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Linux/mm/kasan/common.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * This file contains common generic and tag-based KASAN code.
  4  *
  5  * Copyright (c) 2014 Samsung Electronics Co., Ltd.
  6  * Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
  7  *
  8  * Some code borrowed from https://github.com/xairy/kasan-prototype by
  9  *        Andrey Konovalov <andreyknvl@gmail.com>
 10  *
 11  * This program is free software; you can redistribute it and/or modify
 12  * it under the terms of the GNU General Public License version 2 as
 13  * published by the Free Software Foundation.
 14  *
 15  */
 16 
 17 #include <linux/export.h>
 18 #include <linux/init.h>
 19 #include <linux/kasan.h>
 20 #include <linux/kernel.h>
 21 #include <linux/kmemleak.h>
 22 #include <linux/linkage.h>
 23 #include <linux/memblock.h>
 24 #include <linux/memory.h>
 25 #include <linux/mm.h>
 26 #include <linux/module.h>
 27 #include <linux/printk.h>
 28 #include <linux/sched.h>
 29 #include <linux/sched/task_stack.h>
 30 #include <linux/slab.h>
 31 #include <linux/stacktrace.h>
 32 #include <linux/string.h>
 33 #include <linux/types.h>
 34 #include <linux/vmalloc.h>
 35 #include <linux/bug.h>
 36 
 37 #include <asm/cacheflush.h>
 38 #include <asm/tlbflush.h>
 39 
 40 #include "kasan.h"
 41 #include "../slab.h"
 42 
 43 depot_stack_handle_t kasan_save_stack(gfp_t flags)
 44 {
 45         unsigned long entries[KASAN_STACK_DEPTH];
 46         unsigned int nr_entries;
 47 
 48         nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
 49         nr_entries = filter_irq_stacks(entries, nr_entries);
 50         return stack_depot_save(entries, nr_entries, flags);
 51 }
 52 
 53 void kasan_set_track(struct kasan_track *track, gfp_t flags)
 54 {
 55         track->pid = current->pid;
 56         track->stack = kasan_save_stack(flags);
 57 }
 58 
 59 void kasan_enable_current(void)
 60 {
 61         current->kasan_depth++;
 62 }
 63 
 64 void kasan_disable_current(void)
 65 {
 66         current->kasan_depth--;
 67 }
 68 
 69 bool __kasan_check_read(const volatile void *p, unsigned int size)
 70 {
 71         return check_memory_region((unsigned long)p, size, false, _RET_IP_);
 72 }
 73 EXPORT_SYMBOL(__kasan_check_read);
 74 
 75 bool __kasan_check_write(const volatile void *p, unsigned int size)
 76 {
 77         return check_memory_region((unsigned long)p, size, true, _RET_IP_);
 78 }
 79 EXPORT_SYMBOL(__kasan_check_write);
 80 
 81 #undef memset
 82 void *memset(void *addr, int c, size_t len)
 83 {
 84         if (!check_memory_region((unsigned long)addr, len, true, _RET_IP_))
 85                 return NULL;
 86 
 87         return __memset(addr, c, len);
 88 }
 89 
 90 #ifdef __HAVE_ARCH_MEMMOVE
 91 #undef memmove
 92 void *memmove(void *dest, const void *src, size_t len)
 93 {
 94         if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
 95             !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
 96                 return NULL;
 97 
 98         return __memmove(dest, src, len);
 99 }
100 #endif
101 
102 #undef memcpy
103 void *memcpy(void *dest, const void *src, size_t len)
104 {
105         if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
106             !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
107                 return NULL;
108 
109         return __memcpy(dest, src, len);
110 }
111 
112 /*
113  * Poisons the shadow memory for 'size' bytes starting from 'addr'.
114  * Memory addresses should be aligned to KASAN_SHADOW_SCALE_SIZE.
115  */
116 void kasan_poison_shadow(const void *address, size_t size, u8 value)
117 {
118         void *shadow_start, *shadow_end;
119 
120         /*
121          * Perform shadow offset calculation based on untagged address, as
122          * some of the callers (e.g. kasan_poison_object_data) pass tagged
123          * addresses to this function.
