shadow.c 15 KB

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  1. // SPDX-License-Identifier: GPL-2.0
  2. /*
  3. * This file contains KASAN runtime code that manages shadow memory for
  4. * generic and software tag-based KASAN modes.
  5. *
  6. * Copyright (c) 2014 Samsung Electronics Co., Ltd.
  7. * Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
  8. *
  9. * Some code borrowed from https://github.com/xairy/kasan-prototype by
  10. * Andrey Konovalov <andreyknvl@gmail.com>
  11. */
  12. #include <linux/init.h>
  13. #include <linux/kasan.h>
  14. #include <linux/kernel.h>
  15. #include <linux/kfence.h>
  16. #include <linux/kmemleak.h>
  17. #include <linux/memory.h>
  18. #include <linux/mm.h>
  19. #include <linux/string.h>
  20. #include <linux/types.h>
  21. #include <linux/vmalloc.h>
  22. #include <asm/cacheflush.h>
  23. #include <asm/tlbflush.h>
  24. #include "kasan.h"
  25. bool __kasan_check_read(const volatile void *p, unsigned int size)
  26. {
  27. return kasan_check_range((unsigned long)p, size, false, _RET_IP_);
  28. }
  29. EXPORT_SYMBOL(__kasan_check_read);
  30. bool __kasan_check_write(const volatile void *p, unsigned int size)
  31. {
  32. return kasan_check_range((unsigned long)p, size, true, _RET_IP_);
  33. }
  34. EXPORT_SYMBOL(__kasan_check_write);
  35. #undef memset
  36. void *memset(void *addr, int c, size_t len)
  37. {
  38. if (!kasan_check_range((unsigned long)addr, len, true, _RET_IP_))
  39. return NULL;
  40. return __memset(addr, c, len);
  41. }
  42. #ifdef __HAVE_ARCH_MEMMOVE
  43. #undef memmove
  44. void *memmove(void *dest, const void *src, size_t len)
  45. {
  46. if (!kasan_check_range((unsigned long)src, len, false, _RET_IP_) ||
  47. !kasan_check_range((unsigned long)dest, len, true, _RET_IP_))
  48. return NULL;
  49. return __memmove(dest, src, len);
  50. }
  51. #endif
  52. #undef memcpy
  53. void *memcpy(void *dest, const void *src, size_t len)
  54. {
  55. if (!kasan_check_range((unsigned long)src, len, false, _RET_IP_) ||
  56. !kasan_check_range((unsigned long)dest, len, true, _RET_IP_))
  57. return NULL;
  58. return __memcpy(dest, src, len);
  59. }
  60. void kasan_poison(const void *addr, size_t size, u8 value, bool init)
  61. {
  62. void *shadow_start, *shadow_end;
  63. /*
  64. * Perform shadow offset calculation based on untagged address, as
  65. * some of the callers (e.g. kasan_poison_object_data) pass tagged
  66. * addresses to this function.
  67. */
  68. addr = kasan_reset_tag(addr);
  69. /* Skip KFENCE memory if called explicitly outside of sl*b. */
  70. if (is_kfence_address(addr))
  71. return;
  72. if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
  73. return;
  74. if (WARN_ON(size & KASAN_GRANULE_MASK))
  75. return;
  76. shadow_start = kasan_mem_to_shadow(addr);
  77. shadow_end = kasan_mem_to_shadow(addr + size);
  78. __memset(shadow_start, value, shadow_end - shadow_start);
  79. }
  80. EXPORT_SYMBOL(kasan_poison);
  81. #ifdef CONFIG_KASAN_GENERIC
  82. void kasan_poison_last_granule(const void *addr, size_t size)
  83. {
  84. if (size & KASAN_GRANULE_MASK) {
  85. u8 *shadow = (u8 *)kasan_mem_to_shadow(addr + size);
  86. *shadow = size & KASAN_GRANULE_MASK;
  87. }
  88. }
  89. #endif
  90. void kasan_unpoison(const void *addr, size_t size, bool init)
  91. {
  92. u8 tag = get_tag(addr);
  93. /*
  94. * Perform shadow offset calculation based on untagged address, as
  95. * some of the callers (e.g. kasan_unpoison_object_data) pass tagged
  96. * addresses to this function.
