xref: /openbmc/linux/mm/kasan/common.c (revision 7ac3945d)
1  // SPDX-License-Identifier: GPL-2.0
2  /*
3   * This file contains common 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  
12  #include <linux/export.h>
13  #include <linux/init.h>
14  #include <linux/kasan.h>
15  #include <linux/kernel.h>
16  #include <linux/linkage.h>
17  #include <linux/memblock.h>
18  #include <linux/memory.h>
19  #include <linux/mm.h>
20  #include <linux/module.h>
21  #include <linux/printk.h>
22  #include <linux/sched.h>
23  #include <linux/sched/task_stack.h>
24  #include <linux/slab.h>
25  #include <linux/stacktrace.h>
26  #include <linux/string.h>
27  #include <linux/types.h>
28  #include <linux/bug.h>
29  
30  #include "kasan.h"
31  #include "../slab.h"
32  
33  depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
34  {
35  	unsigned long entries[KASAN_STACK_DEPTH];
36  	unsigned int nr_entries;
37  
38  	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
39  	return __stack_depot_save(entries, nr_entries, flags, can_alloc);
40  }
41  
42  void kasan_set_track(struct kasan_track *track, gfp_t flags)
43  {
44  	track->pid = current->pid;
45  	track->stack = kasan_save_stack(flags, true);
46  }
47  
48  #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
49  void kasan_enable_current(void)
50  {
51  	current->kasan_depth++;
52  }
53  EXPORT_SYMBOL(kasan_enable_current);
54  
55  void kasan_disable_current(void)
56  {
57  	current->kasan_depth--;
58  }
59  EXPORT_SYMBOL(kasan_disable_current);
60  
61  #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
62  
63  void __kasan_unpoison_range(const void *address, size_t size)
64  {
65  	kasan_unpoison(address, size, false);
66  }
67  
68  #ifdef CONFIG_KASAN_STACK
69  /* Unpoison the entire stack for a task. */
70  void kasan_unpoison_task_stack(struct task_struct *task)
71  {
72  	void *base = task_stack_page(task);
73  
74  	kasan_unpoison(base, THREAD_SIZE, false);
75  }
76  
77  /* Unpoison the stack for the current task beyond a watermark sp value. */
78  asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
79  {
80  	/*
81  	 * Calculate the task stack base address.  Avoid using 'current'
82  	 * because this function is called by early resume code which hasn't
83  	 * yet set up the percpu register (%gs).
84  	 */
85  	void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1));
86  
87  	kasan_unpoison(base, watermark - base, false);
88  }
89  #endif /* CONFIG_KASAN_STACK */
90  
91  /*
92   * Only allow cache merging when stack collection is disabled and no metadata
93   * is present.
94   */
95  slab_flags_t __kasan_never_merge(void)
96  {
97  	if (kasan_stack_collection_enabled())
98  		return SLAB_KASAN;
99  	return 0;
100  }
101  
102  void __kasan_unpoison_pages(struct page *page, unsigned int order, bool init)
103  {
104  	u8 tag;
105  	unsigned long i;
106  
107  	if (unlikely(PageHighMem(page)))
108  		return;
109  
110  	tag = kasan_random_tag();
111  	for (i = 0; i < (1 << order); i++)
112  		page_kasan_tag_set(page + i, tag);
113  	kasan_unpoison(page_address(page), PAGE_SIZE << order, init);
114  }
115  
116  void __kasan_poison_pages(struct page *page, unsigned int order, bool init)
117  {
118  	if (likely(!PageHighMem(page)))
119  		kasan_poison(page_address(page), PAGE_SIZE << order,
120  			     KASAN_PAGE_FREE, init);
121  }
122  
123  /*
124   * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
125   * For larger allocations larger redzones are used.
126   */
127  static inline unsigned int optimal_redzone(unsigned int object_size)
128  {
129  	return
130  		object_size <= 64        - 16   ? 16 :
131  		object_size <= 128       - 32   ? 32 :
132  		object_size <= 512       - 64   ? 64 :
133  		object_size <= 4096      - 128  ? 128 :
134  		object_size <= (1 << 14) - 256  ? 256 :
135  		object_size <= (1 << 15) - 512  ? 512 :
136  		object_size <= (1 << 16) - 1024 ? 1024 : 2048;
137  }
138  
139  void __kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
140  			  slab_flags_t *flags)
141  {
142  	unsigned int ok_size;
143  	unsigned int optimal_size;
144  
145  	/*
146  	 * SLAB_KASAN is used to mark caches as ones that are sanitized by
147  	 * KASAN. Currently this flag is used in two places:
148  	 * 1. In slab_ksize() when calculating the size of the accessible
149  	 *    memory within the object.
