1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Generic stack depot for storing stack traces.
4  *
5  * Some debugging tools need to save stack traces of certain events which can
6  * be later presented to the user. For example, KASAN needs to safe alloc and
7  * free stacks for each object, but storing two stack traces per object
8  * requires too much memory (e.g. SLUB_DEBUG needs 256 bytes per object for
9  * that).
10  *
11  * Instead, stack depot maintains a hashtable of unique stacktraces. Since alloc
12  * and free stacks repeat a lot, we save about 100x space.
13  * Stacks are never removed from depot, so we store them contiguously one after
14  * another in a contiguous memory allocation.
15  *
16  * Author: Alexander Potapenko <glider@google.com>
17  * Copyright (C) 2016 Google, Inc.
18  *
19  * Based on code by Dmitry Chernenkov.
20  */
21 
22 #include <linux/gfp.h>
23 #include <linux/jhash.h>
24 #include <linux/kernel.h>
25 #include <linux/mm.h>
26 #include <linux/mutex.h>
27 #include <linux/percpu.h>
28 #include <linux/printk.h>
29 #include <linux/slab.h>
30 #include <linux/stacktrace.h>
31 #include <linux/stackdepot.h>
32 #include <linux/string.h>
33 #include <linux/types.h>
34 #include <linux/memblock.h>
35 
36 #define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)
37 
38 #define STACK_ALLOC_NULL_PROTECTION_BITS 1
39 #define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */
40 #define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER))
41 #define STACK_ALLOC_ALIGN 4
42 #define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \
43 					STACK_ALLOC_ALIGN)
44 #define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \
45 		STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS)
46 #define STACK_ALLOC_SLABS_CAP 8192
47 #define STACK_ALLOC_MAX_SLABS \
48 	(((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \
49 	 (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP)
50 
51 /* The compact structure to store the reference to stacks. */
52 union handle_parts {
53 	depot_stack_handle_t handle;
54 	struct {
55 		u32 slabindex : STACK_ALLOC_INDEX_BITS;
56 		u32 offset : STACK_ALLOC_OFFSET_BITS;
57 		u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS;
58 	};
59 };
60 
61 struct stack_record {
62 	struct stack_record *next;	/* Link in the hashtable */
63 	u32 hash;			/* Hash in the hastable */
64 	u32 size;			/* Number of frames in the stack */
65 	union handle_parts handle;
66 	unsigned long entries[];	/* Variable-sized array of entries. */
67 };
68 
69 static bool __stack_depot_want_early_init __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
70 static bool __stack_depot_early_init_passed __initdata;
71 
72 static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
73 
74 static int depot_index;
75 static int next_slab_inited;
76 static size_t depot_offset;
77 static DEFINE_RAW_SPINLOCK(depot_lock);
78 
init_stack_slab(void ** prealloc)79 static bool init_stack_slab(void **prealloc)
80 {
81 	if (!*prealloc)
82 		return false;
83 	/*
84 	 * This smp_load_acquire() pairs with smp_store_release() to
85 	 * |next_slab_inited| below and in depot_alloc_stack().
86 	 */
87 	if (smp_load_acquire(&next_slab_inited))
88 		return true;
89 	if (stack_slabs[depot_index] == NULL) {
90 		stack_slabs[depot_index] = *prealloc;
91 		*prealloc = NULL;
92 	} else {
93 		/* If this is the last depot slab, do not touch the next one. */
94 		if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) {
95 			stack_slabs[depot_index + 1] = *prealloc;
96 			*prealloc = NULL;
97 		}
98 		/*
99 		 * This smp_store_release pairs with smp_load_acquire() from
100 		 * |next_slab_inited| above and in stack_depot_save().
101 		 */
102 		smp_store_release(&next_slab_inited, 1);
103 	}
104 	return true;
105 }
106 
107 /* Allocation of a new stack in raw storage */
108 static struct stack_record *
depot_alloc_stack(unsigned long * entries,int size,u32 hash,void ** prealloc)109 depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
110 {
111 	struct stack_record *stack;
112 	size_t required_size = struct_size(stack, entries, size);
113 
114 	required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN);
115 
116 	if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) {
117 		if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) {
118 			WARN_ONCE(1, "Stack depot reached limit capacity");
119 			return NULL;
120 		}
121 		depot_index++;
122 		depot_offset = 0;
123 		/*
124 		 * smp_store_release() here pairs with smp_load_acquire() from
125 		 * |next_slab_inited| in stack_depot_save() and
126 		 * init_stack_slab().