  97. */
  98. addr = kasan_reset_tag(addr);
  99. /*
  100. * Skip KFENCE memory if called explicitly outside of sl*b. Also note
  101. * that calls to ksize(), where size is not a multiple of machine-word
  102. * size, would otherwise poison the invalid portion of the word.
  103. */
  104. if (is_kfence_address(addr))
  105. return;
  106. if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
  107. return;
  108. /* Unpoison all granules that cover the object. */
  109. kasan_poison(addr, round_up(size, KASAN_GRANULE_SIZE), tag, false);
  110. /* Partially poison the last granule for the generic mode. */
  111. if (IS_ENABLED(CONFIG_KASAN_GENERIC))
  112. kasan_poison_last_granule(addr, size);
  113. }
  114. #ifdef CONFIG_MEMORY_HOTPLUG
  115. static bool shadow_mapped(unsigned long addr)
  116. {
  117. pgd_t *pgd = pgd_offset_k(addr);
  118. p4d_t *p4d;
  119. pud_t *pud;
  120. pmd_t *pmd;
  121. pte_t *pte;
  122. if (pgd_none(*pgd))
  123. return false;
  124. p4d = p4d_offset(pgd, addr);
  125. if (p4d_none(*p4d))
  126. return false;
  127. pud = pud_offset(p4d, addr);
  128. if (pud_none(*pud))
  129. return false;
  130. /*
  131. * We can't use pud_large() or pud_huge(), the first one is
  132. * arch-specific, the last one depends on HUGETLB_PAGE. So let's abuse
  133. * pud_bad(), if pud is bad then it's bad because it's huge.
  134. */
  135. if (pud_bad(*pud))
  136. return true;
  137. pmd = pmd_offset(pud, addr);
  138. if (pmd_none(*pmd))
  139. return false;
  140. if (pmd_bad(*pmd))
  141. return true;
  142. pte = pte_offset_kernel(pmd, addr);
  143. return !pte_none(*pte);
  144. }
  145. static int __meminit kasan_mem_notifier(struct notifier_block *nb,
  146. unsigned long action, void *data)
  147. {
  148. struct memory_notify *mem_data = data;
  149. unsigned long nr_shadow_pages, start_kaddr, shadow_start;
  150. unsigned long shadow_end, shadow_size;
  151. nr_shadow_pages = mem_data->nr_pages >> KASAN_SHADOW_SCALE_SHIFT;
  152. start_kaddr = (unsigned long)pfn_to_kaddr(mem_data->start_pfn);
  153. shadow_start = (unsigned long)kasan_mem_to_shadow((void *)start_kaddr);
  154. shadow_size = nr_shadow_pages << PAGE_SHIFT;
  155. shadow_end = shadow_start + shadow_size;
  156. if (WARN_ON(mem_data->nr_pages % KASAN_GRANULE_SIZE) ||
  157. WARN_ON(start_kaddr % KASAN_MEMORY_PER_SHADOW_PAGE))
  158. return NOTIFY_BAD;
  159. switch (action) {
  160. case MEM_GOING_ONLINE: {
  161. void *ret;
  162. /*
  163. * If shadow is mapped already than it must have been mapped
  164. * during the boot. This could happen if we onlining previously
  165. * offlined memory.
  166. */
  167. if (shadow_mapped(shadow_start))
  168. return NOTIFY_OK;
  169. ret = __vmalloc_node_range(shadow_size, PAGE_SIZE, shadow_start,
  170. shadow_end, GFP_KERNEL,
  171. PAGE_KERNEL, VM_NO_GUARD,
  172. pfn_to_nid(mem_data->start_pfn),
  173. __builtin_return_address(0));
  174. if (!ret)
  175. return NOTIFY_BAD;
  176. kmemleak_ignore(ret);
  177. return NOTIFY_OK;
  178. }
  179. case MEM_CANCEL_ONLINE:
  180. case MEM_OFFLINE: {
  181. struct vm_struct *vm;
  182. /*
  183. * shadow_start was either mapped during boot by kasan_init()
  184. * or during memory online by __vmalloc_node_range().