124          */
125         address = reset_tag(address);
126 
127         shadow_start = kasan_mem_to_shadow(address);
128         shadow_end = kasan_mem_to_shadow(address + size);
129 
130         __memset(shadow_start, value, shadow_end - shadow_start);
131 }
132 
133 void kasan_unpoison_shadow(const void *address, size_t size)
134 {
135         u8 tag = get_tag(address);
136 
137         /*
138          * Perform shadow offset calculation based on untagged address, as
139          * some of the callers (e.g. kasan_unpoison_object_data) pass tagged
140          * addresses to this function.
141          */
142         address = reset_tag(address);
143 
144         kasan_poison_shadow(address, size, tag);
145 
146         if (size & KASAN_SHADOW_MASK) {
147                 u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
148 
149                 if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
150                         *shadow = tag;
151                 else
152                         *shadow = size & KASAN_SHADOW_MASK;
153         }
154 }
155 
156 static void __kasan_unpoison_stack(struct task_struct *task, const void *sp)
157 {
158         void *base = task_stack_page(task);
159         size_t size = sp - base;
160 
161         kasan_unpoison_shadow(base, size);
162 }
163 
164 /* Unpoison the entire stack for a task. */
165 void kasan_unpoison_task_stack(struct task_struct *task)
166 {
167         __kasan_unpoison_stack(task, task_stack_page(task) + THREAD_SIZE);
168 }
169 
170 /* Unpoison the stack for the current task beyond a watermark sp value. */
171 asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
172 {
173         /*
174          * Calculate the task stack base address.  Avoid using 'current'
175          * because this function is called by early resume code which hasn't
176          * yet set up the percpu register (%gs).
177          */
178         void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1));
179 
180         kasan_unpoison_shadow(base, watermark - base);
181 }
182 
183 void kasan_alloc_pages(struct page *page, unsigned int order)
184 {
185         u8 tag;
186         unsigned long i;
187 
188         if (unlikely(PageHighMem(page)))
189                 return;
190 
191         tag = random_tag();
192         for (i = 0; i < (1 << order); i++)
193                 page_kasan_tag_set(page + i, tag);
194         kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
195 }
196 
197 void kasan_free_pages(struct page *page, unsigned int order)
198 {
199         if (likely(!PageHighMem(page)))
200                 kasan_poison_shadow(page_address(page),
201                                 PAGE_SIZE << order,
202                                 KASAN_FREE_PAGE);
203 }
204 
205 /*
206  * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
207  * For larger allocations larger redzones are used.
208  */
209 static inline unsigned int optimal_redzone(unsigned int object_size)
210 {
211         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
212                 return 0;
213 
214         return
215                 object_size <= 64        - 16   ? 16 :
216                 object_size <= 128       - 32   ? 32 :
217                 object_size <= 512       - 64   ? 64 :
218                 object_size <= 4096      - 128  ? 128 :
219                 object_size <= (1 << 14) - 256  ? 256 :
220                 object_size <= (1 << 15) - 512  ? 512 :
221                 object_size <= (1 << 16) - 1024 ? 1024 : 2048;
222 }
223 
224 void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
225                         slab_flags_t *flags)
226 {
227         unsigned int orig_size = *size;
228         unsigned int redzone_size;
229         int redzone_adjust;
230 
231         /* Add alloc meta. */
232         cache->kasan_info.alloc_meta_offset = *size;
233         *size += sizeof(struct kasan_alloc_meta);
234 
235         /* Add free meta. */
236         if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
237             (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
238              cache->object_size < sizeof(struct kasan_free_meta))) {
239                 cache->kasan_info.free_meta_offset = *size;
240                 *size += sizeof(struct kasan_free_meta);
241         }
242 
243         redzone_size = optimal_redzone(cache->object_size);
244         redzone_adjust = redzone_size - (*size - cache->object_size);
245         if (redzone_adjust > 0)
246                 *size += redzone_adjust;
247 
248         *size = min_t(unsigned int, KMALLOC_MAX_SIZE,
249                         max(*size, cache->object_size + redzone_size));
250 
251         /*
252          * If the metadata doesn't fit, don't enable KASAN at all.