150  	 * 2. In slab_common.c to prevent merging of sanitized caches.
151  	 */
152  	*flags |= SLAB_KASAN;
153  
154  	if (!kasan_stack_collection_enabled())
155  		return;
156  
157  	ok_size = *size;
158  
159  	/* Add alloc meta into redzone. */
160  	cache->kasan_info.alloc_meta_offset = *size;
161  	*size += sizeof(struct kasan_alloc_meta);
162  
163  	/*
164  	 * If alloc meta doesn't fit, don't add it.
165  	 * This can only happen with SLAB, as it has KMALLOC_MAX_SIZE equal
166  	 * to KMALLOC_MAX_CACHE_SIZE and doesn't fall back to page_alloc for
167  	 * larger sizes.
168  	 */
169  	if (*size > KMALLOC_MAX_SIZE) {
170  		cache->kasan_info.alloc_meta_offset = 0;
171  		*size = ok_size;
172  		/* Continue, since free meta might still fit. */
173  	}
174  
175  	/* Only the generic mode uses free meta or flexible redzones. */
176  	if (!IS_ENABLED(CONFIG_KASAN_GENERIC)) {
177  		cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META;
178  		return;
179  	}
180  
181  	/*
182  	 * Add free meta into redzone when it's not possible to store
183  	 * it in the object. This is the case when:
184  	 * 1. Object is SLAB_TYPESAFE_BY_RCU, which means that it can
185  	 *    be touched after it was freed, or
186  	 * 2. Object has a constructor, which means it's expected to
187  	 *    retain its content until the next allocation, or
188  	 * 3. Object is too small.
189  	 * Otherwise cache->kasan_info.free_meta_offset = 0 is implied.
190  	 */
191  	if ((cache->flags & SLAB_TYPESAFE_BY_RCU) || cache->ctor ||
192  	    cache->object_size < sizeof(struct kasan_free_meta)) {
193  		ok_size = *size;
194  
195  		cache->kasan_info.free_meta_offset = *size;
196  		*size += sizeof(struct kasan_free_meta);
197  
198  		/* If free meta doesn't fit, don't add it. */
199  		if (*size > KMALLOC_MAX_SIZE) {
200  			cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META;
201  			*size = ok_size;
202  		}
203  	}
204  
205  	/* Calculate size with optimal redzone. */
206  	optimal_size = cache->object_size + optimal_redzone(cache->object_size);
207  	/* Limit it with KMALLOC_MAX_SIZE (relevant for SLAB only). */
208  	if (optimal_size > KMALLOC_MAX_SIZE)
209  		optimal_size = KMALLOC_MAX_SIZE;
210  	/* Use optimal size if the size with added metas is not large enough. */
211  	if (*size < optimal_size)
212  		*size = optimal_size;
213  }
214  
215  void __kasan_cache_create_kmalloc(struct kmem_cache *cache)
216  {
217  	cache->kasan_info.is_kmalloc = true;
218  }
219  
220  size_t __kasan_metadata_size(struct kmem_cache *cache)
221  {
222  	if (!kasan_stack_collection_enabled())
223  		return 0;
224  	return (cache->kasan_info.alloc_meta_offset ?
225  		sizeof(struct kasan_alloc_meta) : 0) +
226  		(cache->kasan_info.free_meta_offset ?