  185. * In the latter case we can use vfree() to free shadow.
  186. * Non-NULL result of the find_vm_area() will tell us if
  187. * that was the second case.
  188. *
  189. * Currently it's not possible to free shadow mapped
  190. * during boot by kasan_init(). It's because the code
  191. * to do that hasn't been written yet. So we'll just
  192. * leak the memory.
  193. */
  194. vm = find_vm_area((void *)shadow_start);
  195. if (vm)
  196. vfree((void *)shadow_start);
  197. }
  198. }
  199. return NOTIFY_OK;
  200. }
  201. static int __init kasan_memhotplug_init(void)
  202. {
  203. hotplug_memory_notifier(kasan_mem_notifier, 0);
  204. return 0;
  205. }
  206. core_initcall(kasan_memhotplug_init);
  207. #endif
  208. #ifdef CONFIG_KASAN_VMALLOC
  209. static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
  210. void *unused)
  211. {
  212. unsigned long page;
  213. pte_t pte;
  214. if (likely(!pte_none(*ptep)))
  215. return 0;
  216. page = __get_free_page(GFP_KERNEL);
  217. if (!page)
  218. return -ENOMEM;
  219. memset((void *)page, KASAN_VMALLOC_INVALID, PAGE_SIZE);
  220. pte = pfn_pte(PFN_DOWN(__pa(page)), PAGE_KERNEL);
  221. spin_lock(&init_mm.page_table_lock);
  222. if (likely(pte_none(*ptep))) {
  223. set_pte_at(&init_mm, addr, ptep, pte);
  224. page = 0;
  225. }
  226. spin_unlock(&init_mm.page_table_lock);
  227. if (page)
  228. free_page(page);
  229. return 0;
  230. }
  231. int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
  232. {
  233. unsigned long shadow_start, shadow_end;
  234. int ret;
  235. if (!is_vmalloc_or_module_addr((void *)addr))
  236. return 0;
  237. shadow_start = (unsigned long)kasan_mem_to_shadow((void *)addr);
  238. shadow_start = ALIGN_DOWN(shadow_start, PAGE_SIZE);
  239. shadow_end = (unsigned long)kasan_mem_to_shadow((void *)addr + size);
  240. shadow_end = ALIGN(shadow_end, PAGE_SIZE);
  241. ret = apply_to_page_range(&init_mm, shadow_start,
  242. shadow_end - shadow_start,
  243. kasan_populate_vmalloc_pte, NULL);
  244. if (ret)
  245. return ret;
  246. flush_cache_vmap(shadow_start, shadow_end);
  247. /*
  248. * We need to be careful about inter-cpu effects here. Consider:
  249. *
  250. * CPU#0 CPU#1
  251. * WRITE_ONCE(p, vmalloc(100)); while (x = READ_ONCE(p)) ;
  252. * p[99] = 1;
  253. *
  254. * With compiler instrumentation, that ends up looking like this:
  255. *
  256. * CPU#0 CPU#1
  257. * // vmalloc() allocates memory
  258. * // let a = area->addr
  259. * // we reach kasan_populate_vmalloc
  260. * // and call kasan_unpoison:
  261. * STORE shadow(a), unpoison_val
  262. * ...
  263. * STORE shadow(a+99), unpoison_val x = LOAD p
  264. * // rest of vmalloc process <data dependency>
  265. * STORE p, a LOAD shadow(x+99)
  266. *
  267. * If there is no barrier between the end of unpoisioning the shadow
  268. * and the store of the result to p, the stores could be committed
  269. * in a different order by CPU#0, and CPU#1 could erroneously observe
  270. * poison in the shadow.
  271. *
  272. * We need some sort of barrier between the stores.