253          */
254         if (*size <= cache->kasan_info.alloc_meta_offset ||
255                         *size <= cache->kasan_info.free_meta_offset) {
256                 cache->kasan_info.alloc_meta_offset = 0;
257                 cache->kasan_info.free_meta_offset = 0;
258                 *size = orig_size;
259                 return;
260         }
261 
262         *flags |= SLAB_KASAN;
263 }
264 
265 size_t kasan_metadata_size(struct kmem_cache *cache)
266 {
267         return (cache->kasan_info.alloc_meta_offset ?
268                 sizeof(struct kasan_alloc_meta) : 0) +
269                 (cache->kasan_info.free_meta_offset ?
270                 sizeof(struct kasan_free_meta) : 0);
271 }
272 
273 struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
274                                         const void *object)
275 {
276         return (void *)object + cache->kasan_info.alloc_meta_offset;
277 }
278 
279 struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
280                                       const void *object)
281 {
282         BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
283         return (void *)object + cache->kasan_info.free_meta_offset;
284 }
285 
286 void kasan_poison_slab(struct page *page)
287 {
288         unsigned long i;
289 
290         for (i = 0; i < compound_nr(page); i++)
291                 page_kasan_tag_reset(page + i);
292         kasan_poison_shadow(page_address(page), page_size(page),
293                         KASAN_KMALLOC_REDZONE);
294 }
295 
296 void kasan_unpoison_object_data(struct kmem_cache *cache, void *object)
297 {
298         kasan_unpoison_shadow(object, cache->object_size);
299 }
300 
301 void kasan_poison_object_data(struct kmem_cache *cache, void *object)
302 {
303         kasan_poison_shadow(object,
304                         round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE),
305                         KASAN_KMALLOC_REDZONE);
306 }
307 
308 /*
309  * This function assigns a tag to an object considering the following:
310  * 1. A cache might have a constructor, which might save a pointer to a slab
311  *    object somewhere (e.g. in the object itself). We preassign a tag for
312  *    each object in caches with constructors during slab creation and reuse
313  *    the same tag each time a particular object is allocated.
314  * 2. A cache might be SLAB_TYPESAFE_BY_RCU, which means objects can be
315  *    accessed after being freed. We preassign tags for objects in these
316  *    caches as well.
317  * 3. For SLAB allocator we can't preassign tags randomly since the freelist
318  *    is stored as an array of indexes instead of a linked list. Assign tags
319  *    based on objects indexes, so that objects that are next to each other
320  *    get different tags.
321  */
322 static u8 assign_tag(struct kmem_cache *cache, const void *object,
323                         bool init, bool keep_tag)
324 {
325         /*
326          * 1. When an object is kmalloc()'ed, two hooks are called:
327          *    kasan_slab_alloc() and kasan_kmalloc(). We assign the
328          *    tag only in the first one.
329          * 2. We reuse the same tag for krealloc'ed objects.
330          */
331         if (keep_tag)
332                 return get_tag(object);
333 
334         /*
335          * If the cache neither has a constructor nor has SLAB_TYPESAFE_BY_RCU
336          * set, assign a tag when the object is being allocated (init == false).
337          */
338         if (!cache->ctor && !(cache->flags & SLAB_TYPESAFE_BY_RCU))
339                 return init ? KASAN_TAG_KERNEL : random_tag();
340 
341         /* For caches that either have a constructor or SLAB_TYPESAFE_BY_RCU: */
342 #ifdef CONFIG_SLAB
343         /* For SLAB assign tags based on the object index in the freelist. */
344         return (u8)obj_to_index(cache, virt_to_page(object), (void *)object);
345 #else
346         /*
347          * For SLUB assign a random tag during slab creation, otherwise reuse
348          * the already assigned tag.
