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/irq_work.h>
14 #include <linux/kcsan-checks.h>
15 #include <linux/kfence.h>
16 #include <linux/kmemleak.h>
17 #include <linux/list.h>
18 #include <linux/lockdep.h>
19 #include <linux/memblock.h>
20 #include <linux/moduleparam.h>
21 #include <linux/random.h>
22 #include <linux/rcupdate.h>
23 #include <linux/sched/sysctl.h>
24 #include <linux/seq_file.h>
25 #include <linux/slab.h>
26 #include <linux/spinlock.h>
27 #include <linux/string.h>
29 #include <asm/kfence.h>
33 /* Disables KFENCE on the first warning assuming an irrecoverable error. */
34 #define KFENCE_WARN_ON(cond) \
36 const bool __cond = WARN_ON(cond); \
37 if (unlikely(__cond)) \
38 WRITE_ONCE(kfence_enabled, false); \
42 /* === Data ================================================================= */
44 static bool kfence_enabled __read_mostly;
46 static unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL;
48 #ifdef MODULE_PARAM_PREFIX
49 #undef MODULE_PARAM_PREFIX
51 #define MODULE_PARAM_PREFIX "kfence."
53 static int param_set_sample_interval(const char *val, const struct kernel_param *kp)
56 int ret = kstrtoul(val, 0, &num);
61 if (!num) /* Using 0 to indicate KFENCE is disabled. */
62 WRITE_ONCE(kfence_enabled, false);
63 else if (!READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING)
64 return -EINVAL; /* Cannot (re-)enable KFENCE on-the-fly. */
66 *((unsigned long *)kp->arg) = num;
70 static int param_get_sample_interval(char *buffer, const struct kernel_param *kp)
72 if (!READ_ONCE(kfence_enabled))
73 return sprintf(buffer, "0\n");
75 return param_get_ulong(buffer, kp);
78 static const struct kernel_param_ops sample_interval_param_ops = {
79 .set = param_set_sample_interval,
80 .get = param_get_sample_interval,
82 module_param_cb(sample_interval, &sample_interval_param_ops, &kfence_sample_interval, 0600);
84 /* The pool of pages used for guard pages and objects. */
85 char *__kfence_pool __ro_after_init;
86 EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */
89 * Per-object metadata, with one-to-one mapping of object metadata to
90 * backing pages (in __kfence_pool).
92 static_assert(CONFIG_KFENCE_NUM_OBJECTS > 0);
93 struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
95 /* Freelist with available objects. */
96 static struct list_head kfence_freelist = LIST_HEAD_INIT(kfence_freelist);
97 static DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */
99 #ifdef CONFIG_KFENCE_STATIC_KEYS
100 /* The static key to set up a KFENCE allocation. */
101 DEFINE_STATIC_KEY_FALSE(kfence_allocation_key);
104 /* Gates the allocation, ensuring only one succeeds in a given period. */
105 atomic_t kfence_allocation_gate = ATOMIC_INIT(1);
107 /* Statistics counters for debugfs. */
108 enum kfence_counter_id {
109 KFENCE_COUNTER_ALLOCATED,
110 KFENCE_COUNTER_ALLOCS,
111 KFENCE_COUNTER_FREES,
112 KFENCE_COUNTER_ZOMBIES,
114 KFENCE_COUNTER_COUNT,
116 static atomic_long_t counters[KFENCE_COUNTER_COUNT];
117 static const char *const counter_names[] = {
118 [KFENCE_COUNTER_ALLOCATED] = "currently allocated",
119 [KFENCE_COUNTER_ALLOCS] = "total allocations",
120 [KFENCE_COUNTER_FREES] = "total frees",
121 [KFENCE_COUNTER_ZOMBIES] = "zombie allocations",
122 [KFENCE_COUNTER_BUGS] = "total bugs",
124 static_assert(ARRAY_SIZE(counter_names) == KFENCE_COUNTER_COUNT);
126 /* === Internals ============================================================ */
128 static bool kfence_protect(unsigned long addr)
130 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), true));
133 static bool kfence_unprotect(unsigned long addr)
135 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), false));
138 static inline struct kfence_metadata *addr_to_metadata(unsigned long addr)
142 /* The checks do not affect performance; only called from slow-paths. */
144 if (!is_kfence_address((void *)addr))
148 * May be an invalid index if called with an address at the edge of
149 * __kfence_pool, in which case we would report an "invalid access"
152 index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1;
153 if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS)
156 return &kfence_metadata[index];
159 static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta)
161 unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2;
162 unsigned long pageaddr = (unsigned long)&__kfence_pool[offset];
164 /* The checks do not affect performance; only called from slow-paths. */
166 /* Only call with a pointer into kfence_metadata. */
167 if (KFENCE_WARN_ON(meta < kfence_metadata ||
168 meta >= kfence_metadata + CONFIG_KFENCE_NUM_OBJECTS))
172 * This metadata object only ever maps to 1 page; verify that the stored
173 * address is in the expected range.
