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 contiguos 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
 35#define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)
 36
 37#define STACK_ALLOC_NULL_PROTECTION_BITS 1
 38#define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */
 39#define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER))
 40#define STACK_ALLOC_ALIGN 4
 41#define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \
 42					STACK_ALLOC_ALIGN)
 43#define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \
 44		STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS)
 45#define STACK_ALLOC_SLABS_CAP 8192
 46#define STACK_ALLOC_MAX_SLABS \
 47	(((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \
 48	 (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP)
 49
 50/* The compact structure to store the reference to stacks. */
 51union handle_parts {
 52	depot_stack_handle_t handle;
 53	struct {
 54		u32 slabindex : STACK_ALLOC_INDEX_BITS;
 55		u32 offset : STACK_ALLOC_OFFSET_BITS;
 56		u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS;
 57	};
 58};
 59
 60struct stack_record {
 61	struct stack_record *next;	/* Link in the hashtable */
 62	u32 hash;			/* Hash in the hastable */
 63	u32 size;			/* Number of frames in the stack */
 64	union handle_parts handle;
 65	unsigned long entries[1];	/* Variable-sized array of entries. */
 66};
 67
 68static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
 69
 70static int depot_index;
 71static int next_slab_inited;
 72static size_t depot_offset;
 73static DEFINE_SPINLOCK(depot_lock);
 74
 75static bool init_stack_slab(void **prealloc)
 76{
 77	if (!*prealloc)
 78		return false;
 79	/*
 80	 * This smp_load_acquire() pairs with smp_store_release() to
 81	 * |next_slab_inited| below and in depot_alloc_stack().
 82	 */
 83	if (smp_load_acquire(&next_slab_inited))
 84		return true;
 85	if (stack_slabs[depot_index] == NULL) {
 86		stack_slabs[depot_index] = *prealloc;
 87		*prealloc = NULL;
 88	} else {
 89		/* If this is the last depot slab, do not touch the next one. */
 90		if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) {
 91			stack_slabs[depot_index + 1] = *prealloc;
 92			*prealloc = NULL;
 93		}
 94		/*
 95		 * This smp_store_release pairs with smp_load_acquire() from
 96		 * |next_slab_inited| above and in stack_depot_save().
 97		 */
 98		smp_store_release(&next_slab_inited, 1);
 99	}
100	return true;
101}
102
103/* Allocation of a new stack in raw storage */
104static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
105		u32 hash, void **prealloc, gfp_t alloc_flags)
106{
107	int required_size = offsetof(struct stack_record, entries) +
108		sizeof(unsigned long) * size;
109	struct stack_record *stack;
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, size * sizeof(unsigned long));
140	depot_offset += required_size;
141
142	return stack;
143}
144
145#define STACK_HASH_ORDER 20
146#define STACK_HASH_SIZE (1L << STACK_HASH_ORDER)
147#define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
148#define STACK_HASH_SEED 0x9747b28c
149
150static struct stack_record *stack_table[STACK_HASH_SIZE] = {
151	[0 ...	STACK_HASH_SIZE - 1] = NULL
152};
153
154/* Calculate hash for a stack */
155static inline u32 hash_stack(unsigned long *entries, unsigned int size)
156{
157	return jhash2((u32 *)entries,
158			       size * sizeof(unsigned long) / sizeof(u32),
159			       STACK_HASH_SEED);
160}
161
162/* Use our own, non-instrumented version of memcmp().
163 *
164 * We actually don't care about the order, just the equality.
165 */
166static inline
167int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
168			unsigned int n)
169{
170	for ( ; n-- ; u1++, u2++) {
171		if (*u1 != *u2)
172			return 1;
173	}
174	return 0;
175}
176
177/* Find a stack that is equal to the one stored in entries in the hash */
178static inline struct stack_record *find_stack(struct stack_record *bucket,
179					     unsigned long *entries, int size,
180					     u32 hash)
181{
182	struct stack_record *found;
183
184	for (found = bucket; found; found = found->next) {
185		if (found->hash == hash &&
186		    found->size == size &&
187		    !stackdepot_memcmp(entries, found->entries, size))
188			return found;
189	}
190	return NULL;
191}
192
193/**
194 * stack_depot_fetch - Fetch stack entries from a depot
195 *
196 * @handle:		Stack depot handle which was returned from
197 *			stack_depot_save().
198 * @entries:		Pointer to store the entries address
199 *
200 * Return: The number of trace entries for this depot.