349          */
350         return init ? random_tag() : get_tag(object);
351 #endif
352 }
353 
354 void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
355                                                 const void *object)
356 {
357         struct kasan_alloc_meta *alloc_info;
358 
359         if (!(cache->flags & SLAB_KASAN))
360                 return (void *)object;
361 
362         alloc_info = get_alloc_info(cache, object);
363         __memset(alloc_info, 0, sizeof(*alloc_info));
364 
365         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
366                 object = set_tag(object,
367                                 assign_tag(cache, object, true, false));
368 
369         return (void *)object;
370 }
371 
372 static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
373 {
374         if (IS_ENABLED(CONFIG_KASAN_GENERIC))
375                 return shadow_byte < 0 ||
376                         shadow_byte >= KASAN_SHADOW_SCALE_SIZE;
377 
378         /* else CONFIG_KASAN_SW_TAGS: */
379         if ((u8)shadow_byte == KASAN_TAG_INVALID)
380                 return true;
381         if ((tag != KASAN_TAG_KERNEL) && (tag != (u8)shadow_byte))
382                 return true;
383 
384         return false;
385 }
386 
387 static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
388                               unsigned long ip, bool quarantine)
389 {
390         s8 shadow_byte;
391         u8 tag;
392         void *tagged_object;
393         unsigned long rounded_up_size;
394 
395         tag = get_tag(object);
396         tagged_object = object;
397         object = reset_tag(object);
398 
399         if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
400             object)) {
401                 kasan_report_invalid_free(tagged_object, ip);
402                 return true;
403         }
404 
405         /* RCU slabs could be legally used after free within the RCU period */
406         if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
407                 return false;
408 
409         shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
410         if (shadow_invalid(tag, shadow_byte)) {
411                 kasan_report_invalid_free(tagged_object, ip);
412                 return true;
413         }
414 
415         rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
416         kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
417 
418         if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
419                         unlikely(!(cache->flags & SLAB_KASAN)))
420                 return false;
421 
422         kasan_set_free_info(cache, object, tag);
423 
424         quarantine_put(get_free_info(cache, object), cache);
425 
426         return IS_ENABLED(CONFIG_KASAN_GENERIC);
427 }
428 
429 bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
430 {
431         return __kasan_slab_free(cache, object, ip, true);
432 }
433 
434 static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object,
435                                 size_t size, gfp_t flags, bool keep_tag)
436 {
437         unsigned long redzone_start;
438         unsigned long redzone_end;
439         u8 tag = 0xff;
440 
441         if (gfpflags_allow_blocking(flags))
442                 quarantine_reduce();
443 
444         if (unlikely(object == NULL))
445                 return NULL;
446 
447         redzone_start = round_up((unsigned long)(object + size),
448                                 KASAN_SHADOW_SCALE_SIZE);
449         redzone_end = round_up((unsigned long)object + cache->object_size,
450                                 KASAN_SHADOW_SCALE_SIZE);
451 
452         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
453                 tag = assign_tag(cache, object, false, keep_tag);
454 
455         /* Tag is ignored in set_tag without CONFIG_KASAN_SW_TAGS */
456         kasan_unpoison_shadow(set_tag(object, tag), size);
457         kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
458                 KASAN_KMALLOC_REDZONE);
459 
460         if (cache->flags & SLAB_KASAN)
461                 kasan_set_track(&get_alloc_info(cache, object)->alloc_track, flags);
462 
463         return set_tag(object, tag);
464 }
465 
466 void * __must_check kasan_slab_alloc(struct kmem_cache *cache, void *object,
467                                         gfp_t flags)
468 {
469         return __kasan_kmalloc(cache, object, cache->object_size, flags, false);
470 }
471 
472 void * __must_check kasan_kmalloc(struct kmem_cache *cache, const void *object,