127 		 */
128 		if (depot_index + 1 < STACK_ALLOC_MAX_SLABS)
129 			smp_store_release(&next_slab_inited, 0);
130 	}
131 	init_stack_slab(prealloc);
132 	if (stack_slabs[depot_index] == NULL)
133 		return NULL;
134 
135 	stack = stack_slabs[depot_index] + depot_offset;
136 
137 	stack->hash = hash;
138 	stack->size = size;
139 	stack->handle.slabindex = depot_index;
140 	stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
141 	stack->handle.valid = 1;
142 	memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
143 	depot_offset += required_size;
144 
145 	return stack;
146 }
147 
148 #define STACK_HASH_SIZE (1L << CONFIG_STACK_HASH_ORDER)
149 #define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
150 #define STACK_HASH_SEED 0x9747b28c
151 
152 static bool stack_depot_disable;
153 static struct stack_record **stack_table;
154 
is_stack_depot_disabled(char * str)155 static int __init is_stack_depot_disabled(char *str)
156 {
157 	int ret;
158 
159 	ret = kstrtobool(str, &stack_depot_disable);
160 	if (!ret && stack_depot_disable) {
161 		pr_info("Stack Depot is disabled\n");
162 		stack_table = NULL;
163 	}
164 	return 0;
165 }
166 early_param("stack_depot_disable", is_stack_depot_disabled);
167 
stack_depot_want_early_init(void)168 void __init stack_depot_want_early_init(void)
169 {
170 	/* Too late to request early init now */
171 	WARN_ON(__stack_depot_early_init_passed);
172 
173 	__stack_depot_want_early_init = true;
174 }
175 
stack_depot_early_init(void)176 int __init stack_depot_early_init(void)
177 {
178 	size_t size;
179 
180 	/* This is supposed to be called only once, from mm_init() */
181 	if (WARN_ON(__stack_depot_early_init_passed))
182 		return 0;
183 
184 	__stack_depot_early_init_passed = true;
185 
186 	if (!__stack_depot_want_early_init || stack_depot_disable)
187 		return 0;
188 
189 	size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
190 	pr_info("Stack Depot early init allocating hash table with memblock_alloc, %zu bytes\n",
191 		size);
192 	stack_table = memblock_alloc(size, SMP_CACHE_BYTES);
193 
194 	if (!stack_table) {
195 		pr_err("Stack Depot hash table allocation failed, disabling\n");
196 		stack_depot_disable = true;
197 		return -ENOMEM;
198 	}
199 
200 	return 0;
201 }
202 
stack_depot_init(void)203 int stack_depot_init(void)
204 {
205 	static DEFINE_MUTEX(stack_depot_init_mutex);
206 	int ret = 0;
207 
208 	mutex_lock(&stack_depot_init_mutex);
209 	if (!stack_depot_disable && !stack_table) {
210 		pr_info("Stack Depot allocating hash table with kvcalloc\n");
211 		stack_table = kvcalloc(STACK_HASH_SIZE, sizeof(struct stack_record *), GFP_KERNEL);
212 		if (!stack_table) {
213 			pr_err("Stack Depot hash table allocation failed, disabling\n");
214 			stack_depot_disable = true;
215 			ret = -ENOMEM;
216 		}
217 	}
218 	mutex_unlock(&stack_depot_init_mutex);
219 	return ret;
220 }
221 EXPORT_SYMBOL_GPL(stack_depot_init);
222 
223 /* Calculate hash for a stack */
hash_stack(unsigned long * entries,unsigned int size)224 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
225 {
226 	return jhash2((u32 *)entries,
227 		      array_size(size,  sizeof(*entries)) / sizeof(u32),
228 		      STACK_HASH_SEED);
229 }
230 
231 /* Use our own, non-instrumented version of memcmp().
232  *
233  * We actually don't care about the order, just the equality.