175 if (KFENCE_WARN_ON(ALIGN_DOWN(meta->addr, PAGE_SIZE) != pageaddr))
182 * Update the object's metadata state, including updating the alloc/free stacks
183 * depending on the state transition.
185 static noinline void metadata_update_state(struct kfence_metadata *meta,
186 enum kfence_object_state next)
188 struct kfence_track *track =
189 next == KFENCE_OBJECT_FREED ? &meta->free_track : &meta->alloc_track;
191 lockdep_assert_held(&meta->lock);
194 * Skip over 1 (this) functions; noinline ensures we do not accidentally
195 * skip over the caller by never inlining.
197 track->num_stack_entries = stack_trace_save(track->stack_entries, KFENCE_STACK_DEPTH, 1);
198 track->pid = task_pid_nr(current);
201 * Pairs with READ_ONCE() in
202 * kfence_shutdown_cache(),
203 * kfence_handle_page_fault().
205 WRITE_ONCE(meta->state, next);
208 /* Write canary byte to @addr. */
209 static inline bool set_canary_byte(u8 *addr)
211 *addr = KFENCE_CANARY_PATTERN(addr);
215 /* Check canary byte at @addr. */
216 static inline bool check_canary_byte(u8 *addr)
218 if (likely(*addr == KFENCE_CANARY_PATTERN(addr)))
221 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
222 kfence_report_error((unsigned long)addr, false, NULL, addr_to_metadata((unsigned long)addr),
223 KFENCE_ERROR_CORRUPTION);
227 /* __always_inline this to ensure we won't do an indirect call to fn. */
228 static __always_inline void for_each_canary(const struct kfence_metadata *meta, bool (*fn)(u8 *))
230 const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE);
233 lockdep_assert_held(&meta->lock);
236 * We'll iterate over each canary byte per-side until fn() returns
237 * false. However, we'll still iterate over the canary bytes to the
238 * right of the object even if there was an error in the canary bytes to
239 * the left of the object. Specifically, if check_canary_byte()
240 * generates an error, showing both sides might give more clues as to
241 * what the error is about when displaying which bytes were corrupted.
244 /* Apply to left of object. */
245 for (addr = pageaddr; addr < meta->addr; addr++) {
250 /* Apply to right of object. */
251 for (addr = meta->addr + meta->size; addr < pageaddr + PAGE_SIZE; addr++) {
257 static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t gfp)
259 struct kfence_metadata *meta = NULL;
264 /* Try to obtain a free object. */
265 raw_spin_lock_irqsave(&kfence_freelist_lock, flags);
266 if (!list_empty(&kfence_freelist)) {
267 meta = list_entry(kfence_freelist.next, struct kfence_metadata, list);
268 list_del_init(&meta->list);
270 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);
274 if (unlikely(!raw_spin_trylock_irqsave(&meta->lock, flags))) {
276 * This is extremely unlikely -- we are reporting on a
277 * use-after-free, which locked meta->lock, and the reporting
278 * code via printk calls kmalloc() which ends up in
279 * kfence_alloc() and tries to grab the same object that we're
280 * reporting on. While it has never been observed, lockdep does
281 * report that there is a possibility of deadlock. Fix it by
282 * using trylock and bailing out gracefully.
