <asm/set_memory.h>

 /* Compiler-defined handler names */
 #ifdef CONFIG_CFI_PERMISSIVE
 #define cfi_failure_handler	__ubsan_handle_cfi_check_fail
 #define cfi_slowpath_handler	__cfi_slowpath_diag
 #else /* enforcing */
 #define cfi_failure_handler	__ubsan_handle_cfi_check_fail_abort
 #define cfi_slowpath_handler	__cfi_slowpath
 #endif /* CONFIG_CFI_PERMISSIVE */

 static inline void handle_cfi_failure(void *ptr)
 {
 #ifdef CONFIG_CFI_PERMISSIVE
 	WARN_RATELIMIT(1, "CFI failure (target: %pF):\n", ptr);
 #else
 	pr_err("CFI failure (target: %pF):\n", ptr);
 	BUG();
 #endif
 }

 #ifdef CONFIG_MODULES
 #ifdef CONFIG_CFI_CLANG_SHADOW
 struct shadow_range {
 	/* Module address range */
 	unsigned long mod_min_addr;
 	unsigned long mod_max_addr;
 	/* Module page range */
 	unsigned long min_page;
 	unsigned long max_page;
 };

 #define SHADOW_ORDER	1
 #define SHADOW_PAGES	(1 << SHADOW_ORDER)
 #define SHADOW_SIZE \
 	((SHADOW_PAGES * PAGE_SIZE - sizeof(struct shadow_range)) / sizeof(u16))
 #define SHADOW_INVALID	0xFFFF

 struct cfi_shadow {
 	/* Page range covered by the shadow */
 	struct shadow_range r;
 	/* Page offsets to __cfi_check functions in modules */
 	u16 shadow[SHADOW_SIZE];
 };

 static DEFINE_SPINLOCK(shadow_update_lock);
 static struct cfi_shadow __rcu *cfi_shadow __read_mostly = NULL;

 static inline int ptr_to_shadow(const struct cfi_shadow *s, unsigned long ptr)
 {
 	unsigned long index;
 	unsigned long page = ptr >> PAGE_SHIFT;

 	if (unlikely(page < s->r.min_page))
 		return -1; /* Outside of module area */

 	index = page - s->r.min_page;

 	if (index >= SHADOW_SIZE)
 		return -1; /* Cannot be addressed with shadow */

 	return (int)index;
 }

 static inline unsigned long shadow_to_ptr(const struct cfi_shadow *s,
 	int index)
 {
 	BUG_ON(index < 0 || index >= SHADOW_SIZE);

 	if (unlikely(s->shadow[index] == SHADOW_INVALID))
 		return 0;

 	return (s->r.min_page + s->shadow[index]) << PAGE_SHIFT;
 }

 static inline unsigned long shadow_to_page(const struct cfi_shadow *s,
 	int index)
 {
 	BUG_ON(index < 0 || index >= SHADOW_SIZE);

 	return (s->r.min_page + index) << PAGE_SHIFT;
 }

 static void prepare_next_shadow(const struct cfi_shadow __rcu *prev,
 		struct cfi_shadow *next)
 {
 	int i, index, check;

 	/* Mark everything invalid */
 	memset(next->shadow, 0xFF, sizeof(next->shadow));

 	if (!prev)
 		return; /* No previous shadow */

 	/* If the base address didn't change, update is not needed */
 	if (prev->r.min_page == next->r.min_page) {
 		memcpy(next->shadow, prev->shadow, sizeof(next->shadow));
 		return;
 	}

 	/* Convert the previous shadow to the new address range */
 	for (i = 0; i < SHADOW_SIZE; ++i) {
 		if (prev->shadow[i] == SHADOW_INVALID)
 			continue;

 		index = ptr_to_shadow(next, shadow_to_page(prev, i));
 		if (index < 0)
 			continue;

 		check = ptr_to_shadow(next,
 				shadow_to_ptr(prev, prev->shadow[i]));
 		if (check < 0)
 			continue;

 		next->shadow[index] = (u16)check;
 	}
 }

 static void add_module_to_shadow(struct cfi_shadow *s, struct module *mod)
 {
 	unsigned long ptr;
 	unsigned long min_page_addr;
 	unsigned long max_page_addr;
 	unsigned long check = (unsigned long)mod->cfi_check;
 	int check_index = ptr_to_shadow(s, check);