227  		sizeof(struct kasan_free_meta) : 0);
228  }
229  
230  struct kasan_alloc_meta *kasan_get_alloc_meta(struct kmem_cache *cache,
231  					      const void *object)
232  {
233  	if (!cache->kasan_info.alloc_meta_offset)
234  		return NULL;
235  	return kasan_reset_tag(object) + cache->kasan_info.alloc_meta_offset;
236  }
237  
238  #ifdef CONFIG_KASAN_GENERIC
239  struct kasan_free_meta *kasan_get_free_meta(struct kmem_cache *cache,
240  					    const void *object)
241  {
242  	BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
243  	if (cache->kasan_info.free_meta_offset == KASAN_NO_FREE_META)
244  		return NULL;
245  	return kasan_reset_tag(object) + cache->kasan_info.free_meta_offset;
246  }
247  #endif
248  
249  void __kasan_poison_slab(struct slab *slab)
250  {
251  	struct page *page = slab_page(slab);
252  	unsigned long i;
253  
254  	for (i = 0; i < compound_nr(page); i++)
255  		page_kasan_tag_reset(page + i);
256  	kasan_poison(page_address(page), page_size(page),
257  		     KASAN_SLAB_REDZONE, false);
258  }
259  
260  void __kasan_unpoison_object_data(struct kmem_cache *cache, void *object)
261  {
262  	kasan_unpoison(object, cache->object_size, false);
263  }
264  
265  void __kasan_poison_object_data(struct kmem_cache *cache, void *object)
266  {
267  	kasan_poison(object, round_up(cache->object_size, KASAN_GRANULE_SIZE),
268  			KASAN_SLAB_REDZONE, false);
269  }
270  
271  /*
272   * This function assigns a tag to an object considering the following:
273   * 1. A cache might have a constructor, which might save a pointer to a slab
274   *    object somewhere (e.g. in the object itself). We preassign a tag for
275   *    each object in caches with constructors during slab creation and reuse
276   *    the same tag each time a particular object is allocated.
277   * 2. A cache might be SLAB_TYPESAFE_BY_RCU, which means objects can be
278   *    accessed after being freed. We preassign tags for objects in these
279   *    caches as well.
280   * 3. For SLAB allocator we can't preassign tags randomly since the freelist
281   *    is stored as an array of indexes instead of a linked list. Assign tags
282   *    based on objects indexes, so that objects that are next to each other
283   *    get different tags.
284   */
285  static inline u8 assign_tag(struct kmem_cache *cache,
286  					const void *object, bool init)
287  {
288  	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
289  		return 0xff;
290  
291  	/*
292  	 * If the cache neither has a constructor nor has SLAB_TYPESAFE_BY_RCU
293  	 * set, assign a tag when the object is being allocated (init == false).
294  	 */
295  	if (!cache->ctor && !(cache->flags & SLAB_TYPESAFE_BY_RCU))
296  		return init ? KASAN_TAG_KERNEL : kasan_random_tag();
297  
298  	/* For caches that either have a constructor or SLAB_TYPESAFE_BY_RCU: */
299  #ifdef CONFIG_SLAB
300  	/* For SLAB assign tags based on the object index in the freelist. */
301  	return (u8)obj_to_index(cache, virt_to_slab(object), (void *)object);
302  #else
303  	/*
304  	 * For SLUB assign a random tag during slab creation, otherwise reuse
305  	 * the already assigned tag.
306  	 */
307  	return init ? kasan_random_tag() : get_tag(object);
308  #endif
309  }
310  
311  void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache,
312  						const void *object)
313  {
314  	struct kasan_alloc_meta *alloc_meta;
315  
316  	if (kasan_stack_collection_enabled()) {
317  		alloc_meta = kasan_get_alloc_meta(cache, object);
318  		if (alloc_meta)
319  			__memset(alloc_meta, 0, sizeof(*alloc_meta));
320  	}
321  
322  	/* Tag is ignored in set_tag() without CONFIG_KASAN_SW/HW_TAGS */
323  	object = set_tag(object, assign_tag(cache, object, true));
324  
325  	return (void *)object;
326  }
327  
328  static inline bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
329  				unsigned long ip, bool quarantine, bool init)
330  {
331  	u8 tag;
332  	void *tagged_object;
333  
334  	if (!kasan_arch_is_ready())
335  		return false;
336  
337  	tag = get_tag(object);
338  	tagged_object = object;
339  	object = kasan_reset_tag(object);
340  
341  	if (is_kfence_address(object))
342  		return false;
343  
344  	if (unlikely(nearest_obj(cache, virt_to_slab(object), object) !=
345  	    object)) {
346  		kasan_report_invalid_free(tagged_object, ip);
347  		return true;
348  	}
349  
350  	/* RCU slabs could be legally used after free within the RCU period */
351  	if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
352  		return false;
353  
354  	if (!kasan_byte_accessible(tagged_object)) {
355  		kasan_report_invalid_free(tagged_object, ip);
356  		return true;
357  	}
358  
359  	kasan_poison(object, round_up(cache->object_size, KASAN_GRANULE_SIZE),
360  			KASAN_SLAB_FREE, init);
361  
362  	if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine))
363  		return false;
364  
365  	if (kasan_stack_collection_enabled())
366  		kasan_set_free_info(cache, object, tag);
367  
368  	return kasan_quarantine_put(cache, object);
369  }
370  
371  bool __kasan_slab_free(struct kmem_cache *cache, void *object,
372  				unsigned long ip, bool init)
373  {
374  	return ____kasan_slab_free(cache, object, ip, true, init);
375  }
376  
377  static inline bool ____kasan_kfree_large(void *ptr, unsigned long ip)
378  {
379  	if (ptr != page_address(virt_to_head_page(ptr))) {
380  		kasan_report_invalid_free(ptr, ip);
381  		return true;
382  	}
383  
384  	if (!kasan_byte_accessible(ptr)) {
385  		kasan_report_invalid_free(ptr, ip);
386  		return true;
387  	}
388  
389  	/*
390  	 * The object will be poisoned by kasan_poison_pages() or
391  	 * kasan_slab_free_mempool().