473                                 size_t size, gfp_t flags)
474 {
475         return __kasan_kmalloc(cache, object, size, flags, true);
476 }
477 EXPORT_SYMBOL(kasan_kmalloc);
478 
479 void * __must_check kasan_kmalloc_large(const void *ptr, size_t size,
480                                                 gfp_t flags)
481 {
482         struct page *page;
483         unsigned long redzone_start;
484         unsigned long redzone_end;
485 
486         if (gfpflags_allow_blocking(flags))
487                 quarantine_reduce();
488 
489         if (unlikely(ptr == NULL))
490                 return NULL;
491 
492         page = virt_to_page(ptr);
493         redzone_start = round_up((unsigned long)(ptr + size),
494                                 KASAN_SHADOW_SCALE_SIZE);
495         redzone_end = (unsigned long)ptr + page_size(page);
496 
497         kasan_unpoison_shadow(ptr, size);
498         kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
499                 KASAN_PAGE_REDZONE);
500 
501         return (void *)ptr;
502 }
503 
504 void * __must_check kasan_krealloc(const void *object, size_t size, gfp_t flags)
505 {
506         struct page *page;
507 
508         if (unlikely(object == ZERO_SIZE_PTR))
509                 return (void *)object;
510 
511         page = virt_to_head_page(object);
512 
513         if (unlikely(!PageSlab(page)))
514                 return kasan_kmalloc_large(object, size, flags);
515         else
516                 return __kasan_kmalloc(page->slab_cache, object, size,
517                                                 flags, true);
518 }
519 
520 void kasan_poison_kfree(void *ptr, unsigned long ip)
521 {
522         struct page *page;
523 
524         page = virt_to_head_page(ptr);
525 
526         if (unlikely(!PageSlab(page))) {
527                 if (ptr != page_address(page)) {
528                         kasan_report_invalid_free(ptr, ip);
529                         return;
530                 }
531                 kasan_poison_shadow(ptr, page_size(page), KASAN_FREE_PAGE);
532         } else {
533                 __kasan_slab_free(page->slab_cache, ptr, ip, false);
534         }
535 }
536 
537 void kasan_kfree_large(void *ptr, unsigned long ip)
538 {
539         if (ptr != page_address(virt_to_head_page(ptr)))
540                 kasan_report_invalid_free(ptr, ip);
541         /* The object will be poisoned by page_alloc. */
542 }
543 
544 #ifndef CONFIG_KASAN_VMALLOC
545 int kasan_module_alloc(void *addr, size_t size)
546 {
547         void *ret;
548         size_t scaled_size;
549         size_t shadow_size;
550         unsigned long shadow_start;
551 
552         shadow_start = (unsigned long)kasan_mem_to_shadow(addr);
553         scaled_size = (size + KASAN_SHADOW_MASK) >> KASAN_SHADOW_SCALE_SHIFT;
554         shadow_size = round_up(scaled_size, PAGE_SIZE);
555 
556         if (WARN_ON(!PAGE_ALIGNED(shadow_start)))
557                 return -EINVAL;
558 
559         ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
560                         shadow_start + shadow_size,
561                         GFP_KERNEL,
562                         PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
563                         __builtin_return_address(0));
564 
565         if (ret) {
566                 __memset(ret, KASAN_SHADOW_INIT, shadow_size);
567                 find_vm_area(addr)->flags |= VM_KASAN;
568                 kmemleak_ignore(ret);
569                 return 0;
570         }
571 
572         return -ENOMEM;
573 }
574 
575 void kasan_free_shadow(const struct vm_struct *vm)
576 {
577         if (vm->flags & VM_KASAN)
578                 vfree(kasan_mem_to_shadow(vm->addr));
579 }
580 #endif
581 
582 #ifdef CONFIG_MEMORY_HOTPLUG
583 static bool shadow_mapped(unsigned long addr)
584 {
585         pgd_t *pgd = pgd_offset_k(addr);
586         p4d_t *p4d;
587         pud_t *pud;
588         pmd_t *pmd;
589         pte_t *pte;
590 
591         if (pgd_none(*pgd))
592                 return false;
593         p4d = p4d_offset(pgd, addr);
594         if (p4d_none(*p4d))
595                 return false;
596         pud = pud_offset(p4d, addr);
597         if (pud_none(*pud))
598                 return false;
599 
600         /*
601          * We can't use pud_large() or pud_huge(), the first one is
602          * arch-specific, the last one depends on HUGETLB_PAGE.  So let's abuse
603          * pud_bad(), if pud is bad then it's bad because it's huge.