  273. *
  274. * In the vmalloc() case, this is provided by a smp_wmb() in
  275. * clear_vm_uninitialized_flag(). In the per-cpu allocator and in
  276. * get_vm_area() and friends, the caller gets shadow allocated but
  277. * doesn't have any pages mapped into the virtual address space that
  278. * has been reserved. Mapping those pages in will involve taking and
  279. * releasing a page-table lock, which will provide the barrier.
  280. */
  281. return 0;
  282. }
  283. /*
  284. * Poison the shadow for a vmalloc region. Called as part of the
  285. * freeing process at the time the region is freed.
  286. */
  287. void kasan_poison_vmalloc(const void *start, unsigned long size)
  288. {
  289. if (!is_vmalloc_or_module_addr(start))
  290. return;
  291. size = round_up(size, KASAN_GRANULE_SIZE);
  292. kasan_poison(start, size, KASAN_VMALLOC_INVALID, false);
  293. }
  294. void kasan_unpoison_vmalloc(const void *start, unsigned long size)
  295. {
  296. if (!is_vmalloc_or_module_addr(start))
  297. return;
  298. kasan_unpoison(start, size, false);
  299. }
  300. static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
  301. void *unused)
  302. {
  303. unsigned long page;
  304. page = (unsigned long)__va(pte_pfn(*ptep) << PAGE_SHIFT);
  305. spin_lock(&init_mm.page_table_lock);
  306. if (likely(!pte_none(*ptep))) {
  307. pte_clear(&init_mm, addr, ptep);
  308. free_page(page);
  309. }
  310. spin_unlock(&init_mm.page_table_lock);
  311. return 0;
  312. }
  313. /*
  314. * Release the backing for the vmalloc region [start, end), which
  315. * lies within the free region [free_region_start, free_region_end).
  316. *
  317. * This can be run lazily, long after the region was freed. It runs
  318. * under vmap_area_lock, so it's not safe to interact with the vmalloc/vmap
  319. * infrastructure.
  320. *
  321. * How does this work?
  322. * -------------------
  323. *
  324. * We have a region that is page aligned, labelled as A.
  325. * That might not map onto the shadow in a way that is page-aligned:
  326. *
  327. * start end
  328. * v v
  329. * |????????|????????|AAAAAAAA|AA....AA|AAAAAAAA|????????| < vmalloc
  330. * -------- -------- -------- -------- --------
  331. * | | | | |
  332. * | | | /-------/ |
  333. * \-------\|/------/ |/---------------/
  334. * ||| ||
  335. * |??AAAAAA|AAAAAAAA|AA??????| < shadow
  336. * (1) (2) (3)
  337. *
  338. * First we align the start upwards and the end downwards, so that the
  339. * shadow of the region aligns with shadow page boundaries. In the
  340. * example, this gives us the shadow page (2). This is the shadow entirely
  341. * covered by this allocation.
  342. *
  343. * Then we have the tricky bits. We want to know if we can free the
  344. * partially covered shadow pages - (1) and (3) in the example. For this,
  345. * we are given the start and end of the free region that contains this
  346. * allocation. Extending our previous example, we could have:
  347. *
  348. * free_region_start free_region_end
  349. * | start end |
  350. * v v v v
  351. * |FFFFFFFF|FFFFFFFF|AAAAAAAA|AA....AA|AAAAAAAA|FFFFFFFF| < vmalloc
  352. * -------- -------- -------- -------- --------
  353. * | | | | |
  354. * | | | /-------/ |
  355. * \-------\|/------/ |/---------------/
  356. * ||| ||
  357. * |FFAAAAAA|AAAAAAAA|AAF?????| < shadow
  358. * (1) (2) (3)
  359. *
  360. * Once again, we align the start of the free region up, and the end of
  361. * the free region down so that the shadow is page aligned. So we can free
  362. * page (1) - we know no allocation currently uses anything in that page,
  363. * because all of it is in the vmalloc free region. But we cannot free
  364. * page (3), because we can't be sure that the rest of it is unused.
