1 // SPDX-License-Identifier: GPL-2.0
3 * KFENCE guarded object allocator and fault handling.
5 * Copyright (C) 2020, Google LLC.
8 #define pr_fmt(fmt) "kfence: " fmt
10 #include <linux/atomic.h>
11 #include <linux/bug.h>
12 #include <linux/debugfs.h>
13 #include <linux/kcsan-checks.h>
14 #include <linux/kfence.h>
15 #include <linux/kmemleak.h>
16 #include <linux/list.h>
17 #include <linux/lockdep.h>
18 #include <linux/memblock.h>
19 #include <linux/moduleparam.h>
20 #include <linux/random.h>
21 #include <linux/rcupdate.h>
22 #include <linux/seq_file.h>
23 #include <linux/slab.h>
24 #include <linux/spinlock.h>
25 #include <linux/string.h>
27 #include <asm/kfence.h>
31 /* Disables KFENCE on the first warning assuming an irrecoverable error. */
32 #define KFENCE_WARN_ON(cond) \
34 const bool __cond = WARN_ON(cond); \
35 if (unlikely(__cond)) \
36 WRITE_ONCE(kfence_enabled, false); \
40 /* === Data ================================================================= */
42 static bool kfence_enabled __read_mostly;
44 static unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL;
46 #ifdef MODULE_PARAM_PREFIX
47 #undef MODULE_PARAM_PREFIX
49 #define MODULE_PARAM_PREFIX "kfence."
51 static int param_set_sample_interval(const char *val, const struct kernel_param *kp)
54 int ret = kstrtoul(val, 0, &num);
59 if (!num) /* Using 0 to indicate KFENCE is disabled. */
60 WRITE_ONCE(kfence_enabled, false);
61 else if (!READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING)
62 return -EINVAL; /* Cannot (re-)enable KFENCE on-the-fly. */
64 *((unsigned long *)kp->arg) = num;
68 static int param_get_sample_interval(char *buffer, const struct kernel_param *kp)
70 if (!READ_ONCE(kfence_enabled))
71 return sprintf(buffer, "0\n");
73 return param_get_ulong(buffer, kp);
76 static const struct kernel_param_ops sample_interval_param_ops = {
77 .set = param_set_sample_interval,
78 .get = param_get_sample_interval,
80 module_param_cb(sample_interval, &sample_interval_param_ops, &kfence_sample_interval, 0600);
82 /* The pool of pages used for guard pages and objects. */
83 char *__kfence_pool __ro_after_init;
84 EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */
87 * Per-object metadata, with one-to-one mapping of object metadata to
88 * backing pages (in __kfence_pool).
90 static_assert(CONFIG_KFENCE_NUM_OBJECTS > 0);
91 struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
93 /* Freelist with available objects. */
94 static struct list_head kfence_freelist = LIST_HEAD_INIT(kfence_freelist);
95 static DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */
97 #ifdef CONFIG_KFENCE_STATIC_KEYS
98 /* The static key to set up a KFENCE allocation. */
99 DEFINE_STATIC_KEY_FALSE(kfence_allocation_key);
102 /* Gates the allocation, ensuring only one succeeds in a given period. */
103 atomic_t kfence_allocation_gate = ATOMIC_INIT(1);
105 /* Statistics counters for debugfs. */
106 enum kfence_counter_id {
107 KFENCE_COUNTER_ALLOCATED,
108 KFENCE_COUNTER_ALLOCS,
109 KFENCE_COUNTER_FREES,
110 KFENCE_COUNTER_ZOMBIES,
112 KFENCE_COUNTER_COUNT,
114 static atomic_long_t counters[KFENCE_COUNTER_COUNT];
115 static const char *const counter_names[] = {
116 [KFENCE_COUNTER_ALLOCATED] = "currently allocated",
117 [KFENCE_COUNTER_ALLOCS] = "total allocations",
118 [KFENCE_COUNTER_FREES] = "total frees",
119 [KFENCE_COUNTER_ZOMBIES] = "zombie allocations",
120 [KFENCE_COUNTER_BUGS] = "total bugs",
122 static_assert(ARRAY_SIZE(counter_names) == KFENCE_COUNTER_COUNT);
124 /* === Internals ============================================================ */
126 static bool kfence_protect(unsigned long addr)
128 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), true));
131 static bool kfence_unprotect(unsigned long addr)
133 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), false));
136 static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
140 /* The checks do not affect performance; only called from slow-paths. */
142 if (!is_kfence_address((void *)addr))
146 * May be an invalid index if called with an address at the edge of
147 * __kfence_pool, in which case we would report an "invalid access"
150 index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
151 if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS)
154 return &kfence_metadata[index];
157 static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta)
159 unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2;
160 unsigned long pageaddr = (unsigned long)&__kfence_pool[offset];
162 /* The checks do not affect performance; only called from slow-paths. */
164 /* Only call with a pointer into kfence_metadata. */
165 if (KFENCE_WARN_ON(meta < kfence_metadata ||
166 meta >= kfence_metadata + CONFIG_KFENCE_NUM_OBJECTS))
170 * This metadata object only ever maps to 1 page; verify that the stored
171 * address is in the expected range.