234  */
235 static inline
stackdepot_memcmp(const unsigned long * u1,const unsigned long * u2,unsigned int n)236 int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
237 			unsigned int n)
238 {
239 	for ( ; n-- ; u1++, u2++) {
240 		if (*u1 != *u2)
241 			return 1;
242 	}
243 	return 0;
244 }
245 
246 /* Find a stack that is equal to the one stored in entries in the hash */
find_stack(struct stack_record * bucket,unsigned long * entries,int size,u32 hash)247 static inline struct stack_record *find_stack(struct stack_record *bucket,
248 					     unsigned long *entries, int size,
249 					     u32 hash)
250 {
251 	struct stack_record *found;
252 
253 	for (found = bucket; found; found = found->next) {
254 		if (found->hash == hash &&
255 		    found->size == size &&
256 		    !stackdepot_memcmp(entries, found->entries, size))
257 			return found;
258 	}
259 	return NULL;
260 }
261 
262 /**
263  * stack_depot_snprint - print stack entries from a depot into a buffer
264  *
265  * @handle:	Stack depot handle which was returned from
266  *		stack_depot_save().
267  * @buf:	Pointer to the print buffer
268  *
269  * @size:	Size of the print buffer
270  *
271  * @spaces:	Number of leading spaces to print
272  *
273  * Return:	Number of bytes printed.
274  */
stack_depot_snprint(depot_stack_handle_t handle,char * buf,size_t size,int spaces)275 int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
276 		       int spaces)
277 {
278 	unsigned long *entries;
279 	unsigned int nr_entries;
280 
281 	nr_entries = stack_depot_fetch(handle, &entries);
282 	return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
283 						spaces) : 0;
284 }
285 EXPORT_SYMBOL_GPL(stack_depot_snprint);
286 
287 /**
288  * stack_depot_print - print stack entries from a depot
289  *
290  * @stack:		Stack depot handle which was returned from
291  *			stack_depot_save().
292  *
293  */
stack_depot_print(depot_stack_handle_t stack)294 void stack_depot_print(depot_stack_handle_t stack)
295 {
296 	unsigned long *entries;
297 	unsigned int nr_entries;
298 
299 	nr_entries = stack_depot_fetch(stack, &entries);
300 	if (nr_entries > 0)
301 		stack_trace_print(entries, nr_entries, 0);
302 }
303 EXPORT_SYMBOL_GPL(stack_depot_print);
304 
305 /**
306  * stack_depot_fetch - Fetch stack entries from a depot
307  *
308  * @handle:		Stack depot handle which was returned from
309  *			stack_depot_save().
310  * @entries:		Pointer to store the entries address
311  *
312  * Return: The number of trace entries for this depot.
313  */
stack_depot_fetch(depot_stack_handle_t handle,unsigned long ** entries)314 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
315 			       unsigned long **entries)
316 {
317 	union handle_parts parts = { .handle = handle };
318 	void *slab;
319 	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
320 	struct stack_record *stack;
321 
322 	*entries = NULL;
323 	if (!handle)
324 		return 0;
325 
326 	if (parts.slabindex > depot_index) {
327 		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
328 			parts.slabindex, depot_index, handle);
329 		return 0;
330 	}
331 	slab = stack_slabs[parts.slabindex];
332 	if (!slab)
333 		return 0;
334 	stack = slab + offset;
335 
336 	*entries = stack->entries;
337 	return stack->size;
338 }
339 EXPORT_SYMBOL_GPL(stack_depot_fetch);
340 
341 /**
342  * __stack_depot_save - Save a stack trace from an array
343  *
344  * @entries:		Pointer to storage array
345  * @nr_entries:		Size of the storage array
346  * @alloc_flags:	Allocation gfp flags
347  * @can_alloc:		Allocate stack slabs (increased chance of failure if false)
348  *
349  * Saves a stack trace from @entries array of size @nr_entries. If @can_alloc is
350  * %true, is allowed to replenish the stack slab pool in case no space is left
351  * (allocates using GFP flags of @alloc_flags). If @can_alloc is %false, avoids
352  * any allocations and will fail if no space is left to store the stack trace.
353  *
354  * If the stack trace in @entries is from an interrupt, only the portion up to
355  * interrupt entry is saved.
356  *
357  * Context: Any context, but setting @can_alloc to %false is required if
358  *          alloc_pages() cannot be used from the current context. Currently
359  *          this is the case from contexts where neither %GFP_ATOMIC nor
360  *          %GFP_NOWAIT can be used (NMI, raw_spin_lock).
361  *
362  * Return: The handle of the stack struct stored in depot, 0 on failure.
