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/interrupt.h>
 24#include <linux/jhash.h>
 25#include <linux/kernel.h>
 26#include <linux/mm.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. */
 52union 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
 61struct 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
 69static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
 70
 71static int depot_index;
 72static int next_slab_inited;
 73static size_t depot_offset;
 74static DEFINE_RAW_SPINLOCK(depot_lock);
 75
 76static bool init_stack_slab(void **prealloc)
 77{
 78	if (!*prealloc)
 79		return false;
 80	/*
 81	 * This smp_load_acquire() pairs with smp_store_release() to
 82	 * |next_slab_inited| below and in depot_alloc_stack().
 83	 */
 84	if (smp_load_acquire(&next_slab_inited))
 85		return true;
 86	if (stack_slabs[depot_index] == NULL) {
 87		stack_slabs[depot_index] = *prealloc;
 88		*prealloc = NULL;
 89	} else {
 90		/* If this is the last depot slab, do not touch the next one. */
 91		if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) {
 92			stack_slabs[depot_index + 1] = *prealloc;
 93			*prealloc = NULL;
 94		}
 95		/*
 96		 * This smp_store_release pairs with smp_load_acquire() from
 97		 * |next_slab_inited| above and in stack_depot_save().
 98		 */
 99		smp_store_release(&next_slab_inited, 1);
100	}
101	return true;
102}
103
104/* Allocation of a new stack in raw storage */
105static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
106		u32 hash, void **prealloc, gfp_t alloc_flags)
107{
108	struct stack_record *stack;
109	size_t required_size = struct_size(stack, entries, size);
110
111	required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN);
112
113	if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) {
114		if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) {
115			WARN_ONCE(1, "Stack depot reached limit capacity");
116			return NULL;
117		}
118		depot_index++;
119		depot_offset = 0;
120		/*
121		 * smp_store_release() here pairs with smp_load_acquire() from
122		 * |next_slab_inited| in stack_depot_save() and
123		 * init_stack_slab().
124		 */
125		if (depot_index + 1 < STACK_ALLOC_MAX_SLABS)
126			smp_store_release(&next_slab_inited, 0);
127	}
128	init_stack_slab(prealloc);
129	if (stack_slabs[depot_index] == NULL)
130		return NULL;
131
132	stack = stack_slabs[depot_index] + depot_offset;
133
134	stack->hash = hash;
135	stack->size = size;
136	stack->handle.slabindex = depot_index;
137	stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
138	stack->handle.valid = 1;
139	memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
140	depot_offset += required_size;
141
142	return stack;
143}
144
145#define STACK_HASH_SIZE (1L << CONFIG_STACK_HASH_ORDER)
146#define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
147#define STACK_HASH_SEED 0x9747b28c
148
149static bool stack_depot_disable;
150static struct stack_record **stack_table;
151
152static int __init is_stack_depot_disabled(char *str)
153{
154	int ret;
155
156	ret = kstrtobool(str, &stack_depot_disable);
157	if (!ret && stack_depot_disable) {
158		pr_info("Stack Depot is disabled\n");
159		stack_table = NULL;
160	}
161	return 0;
162}
163early_param("stack_depot_disable", is_stack_depot_disabled);
164
165int __init stack_depot_init(void)
166{
167	if (!stack_depot_disable) {
168		size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
169		int i;
170
171		stack_table = memblock_alloc(size, size);
172		for (i = 0; i < STACK_HASH_SIZE;  i++)
173			stack_table[i] = NULL;
174	}
175	return 0;
176}
177
178/* Calculate hash for a stack */
179static inline u32 hash_stack(unsigned long *entries, unsigned int size)
180{
181	return jhash2((u32 *)entries,
182		      array_size(size,  sizeof(*entries)) / sizeof(u32),
183		      STACK_HASH_SEED);
184}
185
186/* Use our own, non-instrumented version of memcmp().
187 *
188 * We actually don't care about the order, just the equality.
189 */
190static inline
191int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
192			unsigned int n)
193{
194	for ( ; n-- ; u1++, u2++) {
195		if (*u1 != *u2)
196			return 1;
197	}
198	return 0;
199}
200
201/* Find a stack that is equal to the one stored in entries in the hash */
202static inline struct stack_record *find_stack(struct stack_record *bucket,
203					     unsigned long *entries, int size,
204					     u32 hash)
205{
206	struct stack_record *found;
207
208	for (found = bucket; found; found = found->next) {
209		if (found->hash == hash &&
210		    found->size == size &&
211		    !stackdepot_memcmp(entries, found->entries, size))
212			return found;
213	}
214	return NULL;
215}
216
217/**
218 * stack_depot_fetch - Fetch stack entries from a depot
219 *
220 * @handle:		Stack depot handle which was returned from
221 *			stack_depot_save().