173 if (KFENCE_WARN_ON(ALIGN_DOWN(meta->addr, PAGE_SIZE) != pageaddr))
180 * Update the object's metadata state, including updating the alloc/free stacks
181 * depending on the state transition.
183 static noinline void metadata_update_state(struct kfence_metadata *meta,
184 enum kfence_object_state next)
186 struct kfence_track *track =
187 next == KFENCE_OBJECT_FREED ? &meta->free_track : &meta->alloc_track;
189 lockdep_assert_held(&meta->lock);
192 * Skip over 1 (this) functions; noinline ensures we do not accidentally
193 * skip over the caller by never inlining.
195 track->num_stack_entries = stack_trace_save(track->stack_entries, KFENCE_STACK_DEPTH, 1);
196 track->pid = task_pid_nr(current);
199 * Pairs with READ_ONCE() in
200 * kfence_shutdown_cache(),
201 * kfence_handle_page_fault().
203 WRITE_ONCE(meta->state, next);
206 /* Write canary byte to @addr. */
207 static inline bool set_canary_byte(u8 *addr)
209 *addr = KFENCE_CANARY_PATTERN(addr);
213 /* Check canary byte at @addr. */
214 static inline bool check_canary_byte(u8 *addr)
216 if (likely(*addr == KFENCE_CANARY_PATTERN(addr)))
219 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
220 kfence_report_error((unsigned long)addr, false, NULL, addr_to_metadata((unsigned long)addr),
221 KFENCE_ERROR_CORRUPTION);
225 /* __always_inline this to ensure we won't do an indirect call to fn. */
226 static __always_inline void for_each_canary(const struct kfence_metadata *meta, bool (*fn)(u8 *))
228 const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE);
231 lockdep_assert_held(&meta->lock);
234 * We'll iterate over each canary byte per-side until fn() returns
235 * false. However, we'll still iterate over the canary bytes to the
236 * right of the object even if there was an error in the canary bytes to
237 * the left of the object. Specifically, if check_canary_byte()
238 * generates an error, showing both sides might give more clues as to
239 * what the error is about when displaying which bytes were corrupted.
242 /* Apply to left of object. */
243 for (addr = pageaddr; addr < meta->addr; addr++) {
248 /* Apply to right of object. */
249 for (addr = meta->addr + meta->size; addr < pageaddr + PAGE_SIZE; addr++) {
255 static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t gfp)
257 struct kfence_metadata *meta = NULL;
262 /* Try to obtain a free object. */
263 raw_spin_lock_irqsave(&kfence_freelist_lock, flags);
264 if (!list_empty(&kfence_freelist)) {
265 meta = list_entry(kfence_freelist.next, struct kfence_metadata, list);
266 list_del_init(&meta->list);
268 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);
272 if (unlikely(!raw_spin_trylock_irqsave(&meta->lock, flags))) {
274 * This is extremely unlikely -- we are reporting on a
275 * use-after-free, which locked meta->lock, and the reporting
276 * code via printk calls kmalloc() which ends up in
277 * kfence_alloc() and tries to grab the same object that we're
278 * reporting on. While it has never been observed, lockdep does
279 * report that there is a possibility of deadlock. Fix it by
280 * using trylock and bailing out gracefully.