 	BUG_ON((check & PAGE_MASK) != check); /* Must be page aligned */

 	if (check_index < 0)
 		return; /* Module not addressable with shadow */

 	min_page_addr = (unsigned long)mod->core_layout.base & PAGE_MASK;
 	max_page_addr = (unsigned long)mod->core_layout.base +
 				       mod->core_layout.text_size;
 	max_page_addr &= PAGE_MASK;

 	/* For each page, store the check function index in the shadow */
 	for (ptr = min_page_addr; ptr <= max_page_addr; ptr += PAGE_SIZE) {
 		int index = ptr_to_shadow(s, ptr);
 		if (index >= 0) {
 			/* Assume a page only contains code for one module */
 			BUG_ON(s->shadow[index] != SHADOW_INVALID);
 			s->shadow[index] = (u16)check_index;
 		}
 	}
 }

 static void remove_module_from_shadow(struct cfi_shadow *s, struct module *mod)
 {
 	unsigned long ptr;
 	unsigned long min_page_addr;
 	unsigned long max_page_addr;

 	min_page_addr = (unsigned long)mod->core_layout.base & PAGE_MASK;
 	max_page_addr = (unsigned long)mod->core_layout.base +
 				       mod->core_layout.text_size;
 	max_page_addr &= PAGE_MASK;

 	for (ptr = min_page_addr; ptr <= max_page_addr; ptr += PAGE_SIZE) {
 		int index = ptr_to_shadow(s, ptr);
 		if (index >= 0)
 			s->shadow[index] = SHADOW_INVALID;
 	}
 }

 typedef void (*update_shadow_fn)(struct cfi_shadow *, struct module *);

 static void update_shadow(struct module *mod, unsigned long min_addr,
 	unsigned long max_addr, update_shadow_fn fn)
 {
 	struct cfi_shadow *prev;
 	struct cfi_shadow *next = (struct cfi_shadow *)
 		__get_free_pages(GFP_KERNEL, SHADOW_ORDER);

 	BUG_ON(!next);

 	next->r.mod_min_addr = min_addr;
 	next->r.mod_max_addr = max_addr;
 	next->r.min_page = min_addr >> PAGE_SHIFT;
 	next->r.max_page = max_addr >> PAGE_SHIFT;

 	spin_lock(&shadow_update_lock);
 	prev = rcu_dereference_protected(cfi_shadow, 1);
 	prepare_next_shadow(prev, next);

 	fn(next, mod);
 	set_memory_ro((unsigned long)next, SHADOW_PAGES);
 	rcu_assign_pointer(cfi_shadow, next);

 	spin_unlock(&shadow_update_lock);
 	synchronize_rcu();

 	if (prev) {
 		set_memory_rw((unsigned long)prev, SHADOW_PAGES);
 		free_pages((unsigned long)prev, SHADOW_ORDER);
 	}
 }

 void cfi_module_add(struct module *mod, unsigned long min_addr,
 	unsigned long max_addr)
 {
 	update_shadow(mod, min_addr, max_addr, add_module_to_shadow);
 }
 EXPORT_SYMBOL(cfi_module_add);

 void cfi_module_remove(struct module *mod, unsigned long min_addr,
 	unsigned long max_addr)
 {
 	update_shadow(mod, min_addr, max_addr, remove_module_from_shadow);
 }
 EXPORT_SYMBOL(cfi_module_remove);

 static inline cfi_check_fn ptr_to_check_fn(const struct cfi_shadow __rcu *s,
 	unsigned long ptr)
 {
 	int index;

 	if (unlikely(!s))
 		return NULL; /* No shadow available */

 	if (ptr < s->r.mod_min_addr || ptr > s->r.mod_max_addr)
 		return NULL; /* Not in a mapped module */

 	index = ptr_to_shadow(s, ptr);
 	if (index < 0)
 		return NULL; /* Cannot be addressed with shadow */