363  */
__stack_depot_save(unsigned long * entries,unsigned int nr_entries,gfp_t alloc_flags,bool can_alloc)364 depot_stack_handle_t __stack_depot_save(unsigned long *entries,
365 					unsigned int nr_entries,
366 					gfp_t alloc_flags, bool can_alloc)
367 {
368 	struct stack_record *found = NULL, **bucket;
369 	depot_stack_handle_t retval = 0;
370 	struct page *page = NULL;
371 	void *prealloc = NULL;
372 	unsigned long flags;
373 	u32 hash;
374 
375 	/*
376 	 * If this stack trace is from an interrupt, including anything before
377 	 * interrupt entry usually leads to unbounded stackdepot growth.
378 	 *
379 	 * Because use of filter_irq_stacks() is a requirement to ensure
380 	 * stackdepot can efficiently deduplicate interrupt stacks, always
381 	 * filter_irq_stacks() to simplify all callers' use of stackdepot.
382 	 */
383 	nr_entries = filter_irq_stacks(entries, nr_entries);
384 
385 	if (unlikely(nr_entries == 0) || stack_depot_disable)
386 		goto fast_exit;
387 
388 	hash = hash_stack(entries, nr_entries);
389 	bucket = &stack_table[hash & STACK_HASH_MASK];
390 
391 	/*
392 	 * Fast path: look the stack trace up without locking.
393 	 * The smp_load_acquire() here pairs with smp_store_release() to
394 	 * |bucket| below.
395 	 */
396 	found = find_stack(smp_load_acquire(bucket), entries,
397 			   nr_entries, hash);
398 	if (found)
399 		goto exit;
400 
401 	/*
402 	 * Check if the current or the next stack slab need to be initialized.
403 	 * If so, allocate the memory - we won't be able to do that under the
404 	 * lock.
405 	 *
406 	 * The smp_load_acquire() here pairs with smp_store_release() to
407 	 * |next_slab_inited| in depot_alloc_stack() and init_stack_slab().
408 	 */
409 	if (unlikely(can_alloc && !smp_load_acquire(&next_slab_inited))) {
410 		/*
411 		 * Zero out zone modifiers, as we don't have specific zone
412 		 * requirements. Keep the flags related to allocation in atomic
413 		 * contexts and I/O.
414 		 */
415 		alloc_flags &= ~GFP_ZONEMASK;
416 		alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
417 		alloc_flags |= __GFP_NOWARN;
418 		page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
419 		if (page)
420 			prealloc = page_address(page);
421 	}
422 
423 	raw_spin_lock_irqsave(&depot_lock, flags);
424 
425 	found = find_stack(*bucket, entries, nr_entries, hash);
426 	if (!found) {
427 		struct stack_record *new = depot_alloc_stack(entries, nr_entries, hash, &prealloc);
428 
429 		if (new) {
430 			new->next = *bucket;
431 			/*
432 			 * This smp_store_release() pairs with
433 			 * smp_load_acquire() from |bucket| above.
434 			 */
435 			smp_store_release(bucket, new);
436 			found = new;
437 		}
438 	} else if (prealloc) {
439 		/*
440 		 * We didn't need to store this stack trace, but let's keep
441 		 * the preallocated memory for the future.
442 		 */
443 		WARN_ON(!init_stack_slab(&prealloc));
444 	}
445 
446 	raw_spin_unlock_irqrestore(&depot_lock, flags);
447 exit:
448 	if (prealloc) {
449 		/* Nobody used this memory, ok to free it. */
450 		free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
451 	}
452 	if (found)
453 		retval = found->handle.handle;
454 fast_exit:
455 	return retval;
456 }
457 EXPORT_SYMBOL_GPL(__stack_depot_save);
458 
459 /**
460  * stack_depot_save - Save a stack trace from an array
461  *
462  * @entries:		Pointer to storage array
463  * @nr_entries:		Size of the storage array
464  * @alloc_flags:	Allocation gfp flags
465  *
466  * Context: Contexts where allocations via alloc_pages() are allowed.
467  *          See __stack_depot_save() for more details.
468  *
469  * Return: The handle of the stack struct stored in depot, 0 on failure.
470  */
stack_depot_save(unsigned long * entries,unsigned int nr_entries,gfp_t alloc_flags)471 depot_stack_handle_t stack_depot_save(unsigned long *entries,
472 				      unsigned int nr_entries,
473 				      gfp_t alloc_flags)
474 {
475 	return __stack_depot_save(entries, nr_entries, alloc_flags, true);
476 }
477 EXPORT_SYMBOL_GPL(stack_depot_save);
478