284 raw_spin_lock_irqsave(&kfence_freelist_lock, flags);
285 /* Put the object back on the freelist. */
286 list_add_tail(&meta->list, &kfence_freelist);
287 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);
292 meta->addr = metadata_to_pageaddr(meta);
293 /* Unprotect if we're reusing this page. */
294 if (meta->state == KFENCE_OBJECT_FREED)
295 kfence_unprotect(meta->addr);
298 * Note: for allocations made before RNG initialization, will always
299 * return zero. We still benefit from enabling KFENCE as early as
300 * possible, even when the RNG is not yet available, as this will allow
301 * KFENCE to detect bugs due to earlier allocations. The only downside
302 * is that the out-of-bounds accesses detected are deterministic for
305 if (prandom_u32_max(2)) {
306 /* Allocate on the "right" side, re-calculate address. */
307 meta->addr += PAGE_SIZE - size;
308 meta->addr = ALIGN_DOWN(meta->addr, cache->align);
311 addr = (void *)meta->addr;
313 /* Update remaining metadata. */
314 metadata_update_state(meta, KFENCE_OBJECT_ALLOCATED);
315 /* Pairs with READ_ONCE() in kfence_shutdown_cache(). */
316 WRITE_ONCE(meta->cache, cache);
318 for_each_canary(meta, set_canary_byte);
320 /* Set required struct page fields. */
321 page = virt_to_page(meta->addr);
322 page->slab_cache = cache;
323 if (IS_ENABLED(CONFIG_SLUB))
325 if (IS_ENABLED(CONFIG_SLAB))
328 raw_spin_unlock_irqrestore(&meta->lock, flags);
330 /* Memory initialization. */
333 * We check slab_want_init_on_alloc() ourselves, rather than letting
334 * SL*B do the initialization, as otherwise we might overwrite KFENCE's
337 if (unlikely(slab_want_init_on_alloc(gfp, cache)))
338 memzero_explicit(addr, size);
342 if (CONFIG_KFENCE_STRESS_TEST_FAULTS && !prandom_u32_max(CONFIG_KFENCE_STRESS_TEST_FAULTS))
343 kfence_protect(meta->addr); /* Random "faults" by protecting the object. */
345 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCATED]);
346 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCS]);
351 static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool zombie)
353 struct kcsan_scoped_access assert_page_exclusive;
356 raw_spin_lock_irqsave(&meta->lock, flags);
358 if (meta->state != KFENCE_OBJECT_ALLOCATED || meta->addr != (unsigned long)addr) {
359 /* Invalid or double-free, bail out. */
360 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
361 kfence_report_error((unsigned long)addr, false, NULL, meta,
362 KFENCE_ERROR_INVALID_FREE);
363 raw_spin_unlock_irqrestore(&meta->lock, flags);
367 /* Detect racy use-after-free, or incorrect reallocation of this page by KFENCE. */
368 kcsan_begin_scoped_access((void *)ALIGN_DOWN((unsigned long)addr, PAGE_SIZE), PAGE_SIZE,
369 KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT,
370 &assert_page_exclusive);
372 if (CONFIG_KFENCE_STRESS_TEST_FAULTS)
373 kfence_unprotect((unsigned long)addr); /* To check canary bytes. */
375 /* Restore page protection if there was an OOB access. */
376 if (meta->unprotected_page) {
377 memzero_explicit((void *)ALIGN_DOWN(meta->unprotected_page, PAGE_SIZE), PAGE_SIZE);
378 kfence_protect(meta->unprotected_page);
379 meta->unprotected_page = 0;
382 /* Check canary bytes for memory corruption. */
383 for_each_canary(meta, check_canary_byte);
386 * Clear memory if init-on-free is set. While we protect the page, the
387 * data is still there, and after a use-after-free is detected, we
388 * unprotect the page, so the data is still accessible.
390 if (!zombie && unlikely(slab_want_init_on_free(meta->cache)))
391 memzero_explicit(addr, meta->size);
393 /* Mark the object as freed. */
394 metadata_update_state(meta, KFENCE_OBJECT_FREED);
396 raw_spin_unlock_irqrestore(&meta->lock, flags);
398 /* Protect to detect use-after-frees. */
399 kfence_protect((unsigned long)addr);
401 kcsan_end_scoped_access(&assert_page_exclusive);
403 /* Add it to the tail of the freelist for reuse. */
404 raw_spin_lock_irqsave(&kfence_freelist_lock, flags);
405 KFENCE_WARN_ON(!list_empty(&meta->list));
406 list_add_tail(&meta->list, &kfence_freelist);
407 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);
409 atomic_long_dec(&counters[KFENCE_COUNTER_ALLOCATED]);
410 atomic_long_inc(&counters[KFENCE_COUNTER_FREES]);
412 /* See kfence_shutdown_cache(). */
413 atomic_long_inc(&counters[KFENCE_COUNTER_ZOMBIES]);
417 static void rcu_guarded_free(struct rcu_head *h)
419 struct kfence_metadata *meta = container_of(h, struct kfence_metadata, rcu_head);
421 kfence_guarded_free((void *)meta->addr, meta, false);
424 static bool __init kfence_init_pool(void)
426 unsigned long addr = (unsigned long)__kfence_pool;
433 if (!arch_kfence_init_pool())
436 pages = virt_to_page(addr);
439 * Set up object pages: they must have PG_slab set, to avoid freeing
440 * these as real pages.