 	return (cfi_check_fn)shadow_to_ptr(s, index);
 }
 #endif /* CONFIG_CFI_CLANG_SHADOW */

 static inline cfi_check_fn find_module_cfi_check(void *ptr)
 {
 	struct module *mod;

 	preempt_disable();
 	mod = __module_address((unsigned long)ptr);
 	preempt_enable();

 	if (mod)
 		return mod->cfi_check;

 	return CFI_CHECK_FN;
 }

 static inline cfi_check_fn find_cfi_check(void *ptr)
 {
 #ifdef CONFIG_CFI_CLANG_SHADOW
 	cfi_check_fn f;

 	if (!rcu_access_pointer(cfi_shadow))
 		return CFI_CHECK_FN; /* No loaded modules */

 	/* Look up the __cfi_check function to use */
 	rcu_read_lock();
 	f = ptr_to_check_fn(rcu_dereference(cfi_shadow), (unsigned long)ptr);
 	rcu_read_unlock();

 	if (f)
 		return f;

 	/*
 	 * Fall back to find_module_cfi_check, which works also for a larger
 	 * module address space, but is slower.
 	 */
 #endif /* CONFIG_CFI_CLANG_SHADOW */

 	return find_module_cfi_check(ptr);
 }

 void cfi_slowpath_handler(uint64_t id, void *ptr, void *diag)
 {
 	cfi_check_fn check = find_cfi_check(ptr);

 	if (likely(check))
 		check(id, ptr, diag);
 	else /* Don't allow unchecked modules */
 		handle_cfi_failure(ptr);
 }
 EXPORT_SYMBOL(cfi_slowpath_handler);
 #endif /* CONFIG_MODULES */

 void cfi_failure_handler(void *data, void *ptr, void *vtable)
 {
 	handle_cfi_failure(ptr);
 }
 EXPORT_SYMBOL(cfi_failure_handler);

 void __cfi_check_fail(void *data, void *ptr)
 {
 	handle_cfi_failure(ptr);
 }
	/*
	* CFI (Control Flow Integrity) error and slowpath handling
	*
	* Copyright (C) 2017 Google, Inc.
	*/

	#include <linux/gfp.h>
	#include <linux/module.h>
	#include <linux/printk.h>
	#include <linux/ratelimit.h>
	#include <linux/rcupdate.h>
	#include <linux/spinlock.h>
	#include <asm/bug.h>
	#include <asm/cacheflush.h>
	#include <asm/set_memory.h>

	/* Compiler-defined handler names */
	#ifdef CONFIG_CFI_PERMISSIVE
	#define cfi_failure_handler __ubsan_handle_cfi_check_fail
	#define cfi_slowpath_handler __cfi_slowpath_diag
	#else /* enforcing */
	#define cfi_failure_handler __ubsan_handle_cfi_check_fail_abort
	#define cfi_slowpath_handler __cfi_slowpath
	#endif /* CONFIG_CFI_PERMISSIVE */

	static inline void handle_cfi_failure(void *ptr)
	{
	#ifdef CONFIG_CFI_PERMISSIVE
	WARN_RATELIMIT(1, "CFI failure (target: %pF):\n", ptr);
	#else
	pr_err("CFI failure (target: %pF):\n", ptr);
	BUG();
	#endif
	}

	#ifdef CONFIG_MODULES
	#ifdef CONFIG_CFI_CLANG_SHADOW
	struct shadow_range {
	/* Module address range */
	unsigned long mod_min_addr;
	unsigned long mod_max_addr;
	/* Module page range */
	unsigned long min_page;
	unsigned long max_page;
	};