  365. *
  366. * We only consider pages that contain part of the original region for
  367. * freeing: we don't try to free other pages from the free region or we'd
  368. * end up trying to free huge chunks of virtual address space.
  369. *
  370. * Concurrency
  371. * -----------
  372. *
  373. * How do we know that we're not freeing a page that is simultaneously
  374. * being used for a fresh allocation in kasan_populate_vmalloc(_pte)?
  375. *
  376. * We _can_ have kasan_release_vmalloc and kasan_populate_vmalloc running
  377. * at the same time. While we run under free_vmap_area_lock, the population
  378. * code does not.
  379. *
  380. * free_vmap_area_lock instead operates to ensure that the larger range
  381. * [free_region_start, free_region_end) is safe: because __alloc_vmap_area and
  382. * the per-cpu region-finding algorithm both run under free_vmap_area_lock,
  383. * no space identified as free will become used while we are running. This
  384. * means that so long as we are careful with alignment and only free shadow
  385. * pages entirely covered by the free region, we will not run in to any
  386. * trouble - any simultaneous allocations will be for disjoint regions.
  387. */
  388. void kasan_release_vmalloc(unsigned long start, unsigned long end,
  389. unsigned long free_region_start,
  390. unsigned long free_region_end)
  391. {
  392. void *shadow_start, *shadow_end;
  393. unsigned long region_start, region_end;
  394. unsigned long size;
  395. region_start = ALIGN(start, KASAN_MEMORY_PER_SHADOW_PAGE);
  396. region_end = ALIGN_DOWN(end, KASAN_MEMORY_PER_SHADOW_PAGE);
  397. free_region_start = ALIGN(free_region_start, KASAN_MEMORY_PER_SHADOW_PAGE);
  398. if (start != region_start &&
  399. free_region_start < region_start)
  400. region_start -= KASAN_MEMORY_PER_SHADOW_PAGE;
  401. free_region_end = ALIGN_DOWN(free_region_end, KASAN_MEMORY_PER_SHADOW_PAGE);
  402. if (end != region_end &&
  403. free_region_end > region_end)
  404. region_end += KASAN_MEMORY_PER_SHADOW_PAGE;
  405. shadow_start = kasan_mem_to_shadow((void *)region_start);
  406. shadow_end = kasan_mem_to_shadow((void *)region_end);
  407. if (shadow_end > shadow_start) {
  408. size = shadow_end - shadow_start;
  409. apply_to_existing_page_range(&init_mm,
  410. (unsigned long)shadow_start,
  411. size, kasan_depopulate_vmalloc_pte,
  412. NULL);
  413. flush_tlb_kernel_range((unsigned long)shadow_start,
  414. (unsigned long)shadow_end);
  415. }
  416. }
  417. #else /* CONFIG_KASAN_VMALLOC */
  418. int kasan_module_alloc(void *addr, size_t size)
  419. {
  420. void *ret;
  421. size_t scaled_size;
  422. size_t shadow_size;
  423. unsigned long shadow_start;
  424. shadow_start = (unsigned long)kasan_mem_to_shadow(addr);
  425. scaled_size = (size + KASAN_GRANULE_SIZE - 1) >>
  426. KASAN_SHADOW_SCALE_SHIFT;
  427. shadow_size = round_up(scaled_size, PAGE_SIZE);
  428. if (WARN_ON(!PAGE_ALIGNED(shadow_start)))
  429. return -EINVAL;
  430. ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
  431. shadow_start + shadow_size,
  432. GFP_KERNEL,
  433. PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
  434. __builtin_return_address(0));
  435. if (ret) {
  436. __memset(ret, KASAN_SHADOW_INIT, shadow_size);
  437. find_vm_area(addr)->flags |= VM_KASAN;
  438. kmemleak_ignore(ret);
  439. return 0;
  440. }
  441. return -ENOMEM;
  442. }
  443. void kasan_free_shadow(const struct vm_struct *vm)
  444. {
  445. if (vm->flags & VM_KASAN)
  446. vfree(kasan_mem_to_shadow(vm->addr));
  447. }
  448. #endif