201 */
202unsigned int stack_depot_fetch(depot_stack_handle_t handle,
203			       unsigned long **entries)
204{
205	union handle_parts parts = { .handle = handle };
206	void *slab;
207	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
208	struct stack_record *stack;
209
210	*entries = NULL;
211	if (parts.slabindex > depot_index) {
212		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
213			parts.slabindex, depot_index, handle);
214		return 0;
215	}
216	slab = stack_slabs[parts.slabindex];
217	if (!slab)
218		return 0;
219	stack = slab + offset;
220
221	*entries = stack->entries;
222	return stack->size;
223}
224EXPORT_SYMBOL_GPL(stack_depot_fetch);
225
226/**
227 * stack_depot_save - Save a stack trace from an array
228 *
229 * @entries:		Pointer to storage array
230 * @nr_entries:		Size of the storage array
231 * @alloc_flags:	Allocation gfp flags
232 *
233 * Return: The handle of the stack struct stored in depot
234 */
235depot_stack_handle_t stack_depot_save(unsigned long *entries,
236				      unsigned int nr_entries,
237				      gfp_t alloc_flags)
238{
239	struct stack_record *found = NULL, **bucket;
240	depot_stack_handle_t retval = 0;
241	struct page *page = NULL;
242	void *prealloc = NULL;
243	unsigned long flags;
244	u32 hash;
245
246	if (unlikely(nr_entries == 0))
247		goto fast_exit;
248
249	hash = hash_stack(entries, nr_entries);
250	bucket = &stack_table[hash & STACK_HASH_MASK];
251
252	/*
253	 * Fast path: look the stack trace up without locking.
254	 * The smp_load_acquire() here pairs with smp_store_release() to
255	 * |bucket| below.
256	 */
257	found = find_stack(smp_load_acquire(bucket), entries,
258			   nr_entries, hash);
259	if (found)
260		goto exit;
261
262	/*
263	 * Check if the current or the next stack slab need to be initialized.
264	 * If so, allocate the memory - we won't be able to do that under the
265	 * lock.
266	 *
267	 * The smp_load_acquire() here pairs with smp_store_release() to
268	 * |next_slab_inited| in depot_alloc_stack() and init_stack_slab().
269	 */
270	if (unlikely(!smp_load_acquire(&next_slab_inited))) {
271		/*
272		 * Zero out zone modifiers, as we don't have specific zone
273		 * requirements. Keep the flags related to allocation in atomic
274		 * contexts and I/O.
275		 */
276		alloc_flags &= ~GFP_ZONEMASK;
277		alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
278		alloc_flags |= __GFP_NOWARN;
279		page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
280		if (page)
281			prealloc = page_address(page);
282	}
283
284	spin_lock_irqsave(&depot_lock, flags);
285
286	found = find_stack(*bucket, entries, nr_entries, hash);
287	if (!found) {
288		struct stack_record *new =
289			depot_alloc_stack(entries, nr_entries,
290					  hash, &prealloc, alloc_flags);
291		if (new) {
292			new->next = *bucket;
293			/*
294			 * This smp_store_release() pairs with
295			 * smp_load_acquire() from |bucket| above.
296			 */
297			smp_store_release(bucket, new);
298			found = new;
299		}
300	} else if (prealloc) {
301		/*
302		 * We didn't need to store this stack trace, but let's keep
303		 * the preallocated memory for the future.
304		 */
305		WARN_ON(!init_stack_slab(&prealloc));
306	}
307
308	spin_unlock_irqrestore(&depot_lock, flags);
309exit:
310	if (prealloc) {
311		/* Nobody used this memory, ok to free it. */
312		free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
313	}
314	if (found)
315		retval = found->handle.handle;
316fast_exit:
317	return retval;
318}
319EXPORT_SYMBOL_GPL(stack_depot_save);
320
321static inline int in_irqentry_text(unsigned long ptr)
322{
323	return (ptr >= (unsigned long)&__irqentry_text_start &&
324		ptr < (unsigned long)&__irqentry_text_end) ||
325		(ptr >= (unsigned long)&__softirqentry_text_start &&
326		 ptr < (unsigned long)&__softirqentry_text_end);
327}
328
329unsigned int filter_irq_stacks(unsigned long *entries,
330					     unsigned int nr_entries)
331{
332	unsigned int i;
333
334	for (i = 0; i < nr_entries; i++) {
335		if (in_irqentry_text(entries[i])) {
336			/* Include the irqentry function into the stack. */
337			return i + 1;
338		}
339	}
340	return nr_entries;
341}
342EXPORT_SYMBOL_GPL(filter_irq_stacks);