442 * We also want to avoid inserting kfence_free() in the kfree()
443 * fast-path in SLUB, and therefore need to ensure kfree() correctly
444 * enters __slab_free() slow-path.
446 for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
450 /* Verify we do not have a compound head page. */
451 if (WARN_ON(compound_head(&pages[i]) != &pages[i]))
454 __SetPageSlab(&pages[i]);
458 * Protect the first 2 pages. The first page is mostly unnecessary, and
459 * merely serves as an extended guard page. However, adding one
460 * additional page in the beginning gives us an even number of pages,
461 * which simplifies the mapping of address to metadata index.
463 for (i = 0; i < 2; i++) {
464 if (unlikely(!kfence_protect(addr)))
470 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
471 struct kfence_metadata *meta = &kfence_metadata[i];
473 /* Initialize metadata. */
474 INIT_LIST_HEAD(&meta->list);
475 raw_spin_lock_init(&meta->lock);
476 meta->state = KFENCE_OBJECT_UNUSED;
477 meta->addr = addr; /* Initialize for validation in metadata_to_pageaddr(). */
478 list_add_tail(&meta->list, &kfence_freelist);
480 /* Protect the right redzone. */
481 if (unlikely(!kfence_protect(addr + PAGE_SIZE)))
484 addr += 2 * PAGE_SIZE;
488 * The pool is live and will never be deallocated from this point on.
489 * Remove the pool object from the kmemleak object tree, as it would
490 * otherwise overlap with allocations returned by kfence_alloc(), which
491 * are registered with kmemleak through the slab post-alloc hook.
493 kmemleak_free(__kfence_pool);
499 * Only release unprotected pages, and do not try to go back and change
500 * page attributes due to risk of failing to do so as well. If changing
501 * page attributes for some pages fails, it is very likely that it also
502 * fails for the first page, and therefore expect addr==__kfence_pool in
503 * most failure cases.
505 memblock_free_late(__pa(addr), KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool));
506 __kfence_pool = NULL;
510 /* === DebugFS Interface ==================================================== */
512 static int stats_show(struct seq_file *seq, void *v)
516 seq_printf(seq, "enabled: %i\n", READ_ONCE(kfence_enabled));
517 for (i = 0; i < KFENCE_COUNTER_COUNT; i++)
518 seq_printf(seq, "%s: %ld\n", counter_names[i], atomic_long_read(&counters[i]));
522 DEFINE_SHOW_ATTRIBUTE(stats);
525 * debugfs seq_file operations for /sys/kernel/debug/kfence/objects.
526 * start_object() and next_object() return the object index + 1, because NULL is used
529 static void *start_object(struct seq_file *seq, loff_t *pos)
531 if (*pos < CONFIG_KFENCE_NUM_OBJECTS)
532 return (void *)((long)*pos + 1);
536 static void stop_object(struct seq_file *seq, void *v)
540 static void *next_object(struct seq_file *seq, void *v, loff_t *pos)
543 if (*pos < CONFIG_KFENCE_NUM_OBJECTS)
544 return (void *)((long)*pos + 1);
548 static int show_object(struct seq_file *seq, void *v)
550 struct kfence_metadata *meta = &kfence_metadata[(long)v - 1];
553 raw_spin_lock_irqsave(&meta->lock, flags);
554 kfence_print_object(seq, meta);
555 raw_spin_unlock_irqrestore(&meta->lock, flags);
556 seq_puts(seq, "---------------------------------\n");
561 static const struct seq_operations object_seqops = {
562 .start = start_object,
568 static int open_objects(struct inode *inode, struct file *file)
570 return seq_open(file, &object_seqops);
573 static const struct file_operations objects_fops = {
574 .open = open_objects,
579 static int __init kfence_debugfs_init(void)
581 struct dentry *kfence_dir = debugfs_create_dir("kfence", NULL);
583 debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops);
584 debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops);
588 late_initcall(kfence_debugfs_init);
590 /* === Allocation Gate Timer ================================================ */
592 #ifdef CONFIG_KFENCE_STATIC_KEYS
593 /* Wait queue to wake up allocation-gate timer task. */
594 static DECLARE_WAIT_QUEUE_HEAD(allocation_wait);
596 static void wake_up_kfence_timer(struct irq_work *work)
598 wake_up(&allocation_wait);
600 static DEFINE_IRQ_WORK(wake_up_kfence_timer_work, wake_up_kfence_timer);
604 * Set up delayed work, which will enable and disable the static key. We need to
605 * use a work queue (rather than a simple timer), since enabling and disabling a
606 * static key cannot be done from an interrupt.