282 raw_spin_lock_irqsave(&kfence_freelist_lock, flags);
283 /* Put the object back on the freelist. */
284 list_add_tail(&meta->list, &kfence_freelist);
285 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);
290 meta->addr = metadata_to_pageaddr(meta);
291 /* Unprotect if we're reusing this page. */
292 if (meta->state == KFENCE_OBJECT_FREED)
293 kfence_unprotect(meta->addr);
296 * Note: for allocations made before RNG initialization, will always
297 * return zero. We still benefit from enabling KFENCE as early as
298 * possible, even when the RNG is not yet available, as this will allow
299 * KFENCE to detect bugs due to earlier allocations. The only downside
300 * is that the out-of-bounds accesses detected are deterministic for
303 if (prandom_u32_max(2)) {
304 /* Allocate on the "right" side, re-calculate address. */
305 meta->addr += PAGE_SIZE - size;
306 meta->addr = ALIGN_DOWN(meta->addr, cache->align);
309 addr = (void *)meta->addr;
311 /* Update remaining metadata. */
312 metadata_update_state(meta, KFENCE_OBJECT_ALLOCATED);
313 /* Pairs with READ_ONCE() in kfence_shutdown_cache(). */
314 WRITE_ONCE(meta->cache, cache);
316 for_each_canary(meta, set_canary_byte);
318 /* Set required struct page fields. */
319 page = virt_to_page(meta->addr);
320 page->slab_cache = cache;
321 if (IS_ENABLED(CONFIG_SLUB))
323 if (IS_ENABLED(CONFIG_SLAB))
326 raw_spin_unlock_irqrestore(&meta->lock, flags);
328 /* Memory initialization. */
331 * We check slab_want_init_on_alloc() ourselves, rather than letting
332 * SL*B do the initialization, as otherwise we might overwrite KFENCE's
335 if (unlikely(slab_want_init_on_alloc(gfp, cache)))
336 memzero_explicit(addr, size);
340 if (CONFIG_KFENCE_STRESS_TEST_FAULTS && !prandom_u32_max(CONFIG_KFENCE_STRESS_TEST_FAULTS))
341 kfence_protect(meta->addr); /* Random "faults" by protecting the object. */
343 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCATED]);
344 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCS]);
349 static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool zombie)
351 struct kcsan_scoped_access assert_page_exclusive;
354 raw_spin_lock_irqsave(&meta->lock, flags);
356 if (meta->state != KFENCE_OBJECT_ALLOCATED || meta->addr != (unsigned long)addr) {
357 /* Invalid or double-free, bail out. */
358 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
359 kfence_report_error((unsigned long)addr, false, NULL, meta,
360 KFENCE_ERROR_INVALID_FREE);
361 raw_spin_unlock_irqrestore(&meta->lock, flags);
365 /* Detect racy use-after-free, or incorrect reallocation of this page by KFENCE. */
366 kcsan_begin_scoped_access((void *)ALIGN_DOWN((unsigned long)addr, PAGE_SIZE), PAGE_SIZE,
367 KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT,
368 &assert_page_exclusive);
370 if (CONFIG_KFENCE_STRESS_TEST_FAULTS)
371 kfence_unprotect((unsigned long)addr); /* To check canary bytes. */
373 /* Restore page protection if there was an OOB access. */
374 if (meta->unprotected_page) {
375 kfence_protect(meta->unprotected_page);
376 meta->unprotected_page = 0;
379 /* Check canary bytes for memory corruption. */
380 for_each_canary(meta, check_canary_byte);
383 * Clear memory if init-on-free is set. While we protect the page, the
384 * data is still there, and after a use-after-free is detected, we
385 * unprotect the page, so the data is still accessible.
