// SPDX-License-Identifier: GPL-2.0
/*
* Clang Control Flow Integrity (CFI) error and slowpath handling.
*
* Copyright (C) 2021 Google LLC
*/
#include <linux/hardirq.h>
#include <linux/kallsyms.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/printk.h>
#include <linux/ratelimit.h>
#include <linux/rcupdate.h>
#include <linux/vmalloc.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
#else
#define cfi_failure_handler __ubsan_handle_cfi_check_fail_abort
#endif
static inline void handle_cfi_failure(void *ptr)
{
if (IS_ENABLED(CONFIG_CFI_PERMISSIVE))
WARN_RATELIMIT(1, "CFI failure (target: %pS):\n", ptr);
else
panic("CFI failure (target: %pS)\n", ptr);
}
#ifdef CONFIG_MODULES
#ifdef CONFIG_CFI_CLANG_SHADOW
/*
* Index type. A 16-bit index can address at most (2^16)-2 pages (taking
* into account SHADOW_INVALID), i.e. ~256M with 4k pages.
*/
typedef u16 shadow_t;
#define SHADOW_INVALID ((shadow_t)~0UL)
struct cfi_shadow {
/* Page index for the beginning of the shadow */
unsigned long base;
/* An array of __cfi_check locations (as indices to the shadow) */
shadow_t shadow[1];
} __packed;
/*
* The shadow covers ~128M from the beginning of the module region. If
* the region is larger, we fall back to __module_address for the rest.
*/
#define __SHADOW_RANGE (_UL(SZ_128M) >> PAGE_SHIFT)
/* The in-memory size of struct cfi_shadow, always at least one page */
#define __SHADOW_PAGES ((__SHADOW_RANGE * sizeof(shadow_t)) >> PAGE_SHIFT)
#define SHADOW_PAGES max(1UL, __SHADOW_PAGES)
#define SHADOW_SIZE (SHADOW_PAGES << PAGE_SHIFT)
/* The actual size of the shadow array, minus metadata */
#define SHADOW_ARR_SIZE (SHADOW_SIZE - offsetof(struct cfi_shadow, shadow))
#define SHADOW_ARR_SLOTS (SHADOW_ARR_SIZE / sizeof(shadow_t))
static DEFINE_MUTEX(shadow_update_lock);
static struct cfi_shadow __rcu *cfi_shadow __read_mostly;
/* Returns the index in the shadow for the given address */
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->base))
return -1; /* Outside of module area */
index = page - s->base;
if (index >= SHADOW_ARR_SLOTS)
return -1; /* Cannot be addressed with shadow */
return (int)index;
}
/* Returns the page address for an index in the shadow */
static inline unsigned long shadow_to_ptr(const struct cfi_shadow *s,
int index)
{
if (unlikely(index < 0 || index >= SHADOW_ARR_SLOTS))
return 0;
return (s->base + index) << PAGE_SHIFT;
}
/* Returns the __cfi_check function address for the given shadow location */
static inline unsigned long shadow_to_check_fn(const struct cfi_shadow *s,
int index)
{
if (unlikely(index < 0 || index >= SHADOW_ARR_SLOTS))
return 0;
if (unlikely(s->shadow[index] == SHADOW_INVALID))
return 0;
/* __cfi_check is always page aligned */
return (s->base + s->shadow[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, SHADOW_ARR_SIZE);
if (!prev)
return; /* No previous shadow */
/* If the base address didn't change, an update is not needed */
if (prev->base == next->base) {
memcpy(next->shadow, prev->shadow, SHADOW_ARR_SIZE);
return;
}
/* Convert the previous shadow to the new address range */
for (i = 0; i < SHADOW_ARR_SLOTS; ++i) {
if (prev->shadow[i] == SHADOW_INVALID)
continue;
index = ptr_to_shadow(next, shadow_to_ptr(prev, i));
if (index < 0)
continue;
check = ptr_to_shadow(next,
shadow_to_check_fn(prev, prev->shadow[i]));
if (check < 0)
continue;
next->shadow[index] = (shadow_t)check;
}
}
static void add_module_to_shadow(struct cfi_shadow *s, struct module *mod,
unsigned long min_addr, unsigned long max_addr)
{
int check_index;
unsigned long check = (unsigned long)mod->cfi_check;
unsigned long ptr;
if (unlikely(!PAGE_ALIGNED(check))) {