392  	 */
393  
394  	return false;
395  }
396  
397  void __kasan_kfree_large(void *ptr, unsigned long ip)
398  {
399  	____kasan_kfree_large(ptr, ip);
400  }
401  
402  void __kasan_slab_free_mempool(void *ptr, unsigned long ip)
403  {
404  	struct folio *folio;
405  
406  	folio = virt_to_folio(ptr);
407  
408  	/*
409  	 * Even though this function is only called for kmem_cache_alloc and
410  	 * kmalloc backed mempool allocations, those allocations can still be
411  	 * !PageSlab() when the size provided to kmalloc is larger than
412  	 * KMALLOC_MAX_SIZE, and kmalloc falls back onto page_alloc.
413  	 */
414  	if (unlikely(!folio_test_slab(folio))) {
415  		if (____kasan_kfree_large(ptr, ip))
416  			return;
417  		kasan_poison(ptr, folio_size(folio), KASAN_PAGE_FREE, false);
418  	} else {
419  		struct slab *slab = folio_slab(folio);
420  
421  		____kasan_slab_free(slab->slab_cache, ptr, ip, false, false);
422  	}
423  }
424  
425  static void set_alloc_info(struct kmem_cache *cache, void *object,
426  				gfp_t flags, bool is_kmalloc)
427  {
428  	struct kasan_alloc_meta *alloc_meta;
429  
430  	/* Don't save alloc info for kmalloc caches in kasan_slab_alloc(). */
431  	if (cache->kasan_info.is_kmalloc && !is_kmalloc)
432  		return;
433  
434  	alloc_meta = kasan_get_alloc_meta(cache, object);
435  	if (alloc_meta)
436  		kasan_set_track(&alloc_meta->alloc_track, flags);
437  }
438  
439  void * __must_check __kasan_slab_alloc(struct kmem_cache *cache,
440  					void *object, gfp_t flags, bool init)
441  {
442  	u8 tag;
443  	void *tagged_object;
444  
445  	if (gfpflags_allow_blocking(flags))
446  		kasan_quarantine_reduce();
447  
448  	if (unlikely(object == NULL))
449  		return NULL;
450  
451  	if (is_kfence_address(object))
452  		return (void *)object;
453  
454  	/*
455  	 * Generate and assign random tag for tag-based modes.
456  	 * Tag is ignored in set_tag() for the generic mode.
457  	 */
458  	tag = assign_tag(cache, object, false);
459  	tagged_object = set_tag(object, tag);
460  
461  	/*
462  	 * Unpoison the whole object.
463  	 * For kmalloc() allocations, kasan_kmalloc() will do precise poisoning.