	#define SHADOW_ORDER 1
	#define SHADOW_PAGES (1 << SHADOW_ORDER)
	#define SHADOW_SIZE \
	((SHADOW_PAGES * PAGE_SIZE - sizeof(struct shadow_range)) / sizeof(u16))
	#define SHADOW_INVALID 0xFFFF

	struct cfi_shadow {
	/* Page range covered by the shadow */
	struct shadow_range r;
	/* Page offsets to __cfi_check functions in modules */
	u16 shadow[SHADOW_SIZE];
	};

	static DEFINE_SPINLOCK(shadow_update_lock);
	static struct cfi_shadow __rcu *cfi_shadow __read_mostly = NULL;

	static inline int ptr_to_shadow(const struct cfi_shadow *s, unsigned long ptr)
	{
	unsigned long index;
	unsigned long page = ptr >> PAGE_SHIFT;

	if (unlikely(page < s->r.min_page))
	return -1; /* Outside of module area */

	index = page - s->r.min_page;

	if (index >= SHADOW_SIZE)
	return -1; /* Cannot be addressed with shadow */

	return (int)index;
	}

	static inline unsigned long shadow_to_ptr(const struct cfi_shadow *s,
	int index)
	{
	BUG_ON(index < 0 \|\| index >= SHADOW_SIZE);

	if (unlikely(s->shadow[index] == SHADOW_INVALID))
	return 0;

	return (s->r.min_page + s->shadow[index]) << PAGE_SHIFT;
	}

	static inline unsigned long shadow_to_page(const struct cfi_shadow *s,
	int index)
	{
	BUG_ON(index < 0 \|\| index >= SHADOW_SIZE);

	return (s->r.min_page + index) << PAGE_SHIFT;
	}

	static void prepare_next_shadow(const struct cfi_shadow __rcu *prev,
	struct cfi_shadow *next)
	{
	int i, index, check;

	/* Mark everything invalid */
	memset(next->shadow, 0xFF, sizeof(next->shadow));

	if (!prev)
	return; /* No previous shadow */

	/* If the base address didn't change, update is not needed */
	if (prev->r.min_page == next->r.min_page) {
	memcpy(next->shadow, prev->shadow, sizeof(next->shadow));
	return;
	}

	/* Convert the previous shadow to the new address range */
	for (i = 0; i < SHADOW_SIZE; ++i) {
	if (prev->shadow[i] == SHADOW_INVALID)
	continue;

	index = ptr_to_shadow(next, shadow_to_page(prev, i));
	if (index < 0)
	continue;

	check = ptr_to_shadow(next,
	shadow_to_ptr(prev, prev->shadow[i]));
	if (check < 0)
	continue;

	next->shadow[index] = (u16)check;
	}
	}

	static void add_module_to_shadow(struct cfi_shadow s, struct module mod)
	{
	unsigned long ptr;
	unsigned long min_page_addr;
	unsigned long max_page_addr;
	unsigned long check = (unsigned long)mod->cfi_check;
	int check_index = ptr_to_shadow(s, check);

	BUG_ON((check & PAGE_MASK) != check); /* Must be page aligned */

	if (check_index < 0)
	return; /* Module not addressable with shadow */

	min_page_addr = (unsigned long)mod->core_layout.base & PAGE_MASK;
	max_page_addr = (unsigned long)mod->core_layout.base +
	mod->core_layout.text_size;
	max_page_addr &= PAGE_MASK;

	/* For each page, store the check function index in the shadow */
	for (ptr = min_page_addr; ptr <= max_page_addr; ptr += PAGE_SIZE) {
	int index = ptr_to_shadow(s, ptr);
	if (index >= 0) {
	/* Assume a page only contains code for one module */
	BUG_ON(s->shadow[index] != SHADOW_INVALID);
	s->shadow[index] = (u16)check_index;
	}
	}
	}

	static void remove_module_from_shadow(struct cfi_shadow s, struct module mod)
	{
	unsigned long ptr;
	unsigned long min_page_addr;
	unsigned long max_page_addr;

	min_page_addr = (unsigned long)mod->core_layout.base & PAGE_MASK;
	max_page_addr = (unsigned long)mod->core_layout.base +
	mod->core_layout.text_size;
	max_page_addr &= PAGE_MASK;

	for (ptr = min_page_addr; ptr <= max_page_addr; ptr += PAGE_SIZE) {
	int index = ptr_to_shadow(s, ptr);
	if (index >= 0)
	s->shadow[index] = SHADOW_INVALID;
	}
	}

	typedef void (update_shadow_fn)(struct cfi_shadow , struct module *);

	static void update_shadow(struct module *mod, unsigned long min_addr,
	unsigned long max_addr, update_shadow_fn fn)
	{
	struct cfi_shadow *prev;
	struct cfi_shadow next = (struct cfi_shadow )
	__get_free_pages(GFP_KERNEL, SHADOW_ORDER);