604          */
605         if (pud_bad(*pud))
606                 return true;
607         pmd = pmd_offset(pud, addr);
608         if (pmd_none(*pmd))
609                 return false;
610 
611         if (pmd_bad(*pmd))
612                 return true;
613         pte = pte_offset_kernel(pmd, addr);
614         return !pte_none(*pte);
615 }
616 
617 static int __meminit kasan_mem_notifier(struct notifier_block *nb,
618                         unsigned long action, void *data)
619 {
620         struct memory_notify *mem_data = data;
621         unsigned long nr_shadow_pages, start_kaddr, shadow_start;
622         unsigned long shadow_end, shadow_size;
623 
624         nr_shadow_pages = mem_data->nr_pages >> KASAN_SHADOW_SCALE_SHIFT;
625         start_kaddr = (unsigned long)pfn_to_kaddr(mem_data->start_pfn);
626         shadow_start = (unsigned long)kasan_mem_to_shadow((void *)start_kaddr);
627         shadow_size = nr_shadow_pages << PAGE_SHIFT;
628         shadow_end = shadow_start + shadow_size;
629 
630         if (WARN_ON(mem_data->nr_pages % KASAN_SHADOW_SCALE_SIZE) ||
631                 WARN_ON(start_kaddr % (KASAN_SHADOW_SCALE_SIZE << PAGE_SHIFT)))
632                 return NOTIFY_BAD;
633 
634         switch (action) {
635         case MEM_GOING_ONLINE: {
636                 void *ret;
637 
638                 /*
639                  * If shadow is mapped already than it must have been mapped
640                  * during the boot. This could happen if we onlining previously
641                  * offlined memory.
642                  */
643                 if (shadow_mapped(shadow_start))
644                         return NOTIFY_OK;
645 
646                 ret = __vmalloc_node_range(shadow_size, PAGE_SIZE, shadow_start,
647                                         shadow_end, GFP_KERNEL,
648                                         PAGE_KERNEL, VM_NO_GUARD,
649                                         pfn_to_nid(mem_data->start_pfn),
650                                         __builtin_return_address(0));
651                 if (!ret)
652                         return NOTIFY_BAD;
653 
654                 kmemleak_ignore(ret);
655                 return NOTIFY_OK;
656         }
657         case MEM_CANCEL_ONLINE:
658         case MEM_OFFLINE: {
659                 struct vm_struct *vm;
660 
661                 /*
662                  * shadow_start was either mapped during boot by kasan_init()
663                  * or during memory online by __vmalloc_node_range().
664                  * In the latter case we can use vfree() to free shadow.
665                  * Non-NULL result of the find_vm_area() will tell us if
666                  * that was the second case.
667                  *
668                  * Currently it's not possible to free shadow mapped
669                  * during boot by kasan_init(). It's because the code
670                  * to do that hasn't been written yet. So we'll just
671                  * leak the memory.
672                  */
673                 vm = find_vm_area((void *)shadow_start);
674                 if (vm)
675                         vfree((void *)shadow_start);
676         }
677         }
678 
679         return NOTIFY_OK;
680 }
681 
682 static int __init kasan_memhotplug_init(void)
683 {
684         hotplug_memory_notifier(kasan_mem_notifier, 0);
685 
686         return 0;
687 }
688 
689 core_initcall(kasan_memhotplug_init);
690 #endif
691 
692 #ifdef CONFIG_KASAN_VMALLOC
693 static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
694                                       void *unused)
695 {
696         unsigned long page;
697         pte_t pte;
698 
699         if (likely(!pte_none(*ptep)))
700                 return 0;
701 
702         page = __get_free_page(GFP_KERNEL);
703         if (!page)
704                 return -ENOMEM;
705 
706         memset((void *)page, KASAN_VMALLOC_INVALID, PAGE_SIZE);
707         pte = pfn_pte(PFN_DOWN(__pa(page)), PAGE_KERNEL);
708 
709         spin_lock(&init_mm.page_table_lock);
710         if (likely(pte_none(*ptep))) {
711                 set_pte_at(&init_mm, addr, ptep, pte);
712                 page = 0;
713         }
714         spin_unlock(&init_mm.page_table_lock);
715         if (page)
716                 free_page(page);
717         return 0;
718 }