387 if (!zombie && unlikely(slab_want_init_on_free(meta->cache)))
388 memzero_explicit(addr, meta->size);
390 /* Mark the object as freed. */
391 metadata_update_state(meta, KFENCE_OBJECT_FREED);
393 raw_spin_unlock_irqrestore(&meta->lock, flags);
395 /* Protect to detect use-after-frees. */
396 kfence_protect((unsigned long)addr);
398 kcsan_end_scoped_access(&assert_page_exclusive);
400 /* Add it to the tail of the freelist for reuse. */
401 raw_spin_lock_irqsave(&kfence_freelist_lock, flags);
402 KFENCE_WARN_ON(!list_empty(&meta->list));
403 list_add_tail(&meta->list, &kfence_freelist);
404 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);
406 atomic_long_dec(&counters[KFENCE_COUNTER_ALLOCATED]);
407 atomic_long_inc(&counters[KFENCE_COUNTER_FREES]);
409 /* See kfence_shutdown_cache(). */
410 atomic_long_inc(&counters[KFENCE_COUNTER_ZOMBIES]);
414 static void rcu_guarded_free(struct rcu_head *h)
416 struct kfence_metadata *meta = container_of(h, struct kfence_metadata, rcu_head);
418 kfence_guarded_free((void *)meta->addr, meta, false);
421 static bool __init kfence_init_pool(void)
423 unsigned long addr = (unsigned long)__kfence_pool;
430 if (!arch_kfence_init_pool())
433 pages = virt_to_page(addr);
436 * Set up object pages: they must have PG_slab set, to avoid freeing
437 * these as real pages.
439 * We also want to avoid inserting kfence_free() in the kfree()
440 * fast-path in SLUB, and therefore need to ensure kfree() correctly
441 * enters __slab_free() slow-path.
443 for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
447 /* Verify we do not have a compound head page. */
448 if (WARN_ON(compound_head(&pages[i]) != &pages[i]))
451 __SetPageSlab(&pages[i]);
455 * Protect the first 2 pages. The first page is mostly unnecessary, and
456 * merely serves as an extended guard page. However, adding one
457 * additional page in the beginning gives us an even number of pages,
458 * which simplifies the mapping of address to metadata index.
460 for (i = 0; i < 2; i++) {
461 if (unlikely(!kfence_protect(addr)))
467 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
468 struct kfence_metadata *meta = &kfence_metadata[i];
470 /* Initialize metadata. */
471 INIT_LIST_HEAD(&meta->list);
472 raw_spin_lock_init(&meta->lock);
473 meta->state = KFENCE_OBJECT_UNUSED;
474 meta->addr = addr; /* Initialize for validation in metadata_to_pageaddr(). */
475 list_add_tail(&meta->list, &kfence_freelist);
477 /* Protect the right redzone. */
478 if (unlikely(!kfence_protect(addr + PAGE_SIZE)))
481 addr += 2 * PAGE_SIZE;
485 * The pool is live and will never be deallocated from this point on.
486 * Remove the pool object from the kmemleak object tree, as it would
487 * otherwise overlap with allocations returned by kfence_alloc(), which
488 * are registered with kmemleak through the slab post-alloc hook.
490 kmemleak_free(__kfence_pool);
496 * Only release unprotected pages, and do not try to go back and change
497 * page attributes due to risk of failing to do so as well. If changing
498 * page attributes for some pages fails, it is very likely that it also
499 * fails for the first page, and therefore expect addr==__kfence_pool in
500 * most failure cases.
502 memblock_free_late(__pa(addr), KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool));
503 __kfence_pool = NULL;
507 /* === DebugFS Interface ==================================================== */
509 static int stats_show(struct seq_file *seq, void *v)
513 seq_printf(seq, "enabled: %i\n", READ_ONCE(kfence_enabled));
514 for (i = 0; i < KFENCE_COUNTER_COUNT; i++)
515 seq_printf(seq, "%s: %ld\n", counter_names[i], atomic_long_read(&counters[i]));
519 DEFINE_SHOW_ATTRIBUTE(stats);
522 * debugfs seq_file operations for /sys/kernel/debug/kfence/objects.