222 * @entries:		Pointer to store the entries address
223 *
224 * Return: The number of trace entries for this depot.
225 */
226unsigned int stack_depot_fetch(depot_stack_handle_t handle,
227			       unsigned long **entries)
228{
229	union handle_parts parts = { .handle = handle };
230	void *slab;
231	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
232	struct stack_record *stack;
233
234	*entries = NULL;
235	if (parts.slabindex > depot_index) {
236		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
237			parts.slabindex, depot_index, handle);
238		return 0;
239	}
240	slab = stack_slabs[parts.slabindex];
241	if (!slab)
242		return 0;
243	stack = slab + offset;
244
245	*entries = stack->entries;
246	return stack->size;
247}
248EXPORT_SYMBOL_GPL(stack_depot_fetch);
249
250/**
251 * stack_depot_save - Save a stack trace from an array
252 *
253 * @entries:		Pointer to storage array
254 * @nr_entries:		Size of the storage array
255 * @alloc_flags:	Allocation gfp flags
256 *
257 * Return: The handle of the stack struct stored in depot
258 */
259depot_stack_handle_t stack_depot_save(unsigned long *entries,
260				      unsigned int nr_entries,
261				      gfp_t alloc_flags)
262{
263	struct stack_record *found = NULL, **bucket;
264	depot_stack_handle_t retval = 0;
265	struct page *page = NULL;
266	void *prealloc = NULL;
267	unsigned long flags;
268	u32 hash;
269
270	if (unlikely(nr_entries == 0) || stack_depot_disable)
271		goto fast_exit;
272
273	hash = hash_stack(entries, nr_entries);
274	bucket = &stack_table[hash & STACK_HASH_MASK];
275
276	/*
277	 * Fast path: look the stack trace up without locking.
278	 * The smp_load_acquire() here pairs with smp_store_release() to
279	 * |bucket| below.
280	 */
281	found = find_stack(smp_load_acquire(bucket), entries,
282			   nr_entries, hash);
283	if (found)
284		goto exit;
285
286	/*
287	 * Check if the current or the next stack slab need to be initialized.
288	 * If so, allocate the memory - we won't be able to do that under the
289	 * lock.
290	 *
291	 * The smp_load_acquire() here pairs with smp_store_release() to
292	 * |next_slab_inited| in depot_alloc_stack() and init_stack_slab().
293	 */
294	if (unlikely(!smp_load_acquire(&next_slab_inited))) {
295		/*
296		 * Zero out zone modifiers, as we don't have specific zone
297		 * requirements. Keep the flags related to allocation in atomic
298		 * contexts and I/O.
299		 */
300		alloc_flags &= ~GFP_ZONEMASK;
301		alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
302		alloc_flags |= __GFP_NOWARN;
303		page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
304		if (page)
305			prealloc = page_address(page);
306	}
307
308	raw_spin_lock_irqsave(&depot_lock, flags);
309
310	found = find_stack(*bucket, entries, nr_entries, hash);
311	if (!found) {
312		struct stack_record *new =
313			depot_alloc_stack(entries, nr_entries,
314					  hash, &prealloc, alloc_flags);
315		if (new) {
316			new->next = *bucket;
317			/*
318			 * This smp_store_release() pairs with
319			 * smp_load_acquire() from |bucket| above.
320			 */
321			smp_store_release(bucket, new);
322			found = new;
323		}
324	} else if (prealloc) {
325		/*
326		 * We didn't need to store this stack trace, but let's keep
327		 * the preallocated memory for the future.
328		 */
329		WARN_ON(!init_stack_slab(&prealloc));
330	}
331
332	raw_spin_unlock_irqrestore(&depot_lock, flags);
333exit:
334	if (prealloc) {
335		/* Nobody used this memory, ok to free it. */
336		free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
337	}
338	if (found)
339		retval = found->handle.handle;
340fast_exit:
341	return retval;
342}
343EXPORT_SYMBOL_GPL(stack_depot_save);
344
345static inline int in_irqentry_text(unsigned long ptr)
346{
347	return (ptr >= (unsigned long)&__irqentry_text_start &&
348		ptr < (unsigned long)&__irqentry_text_end) ||
349		(ptr >= (unsigned long)&__softirqentry_text_start &&
350		 ptr < (unsigned long)&__softirqentry_text_end);
351}
352
353unsigned int filter_irq_stacks(unsigned long *entries,
354					     unsigned int nr_entries)
355{
356	unsigned int i;
357
358	for (i = 0; i < nr_entries; i++) {
359		if (in_irqentry_text(entries[i])) {
360			/* Include the irqentry function into the stack. */
361			return i + 1;
362		}
363	}
364	return nr_entries;
365}
366EXPORT_SYMBOL_GPL(filter_irq_stacks);