719 
720 int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
721 {
722         unsigned long shadow_start, shadow_end;
723         int ret;
724 
725         if (!is_vmalloc_or_module_addr((void *)addr))
726                 return 0;
727 
728         shadow_start = (unsigned long)kasan_mem_to_shadow((void *)addr);
729         shadow_start = ALIGN_DOWN(shadow_start, PAGE_SIZE);
730         shadow_end = (unsigned long)kasan_mem_to_shadow((void *)addr + size);
731         shadow_end = ALIGN(shadow_end, PAGE_SIZE);
732 
733         ret = apply_to_page_range(&init_mm, shadow_start,
734                                   shadow_end - shadow_start,
735                                   kasan_populate_vmalloc_pte, NULL);
736         if (ret)
737                 return ret;
738 
739         flush_cache_vmap(shadow_start, shadow_end);
740 
741         /*
742          * We need to be careful about inter-cpu effects here. Consider:
743          *
744          *   CPU#0                                CPU#1
745          * WRITE_ONCE(p, vmalloc(100));         while (x = READ_ONCE(p)) ;
746          *                                      p[99] = 1;
747          *
748          * With compiler instrumentation, that ends up looking like this:
749          *
750          *   CPU#0                                CPU#1
751          * // vmalloc() allocates memory
752          * // let a = area->addr
753          * // we reach kasan_populate_vmalloc
754          * // and call kasan_unpoison_shadow:
755          * STORE shadow(a), unpoison_val
756          * ...
757          * STORE shadow(a+99), unpoison_val     x = LOAD p
758          * // rest of vmalloc process           <data dependency>
759          * STORE p, a                           LOAD shadow(x+99)
760          *
761          * If there is no barrier between the end of unpoisioning the shadow
762          * and the store of the result to p, the stores could be committed
763          * in a different order by CPU#0, and CPU#1 could erroneously observe
764          * poison in the shadow.
765          *
766          * We need some sort of barrier between the stores.
767          *
768          * In the vmalloc() case, this is provided by a smp_wmb() in
769          * clear_vm_uninitialized_flag(). In the per-cpu allocator and in
770          * get_vm_area() and friends, the caller gets shadow allocated but
771          * doesn't have any pages mapped into the virtual address space that
772          * has been reserved. Mapping those pages in will involve taking and
773          * releasing a page-table lock, which will provide the barrier.
774          */
775 
776         return 0;
777 }
778 
779 /*
780  * Poison the shadow for a vmalloc region. Called as part of the
781  * freeing process at the time the region is freed.
782  */
783 void kasan_poison_vmalloc(const void *start, unsigned long size)
784 {
785         if (!is_vmalloc_or_module_addr(start))
786                 return;
787 
788         size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
789         kasan_poison_shadow(start, size, KASAN_VMALLOC_INVALID);
790 }
791 
792 void kasan_unpoison_vmalloc(const void *start, unsigned long size)
793 {
794         if (!is_vmalloc_or_module_addr(start))
795                 return;
796 
797         kasan_unpoison_shadow(start, size);
798 }
799 
800 static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
801                                         void *unused)
802 {
803         unsigned long page;
804 
805         page = (unsigned long)__va(pte_pfn(*ptep) << PAGE_SHIFT);
806 
807         spin_lock(&init_mm.page_table_lock);
808 
809         if (likely(!pte_none(*ptep))) {
810                 pte_clear(&init_mm, addr, ptep);
811                 free_page(page);
812         }
813         spin_unlock(&init_mm.page_table_lock);
814 
815         return 0;
816 }
817 
818 /*
819  * Release the backing for the vmalloc region [start, end), which
820  * lies within the free region [free_region_start, free_region_end).
821  *
822  * This can be run lazily, long after the region was freed. It runs
823  * under vmap_area_lock, so it's not safe to interact with the vmalloc/vmap
824  * infrastructure.
825  *
826  * How does this work?
827  * -------------------
828  *
829  * We have a region that is page aligned, labelled as A.