464  	 */
465  	kasan_unpoison(tagged_object, cache->object_size, init);
466  
467  	/* Save alloc info (if possible) for non-kmalloc() allocations. */
468  	if (kasan_stack_collection_enabled())
469  		set_alloc_info(cache, (void *)object, flags, false);
470  
471  	return tagged_object;
472  }
473  
474  static inline void *____kasan_kmalloc(struct kmem_cache *cache,
475  				const void *object, size_t size, gfp_t flags)
476  {
477  	unsigned long redzone_start;
478  	unsigned long redzone_end;
479  
480  	if (gfpflags_allow_blocking(flags))
481  		kasan_quarantine_reduce();
482  
483  	if (unlikely(object == NULL))
484  		return NULL;
485  
486  	if (is_kfence_address(kasan_reset_tag(object)))
487  		return (void *)object;
488  
489  	/*
490  	 * The object has already been unpoisoned by kasan_slab_alloc() for
491  	 * kmalloc() or by kasan_krealloc() for krealloc().
492  	 */
493  
494  	/*
495  	 * The redzone has byte-level precision for the generic mode.
496  	 * Partially poison the last object granule to cover the unaligned
497  	 * part of the redzone.
498  	 */
499  	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
500  		kasan_poison_last_granule((void *)object, size);
501  
502  	/* Poison the aligned part of the redzone. */
503  	redzone_start = round_up((unsigned long)(object + size),
504  				KASAN_GRANULE_SIZE);
505  	redzone_end = round_up((unsigned long)(object + cache->object_size),
506  				KASAN_GRANULE_SIZE);
507  	kasan_poison((void *)redzone_start, redzone_end - redzone_start,
508  			   KASAN_SLAB_REDZONE, false);
509  
510  	/*
511  	 * Save alloc info (if possible) for kmalloc() allocations.
512  	 * This also rewrites the alloc info when called from kasan_krealloc().
513  	 */
514  	if (kasan_stack_collection_enabled())
515  		set_alloc_info(cache, (void *)object, flags, true);
516  
517  	/* Keep the tag that was set by kasan_slab_alloc(). */
518  	return (void *)object;
519  }
520  
521  void * __must_check __kasan_kmalloc(struct kmem_cache *cache, const void *object,
522  					size_t size, gfp_t flags)
523  {
524  	return ____kasan_kmalloc(cache, object, size, flags);
525  }
526  EXPORT_SYMBOL(__kasan_kmalloc);
527  
528  void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
529  						gfp_t flags)
530  {
531  	unsigned long redzone_start;
532  	unsigned long redzone_end;
533  
534  	if (gfpflags_allow_blocking(flags))
535  		kasan_quarantine_reduce();
536  
537  	if (unlikely(ptr == NULL))
538  		return NULL;
539  
540  	/*
541  	 * The object has already been unpoisoned by kasan_unpoison_pages() for
542  	 * alloc_pages() or by kasan_krealloc() for krealloc().
543  	 */
544  
545  	/*
546  	 * The redzone has byte-level precision for the generic mode.
547  	 * Partially poison the last object granule to cover the unaligned
548  	 * part of the redzone.
549  	 */
550  	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
551  		kasan_poison_last_granule(ptr, size);
552  
553  	/* Poison the aligned part of the redzone. */
554  	redzone_start = round_up((unsigned long)(ptr + size),
555  				KASAN_GRANULE_SIZE);
556  	redzone_end = (unsigned long)ptr + page_size(virt_to_page(ptr));
557  	kasan_poison((void *)redzone_start, redzone_end - redzone_start,
558  		     KASAN_PAGE_REDZONE, false);
559  
560  	return (void *)ptr;
561  }
562  
563  void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flags)
564  {
565  	struct slab *slab;
566  
567  	if (unlikely(object == ZERO_SIZE_PTR))
568  		return (void *)object;
569  
570  	/*
571  	 * Unpoison the object's data.
572  	 * Part of it might already have been unpoisoned, but it's unknown
573  	 * how big that part is.
574  	 */
575  	kasan_unpoison(object, size, false);
576  
577  	slab = virt_to_slab(object);
578  
579  	/* Piggy-back on kmalloc() instrumentation to poison the redzone. */
580  	if (unlikely(!slab))
581  		return __kasan_kmalloc_large(object, size, flags);
582  	else
583  		return ____kasan_kmalloc(slab->slab_cache, object, size, flags);
584  }
585  
586  bool __kasan_check_byte(const void *address, unsigned long ip)
587  {
588  	if (!kasan_byte_accessible(address)) {
589  		kasan_report((unsigned long)address, 1, false, ip);
590  		return false;
591  	}
592  	return true;
593  }
594