pr_warn("cfi: not using shadow for module %s\n", mod->name);
return;
}
check_index = ptr_to_shadow(s, check);
if (check_index < 0)
return; /* Module not addressable with shadow */
/* For each page, store the check function index in the shadow */
for (ptr = min_addr; ptr <= max_addr; ptr += PAGE_SIZE) {
int index = ptr_to_shadow(s, ptr);
if (index >= 0) {
/* Each page must only contain one module */
WARN_ON_ONCE(s->shadow[index] != SHADOW_INVALID);
s->shadow[index] = (shadow_t)check_index;
}
}
}
static void remove_module_from_shadow(struct cfi_shadow *s, struct module *mod,
unsigned long min_addr, unsigned long max_addr)
{
unsigned long ptr;
for (ptr = min_addr; ptr <= max_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 *,
unsigned long min_addr, unsigned long max_addr);
static void update_shadow(struct module *mod, unsigned long base_addr,
update_shadow_fn fn)
{
struct cfi_shadow *prev;
struct cfi_shadow *next;
unsigned long min_addr, max_addr;
next = vmalloc(SHADOW_SIZE);
mutex_lock(&shadow_update_lock);
prev = rcu_dereference_protected(cfi_shadow,
mutex_is_locked(&shadow_update_lock));
if (next) {
next->base = base_addr >> PAGE_SHIFT;
prepare_next_shadow(prev, next);
min_addr = (unsigned long)mod->core_layout.base;
max_addr = min_addr + mod->core_layout.text_size;
fn(next, mod, min_addr & PAGE_MASK, max_addr & PAGE_MASK);
set_memory_ro((unsigned long)next, SHADOW_PAGES);
}
rcu_assign_pointer(cfi_shadow, next);
mutex_unlock(&shadow_update_lock);
synchronize_rcu();
if (prev) {
set_memory_rw((unsigned long)prev, SHADOW_PAGES);
vfree(prev);
}
}
void cfi_module_add(struct module *mod, unsigned long base_addr)
{
update_shadow(mod, base_addr, add_module_to_shadow);
}
void cfi_module_remove(struct module *mod, unsigned long base_addr)
{
update_shadow(mod, base_addr, remove_module_from_shadow);
}
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 */
index = ptr_to_shadow(s, ptr);
if (index < 0)
return NULL; /* Cannot be addressed with shadow */
return (cfi_check_fn)shadow_to_check_fn(s, index);
}
static inline cfi_check_fn find_shadow_check_fn(unsigned long ptr)
{
cfi_check_fn fn;
rcu_read_lock_sched_notrace();
fn = ptr_to_check_fn(rcu_dereference_sched(cfi_shadow), ptr);
rcu_read_unlock_sched_notrace();
return fn;
}
#else /* !CONFIG_CFI_CLANG_SHADOW */
static inline cfi_check_fn find_shadow_check_fn(unsigned long ptr)
{
return NULL;
}
#endif /* CONFIG_CFI_CLANG_SHADOW */
static inline cfi_check_fn find_module_check_fn(unsigned long ptr)
{
cfi_check_fn fn = NULL;
struct module *mod;
rcu_read_lock_sched_notrace();
mod = __module_address(ptr);
if (mod)
fn = mod->cfi_check;
rcu_read_unlock_sched_notrace();
return fn;
}
static inline cfi_check_fn find_check_fn(unsigned long ptr)
{
cfi_check_fn fn = NULL;
if (is_kernel_text(ptr))
return __cfi_check;
/*
* Indirect call checks can happen when RCU is not watching. Both
* the shadow and __module_address use RCU, so we need to wake it
* up if necessary.
*/
RCU_NONIDLE({
if (IS_ENABLED(CONFIG_CFI_CLANG_SHADOW))
fn = find_shadow_check_fn(ptr);
if (!fn)
fn = find_module_check_fn(ptr);
});
return fn;
}
void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag)
{
cfi_check_fn fn = find_check_fn((unsigned long)ptr);
if (likely(fn))
fn(id, ptr, diag);
else /* Don't allow unchecked modules */
handle_cfi_failure(ptr);
}
EXPORT_SYMBOL(__cfi_slowpath_diag);
#else /* !CONFIG_MODULES */
void __cfi_slowpath_diag(uint64_t id, void *ptr, void *diag)
{
handle_cfi_failure(ptr); /* No modules */
}
EXPORT_SYMBOL(__cfi_slowpath_diag);
#endif /* CONFIG_MODULES */
void cfi_failure_handler(void *data, void *ptr, void *vtable)
{
handle_cfi_failure(ptr);
}
EXPORT_SYMBOL(cfi_failure_handler);