830  * That might not map onto the shadow in a way that is page-aligned:
831  *
832  *                    start                     end
833  *                    v                         v
834  * |????????|????????|AAAAAAAA|AA....AA|AAAAAAAA|????????| < vmalloc
835  *  -------- -------- --------          -------- --------
836  *      |        |       |                 |        |
837  *      |        |       |         /-------/        |
838  *      \-------\|/------/         |/---------------/
839  *              |||                ||
840  *             |??AAAAAA|AAAAAAAA|AA??????|                < shadow
841  *                 (1)      (2)      (3)
842  *
843  * First we align the start upwards and the end downwards, so that the
844  * shadow of the region aligns with shadow page boundaries. In the
845  * example, this gives us the shadow page (2). This is the shadow entirely
846  * covered by this allocation.
847  *
848  * Then we have the tricky bits. We want to know if we can free the
849  * partially covered shadow pages - (1) and (3) in the example. For this,
850  * we are given the start and end of the free region that contains this
851  * allocation. Extending our previous example, we could have:
852  *
853  *  free_region_start                                    free_region_end
854  *  |                 start                     end      |
855  *  v                 v                         v        v
856  * |FFFFFFFF|FFFFFFFF|AAAAAAAA|AA....AA|AAAAAAAA|FFFFFFFF| < vmalloc
857  *  -------- -------- --------          -------- --------
858  *      |        |       |                 |        |
859  *      |        |       |         /-------/        |
860  *      \-------\|/------/         |/---------------/
861  *              |||                ||
862  *             |FFAAAAAA|AAAAAAAA|AAF?????|                < shadow
863  *                 (1)      (2)      (3)
864  *
865  * Once again, we align the start of the free region up, and the end of
866  * the free region down so that the shadow is page aligned. So we can free
867  * page (1) - we know no allocation currently uses anything in that page,
868  * because all of it is in the vmalloc free region. But we cannot free
869  * page (3), because we can't be sure that the rest of it is unused.
870  *
871  * We only consider pages that contain part of the original region for
872  * freeing: we don't try to free other pages from the free region or we'd
873  * end up trying to free huge chunks of virtual address space.
874  *
875  * Concurrency
876  * -----------
877  *
878  * How do we know that we're not freeing a page that is simultaneously
879  * being used for a fresh allocation in kasan_populate_vmalloc(_pte)?
880  *
881  * We _can_ have kasan_release_vmalloc and kasan_populate_vmalloc running
882  * at the same time. While we run under free_vmap_area_lock, the population
883  * code does not.
884  *
885  * free_vmap_area_lock instead operates to ensure that the larger range
886  * [free_region_start, free_region_end) is safe: because __alloc_vmap_area and
887  * the per-cpu region-finding algorithm both run under free_vmap_area_lock,
888  * no space identified as free will become used while we are running. This
889  * means that so long as we are careful with alignment and only free shadow
890  * pages entirely covered by the free region, we will not run in to any
891  * trouble - any simultaneous allocations will be for disjoint regions.
892  */
893 void kasan_release_vmalloc(unsigned long start, unsigned long end,
894                            unsigned long free_region_start,
895                            unsigned long free_region_end)
896 {
897         void *shadow_start, *shadow_end;
898         unsigned long region_start, region_end;
899         unsigned long size;
900 
901         region_start = ALIGN(start, PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
902         region_end = ALIGN_DOWN(end, PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
903 
904         free_region_start = ALIGN(free_region_start,
905                                   PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
906 
907         if (start != region_start &&
908             free_region_start < region_start)
909                 region_start -= PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE;
910 
911         free_region_end = ALIGN_DOWN(free_region_end,
912                                      PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE);
913 
914         if (end != region_end &&
915             free_region_end > region_end)
916                 region_end += PAGE_SIZE * KASAN_SHADOW_SCALE_SIZE;
917 
918         shadow_start = kasan_mem_to_shadow((void *)region_start);
919         shadow_end = kasan_mem_to_shadow((void *)region_end);
920 
921         if (shadow_end > shadow_start) {
922                 size = shadow_end - shadow_start;
923                 apply_to_existing_page_range(&init_mm,
924                                              (unsigned long)shadow_start,
925                                              size, kasan_depopulate_vmalloc_pte,
926                                              NULL);
927                 flush_tlb_kernel_range((unsigned long)shadow_start,
928                                        (unsigned long)shadow_end);
929         }
930 }
931 #endif
932 

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