608 * Note: Toggling a static branch currently causes IPIs, and here we'll end up
609 * with a total of 2 IPIs to all CPUs. If this ends up a problem in future (with
610 * more aggressive sampling intervals), we could get away with a variant that
611 * avoids IPIs, at the cost of not immediately capturing allocations if the
612 * instructions remain cached.
614 static struct delayed_work kfence_timer;
615 static void toggle_allocation_gate(struct work_struct *work)
617 if (!READ_ONCE(kfence_enabled))
620 atomic_set(&kfence_allocation_gate, 0);
621 #ifdef CONFIG_KFENCE_STATIC_KEYS
622 /* Enable static key, and await allocation to happen. */
623 static_branch_enable(&kfence_allocation_key);
625 if (sysctl_hung_task_timeout_secs) {
627 * During low activity with no allocations we might wait a
628 * while; let's avoid the hung task warning.
630 wait_event_timeout(allocation_wait, atomic_read(&kfence_allocation_gate),
631 sysctl_hung_task_timeout_secs * HZ / 2);
633 wait_event(allocation_wait, atomic_read(&kfence_allocation_gate));
636 /* Disable static key and reset timer. */
637 static_branch_disable(&kfence_allocation_key);
639 queue_delayed_work(system_power_efficient_wq, &kfence_timer,
640 msecs_to_jiffies(kfence_sample_interval));
642 static DECLARE_DELAYED_WORK(kfence_timer, toggle_allocation_gate);
644 /* === Public interface ===================================================== */
646 void __init kfence_alloc_pool(void)
648 if (!kfence_sample_interval)
651 __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
654 pr_err("failed to allocate pool\n");
657 void __init kfence_init(void)
659 /* Setting kfence_sample_interval to 0 on boot disables KFENCE. */
660 if (!kfence_sample_interval)
663 if (!kfence_init_pool()) {
664 pr_err("%s failed\n", __func__);
668 WRITE_ONCE(kfence_enabled, true);
669 queue_delayed_work(system_power_efficient_wq, &kfence_timer, 0);
670 pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE,
671 CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool,
672 (void *)(__kfence_pool + KFENCE_POOL_SIZE));
675 void kfence_shutdown_cache(struct kmem_cache *s)
678 struct kfence_metadata *meta;
681 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
684 meta = &kfence_metadata[i];
687 * If we observe some inconsistent cache and state pair where we
688 * should have returned false here, cache destruction is racing
689 * with either kmem_cache_alloc() or kmem_cache_free(). Taking
690 * the lock will not help, as different critical section
691 * serialization will have the same outcome.
693 if (READ_ONCE(meta->cache) != s ||
694 READ_ONCE(meta->state) != KFENCE_OBJECT_ALLOCATED)
697 raw_spin_lock_irqsave(&meta->lock, flags);
698 in_use = meta->cache == s && meta->state == KFENCE_OBJECT_ALLOCATED;
699 raw_spin_unlock_irqrestore(&meta->lock, flags);
703 * This cache still has allocations, and we should not
704 * release them back into the freelist so they can still
705 * safely be used and retain the kernel's default
706 * behaviour of keeping the allocations alive (leak the
707 * cache); however, they effectively become "zombie
708 * allocations" as the KFENCE objects are the only ones
709 * still in use and the owning cache is being destroyed.
711 * We mark them freed, so that any subsequent use shows
712 * more useful error messages that will include stack
713 * traces of the user of the object, the original
714 * allocation, and caller to shutdown_cache().