523 * start_object() and next_object() return the object index + 1, because NULL is used
526 static void *start_object(struct seq_file *seq, loff_t *pos)
528 if (*pos < CONFIG_KFENCE_NUM_OBJECTS)
529 return (void *)((long)*pos + 1);
533 static void stop_object(struct seq_file *seq, void *v)
537 static void *next_object(struct seq_file *seq, void *v, loff_t *pos)
540 if (*pos < CONFIG_KFENCE_NUM_OBJECTS)
541 return (void *)((long)*pos + 1);
545 static int show_object(struct seq_file *seq, void *v)
547 struct kfence_metadata *meta = &kfence_metadata[(long)v - 1];
550 raw_spin_lock_irqsave(&meta->lock, flags);
551 kfence_print_object(seq, meta);
552 raw_spin_unlock_irqrestore(&meta->lock, flags);
553 seq_puts(seq, "---------------------------------\n");
558 static const struct seq_operations object_seqops = {
559 .start = start_object,
565 static int open_objects(struct inode *inode, struct file *file)
567 return seq_open(file, &object_seqops);
570 static const struct file_operations objects_fops = {
571 .open = open_objects,
576 static int __init kfence_debugfs_init(void)
578 struct dentry *kfence_dir = debugfs_create_dir("kfence", NULL);
580 debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops);
581 debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops);
585 late_initcall(kfence_debugfs_init);
587 /* === Allocation Gate Timer ================================================ */
590 * Set up delayed work, which will enable and disable the static key. We need to
591 * use a work queue (rather than a simple timer), since enabling and disabling a
592 * static key cannot be done from an interrupt.
594 * Note: Toggling a static branch currently causes IPIs, and here we'll end up
595 * with a total of 2 IPIs to all CPUs. If this ends up a problem in future (with
596 * more aggressive sampling intervals), we could get away with a variant that
597 * avoids IPIs, at the cost of not immediately capturing allocations if the
598 * instructions remain cached.
600 static struct delayed_work kfence_timer;
601 static void toggle_allocation_gate(struct work_struct *work)
603 if (!READ_ONCE(kfence_enabled))
606 /* Enable static key, and await allocation to happen. */
607 atomic_set(&kfence_allocation_gate, 0);
608 #ifdef CONFIG_KFENCE_STATIC_KEYS
609 static_branch_enable(&kfence_allocation_key);
611 * Await an allocation. Timeout after 1 second, in case the kernel stops
612 * doing allocations, to avoid stalling this worker task for too long.
615 unsigned long end_wait = jiffies + HZ;
618 set_current_state(TASK_UNINTERRUPTIBLE);
619 if (atomic_read(&kfence_allocation_gate) != 0)
622 } while (time_before(jiffies, end_wait));
623 __set_current_state(TASK_RUNNING);
625 /* Disable static key and reset timer. */
626 static_branch_disable(&kfence_allocation_key);
628 schedule_delayed_work(&kfence_timer, msecs_to_jiffies(kfence_sample_interval));
630 static DECLARE_DELAYED_WORK(kfence_timer, toggle_allocation_gate);
632 /* === Public interface ===================================================== */
634 void __init kfence_alloc_pool(void)
636 if (!kfence_sample_interval)
639 __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
642 pr_err("failed to allocate pool\n");
645 void __init kfence_init(void)
647 /* Setting kfence_sample_interval to 0 on boot disables KFENCE. */
648 if (!kfence_sample_interval)
651 if (!kfence_init_pool()) {
652 pr_err("%s failed\n", __func__);
656 WRITE_ONCE(kfence_enabled, true);
657 schedule_delayed_work(&kfence_timer, 0);
658 pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE,
659 CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool,
660 (void *)(__kfence_pool + KFENCE_POOL_SIZE));
663 void kfence_shutdown_cache(struct kmem_cache *s)
666 struct kfence_metadata *meta;
669 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
672 meta = &kfence_metadata[i];
675 * If we observe some inconsistent cache and state pair where we
676 * should have returned false here, cache destruction is racing
677 * with either kmem_cache_alloc() or kmem_cache_free(). Taking
678 * the lock will not help, as different critical section
679 * serialization will have the same outcome.
681 if (READ_ONCE(meta->cache) != s ||
682 READ_ONCE(meta->state) != KFENCE_OBJECT_ALLOCATED)
685 raw_spin_lock_irqsave(&meta->lock, flags);
686 in_use = meta->cache == s && meta->state == KFENCE_OBJECT_ALLOCATED;
687 raw_spin_unlock_irqrestore(&meta->lock, flags);
691 * This cache still has allocations, and we should not
692 * release them back into the freelist so they can still
693 * safely be used and retain the kernel's default
694 * behaviour of keeping the allocations alive (leak the
695 * cache); however, they effectively become "zombie
696 * allocations" as the KFENCE objects are the only ones
697 * still in use and the owning cache is being destroyed.