	BUG_ON(!next);

	next->r.mod_min_addr = min_addr;
	next->r.mod_max_addr = max_addr;
	next->r.min_page = min_addr >> PAGE_SHIFT;
	next->r.max_page = max_addr >> PAGE_SHIFT;

	spin_lock(&shadow_update_lock);
	prev = rcu_dereference_protected(cfi_shadow, 1);
	prepare_next_shadow(prev, next);

	fn(next, mod);
	set_memory_ro((unsigned long)next, SHADOW_PAGES);
	rcu_assign_pointer(cfi_shadow, next);

	spin_unlock(&shadow_update_lock);
	synchronize_rcu();

	if (prev) {
	set_memory_rw((unsigned long)prev, SHADOW_PAGES);
	free_pages((unsigned long)prev, SHADOW_ORDER);
	}
	}

	void cfi_module_add(struct module *mod, unsigned long min_addr,
	unsigned long max_addr)
	{
	update_shadow(mod, min_addr, max_addr, add_module_to_shadow);
	}
	EXPORT_SYMBOL(cfi_module_add);

	void cfi_module_remove(struct module *mod, unsigned long min_addr,
	unsigned long max_addr)
	{
	update_shadow(mod, min_addr, max_addr, remove_module_from_shadow);
	}
	EXPORT_SYMBOL(cfi_module_remove);

	static inline cfi_check_fn ptr_to_check_fn(const struct cfi_shadow __rcu *s,
	unsigned long ptr)
	{
	int index;

	if (unlikely(!s))
	return NULL; /* No shadow available */

	if (ptr < s->r.mod_min_addr \|\| ptr > s->r.mod_max_addr)
	return NULL; /* Not in a mapped module */

	index = ptr_to_shadow(s, ptr);
	if (index < 0)
	return NULL; /* Cannot be addressed with shadow */

	return (cfi_check_fn)shadow_to_ptr(s, index);
	}
	#endif /* CONFIG_CFI_CLANG_SHADOW */

	static inline cfi_check_fn find_module_cfi_check(void *ptr)
	{
	struct module *mod;

	preempt_disable();
	mod = __module_address((unsigned long)ptr);
	preempt_enable();

	if (mod)
	return mod->cfi_check;

	return CFI_CHECK_FN;
	}

	static inline cfi_check_fn find_cfi_check(void *ptr)
	{
	#ifdef CONFIG_CFI_CLANG_SHADOW
	cfi_check_fn f;

	if (!rcu_access_pointer(cfi_shadow))
	return CFI_CHECK_FN; /* No loaded modules */

	/* Look up the __cfi_check function to use */
	rcu_read_lock();
	f = ptr_to_check_fn(rcu_dereference(cfi_shadow), (unsigned long)ptr);
	rcu_read_unlock();

	if (f)
	return f;

	/*
	* Fall back to find_module_cfi_check, which works also for a larger
	* module address space, but is slower.
	*/
	#endif /* CONFIG_CFI_CLANG_SHADOW */

	return find_module_cfi_check(ptr);
	}

	void cfi_slowpath_handler(uint64_t id, void ptr, void diag)
	{
	cfi_check_fn check = find_cfi_check(ptr);

	if (likely(check))
	check(id, ptr, diag);
	else /* Don't allow unchecked modules */
	handle_cfi_failure(ptr);
	}
	EXPORT_SYMBOL(cfi_slowpath_handler);
	#endif /* CONFIG_MODULES */

	void cfi_failure_handler(void data, void ptr, void *vtable)
	{
	handle_cfi_failure(ptr);
	}
	EXPORT_SYMBOL(cfi_failure_handler);

	void __cfi_check_fail(void data, void ptr)
	{
	handle_cfi_failure(ptr);
	}