blob: b23f6ede42ca6e2bb9488cd1b3adeec2eb420586 [file] [log] [blame]
/*
* 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: [<%px>] %pF):\n", ptr, ptr);
#else
pr_err("CFI failure (target: [<%px>] %pF):\n", ptr, 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);
}