699 * We mark them freed, so that any subsequent use shows
700 * more useful error messages that will include stack
701 * traces of the user of the object, the original
702 * allocation, and caller to shutdown_cache().
704 kfence_guarded_free((void *)meta->addr, meta, /*zombie=*/true);
708 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
709 meta = &kfence_metadata[i];
712 if (READ_ONCE(meta->cache) != s || READ_ONCE(meta->state) != KFENCE_OBJECT_FREED)
715 raw_spin_lock_irqsave(&meta->lock, flags);
716 if (meta->cache == s && meta->state == KFENCE_OBJECT_FREED)
718 raw_spin_unlock_irqrestore(&meta->lock, flags);
722 void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
725 * allocation_gate only needs to become non-zero, so it doesn't make
726 * sense to continue writing to it and pay the associated contention
727 * cost, in case we have a large number of concurrent allocations.
729 if (atomic_read(&kfence_allocation_gate) || atomic_inc_return(&kfence_allocation_gate) > 1)
732 if (!READ_ONCE(kfence_enabled))
735 if (size > PAGE_SIZE)
738 return kfence_guarded_alloc(s, size, flags);
741 size_t kfence_ksize(const void *addr)
743 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
746 * Read locklessly -- if there is a race with __kfence_alloc(), this is
747 * either a use-after-free or invalid access.
749 return meta ? meta->size : 0;
752 void *kfence_object_start(const void *addr)
754 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
757 * Read locklessly -- if there is a race with __kfence_alloc(), this is
758 * either a use-after-free or invalid access.
760 return meta ? (void *)meta->addr : NULL;
763 void __kfence_free(void *addr)
765 struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
768 * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing
769 * the object, as the object page may be recycled for other-typed
770 * objects once it has been freed. meta->cache may be NULL if the cache
773 if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU)))
774 call_rcu(&meta->rcu_head, rcu_guarded_free);
776 kfence_guarded_free(addr, meta, false);
779 bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs)
781 const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE;
782 struct kfence_metadata *to_report = NULL;
783 enum kfence_error_type error_type;
786 if (!is_kfence_address((void *)addr))
789 if (!READ_ONCE(kfence_enabled)) /* If disabled at runtime ... */
790 return kfence_unprotect(addr); /* ... unprotect and proceed. */
792 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
794 if (page_index % 2) {
795 /* This is a redzone, report a buffer overflow. */
796 struct kfence_metadata *meta;
799 meta = addr_to_metadata(addr - PAGE_SIZE);
800 if (meta && READ_ONCE(meta->state) == KFENCE_OBJECT_ALLOCATED) {
802 /* Data race ok; distance calculation approximate. */
803 distance = addr - data_race(meta->addr + meta->size);
806 meta = addr_to_metadata(addr + PAGE_SIZE);
807 if (meta && READ_ONCE(meta->state) == KFENCE_OBJECT_ALLOCATED) {
808 /* Data race ok; distance calculation approximate. */
809 if (!to_report || distance > data_race(meta->addr) - addr)
816 raw_spin_lock_irqsave(&to_report->lock, flags);
817 to_report->unprotected_page = addr;
818 error_type = KFENCE_ERROR_OOB;
821 * If the object was freed before we took the look we can still
822 * report this as an OOB -- the report will simply show the
823 * stacktrace of the free as well.
826 to_report = addr_to_metadata(addr);
830 raw_spin_lock_irqsave(&to_report->lock, flags);
831 error_type = KFENCE_ERROR_UAF;
833 * We may race with __kfence_alloc(), and it is possible that a
834 * freed object may be reallocated. We simply report this as a
835 * use-after-free, with the stack trace showing the place where
836 * the object was re-allocated.
842 kfence_report_error(addr, is_write, regs, to_report, error_type);
843 raw_spin_unlock_irqrestore(&to_report->lock, flags);
845 /* This may be a UAF or OOB access, but we can't be sure. */
846 kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID);
849 return kfence_unprotect(addr); /* Unprotect and let access proceed. */