716 kfence_guarded_free((void *)meta->addr, meta, /*zombie=*/true);
720 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
721 meta = &kfence_metadata[i];
724 if (READ_ONCE(meta->cache) != s || READ_ONCE(meta->state) != KFENCE_OBJECT_FREED)
727 raw_spin_lock_irqsave(&meta->lock, flags);
728 if (meta->cache == s && meta->state == KFENCE_OBJECT_FREED)
730 raw_spin_unlock_irqrestore(&meta->lock, flags);
734 void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
737 * allocation_gate only needs to become non-zero, so it doesn't make
738 * sense to continue writing to it and pay the associated contention
739 * cost, in case we have a large number of concurrent allocations.
741 if (atomic_read(&kfence_allocation_gate) || atomic_inc_return(&kfence_allocation_gate) > 1)
743 #ifdef CONFIG_KFENCE_STATIC_KEYS
745 * waitqueue_active() is fully ordered after the update of
746 * kfence_allocation_gate per atomic_inc_return().
748 if (waitqueue_active(&allocation_wait)) {
750 * Calling wake_up() here may deadlock when allocations happen
751 * from within timer code. Use an irq_work to defer it.
753 irq_work_queue(&wake_up_kfence_timer_work);
757 if (!READ_ONCE(kfence_enabled))
760 if (size > PAGE_SIZE)
763 return kfence_guarded_alloc(s, size, flags);
766 size_t kfence_ksize(const void *addr)
768 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
771 * Read locklessly -- if there is a race with __kfence_alloc(), this is
772 * either a use-after-free or invalid access.
774 return meta ? meta->size : 0;
777 void *kfence_object_start(const void *addr)
779 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
782 * Read locklessly -- if there is a race with __kfence_alloc(), this is
783 * either a use-after-free or invalid access.
785 return meta ? (void *)meta->addr : NULL;
788 void __kfence_free(void *addr)
790 struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
793 * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing
794 * the object, as the object page may be recycled for other-typed
795 * objects once it has been freed. meta->cache may be NULL if the cache
798 if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU)))
799 call_rcu(&meta->rcu_head, rcu_guarded_free);
801 kfence_guarded_free(addr, meta, false);
804 bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs)
806 const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE;
807 struct kfence_metadata *to_report = NULL;
808 enum kfence_error_type error_type;
811 if (!is_kfence_address((void *)addr))
814 if (!READ_ONCE(kfence_enabled)) /* If disabled at runtime ... */
815 return kfence_unprotect(addr); /* ... unprotect and proceed. */
817 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
819 if (page_index % 2) {
820 /* This is a redzone, report a buffer overflow. */
821 struct kfence_metadata *meta;
824 meta = addr_to_metadata(addr - PAGE_SIZE);
825 if (meta && READ_ONCE(meta->state) == KFENCE_OBJECT_ALLOCATED) {
827 /* Data race ok; distance calculation approximate. */
828 distance = addr - data_race(meta->addr + meta->size);
831 meta = addr_to_metadata(addr + PAGE_SIZE);
832 if (meta && READ_ONCE(meta->state) == KFENCE_OBJECT_ALLOCATED) {
833 /* Data race ok; distance calculation approximate. */
834 if (!to_report || distance > data_race(meta->addr) - addr)
841 raw_spin_lock_irqsave(&to_report->lock, flags);
842 to_report->unprotected_page = addr;
843 error_type = KFENCE_ERROR_OOB;
846 * If the object was freed before we took the look we can still
847 * report this as an OOB -- the report will simply show the
848 * stacktrace of the free as well.
851 to_report = addr_to_metadata(addr);
855 raw_spin_lock_irqsave(&to_report->lock, flags);
856 error_type = KFENCE_ERROR_UAF;
858 * We may race with __kfence_alloc(), and it is possible that a
859 * freed object may be reallocated. We simply report this as a
860 * use-after-free, with the stack trace showing the place where
861 * the object was re-allocated.
867 kfence_report_error(addr, is_write, regs, to_report, error_type);
868 raw_spin_unlock_irqrestore(&to_report->lock, flags);
870 /* This may be a UAF or OOB access, but we can't be sure. */
871 kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID);
874 return kfence_unprotect(addr); /* Unprotect and let access proceed. */