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. */
51 union 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
60 struct 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
68 static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
69
70 static int depot_index;
71 static int next_slab_inited;
72 static size_t depot_offset;
73 static DEFINE_SPINLOCK(depot_lock);
74
init_stack_slab(void ** prealloc)75 static 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 */
depot_alloc_stack(unsigned long * entries,int size,u32 hash,void ** prealloc,gfp_t alloc_flags)104 static 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
150 static struct stack_record *stack_table[STACK_HASH_SIZE] = {
151 [0 ... STACK_HASH_SIZE - 1] = NULL
152 };
153
154 /* Calculate hash for a stack */
hash_stack(unsigned long * entries,unsigned int size)155 static 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 */
166 static inline
stackdepot_memcmp(const unsigned long * u1,const unsigned long * u2,unsigned int n)167 int 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 */
find_stack(struct stack_record * bucket,unsigned long * entries,int size,u32 hash)178 static 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 */
stack_depot_fetch(depot_stack_handle_t handle,unsigned long ** entries)202 unsigned 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 }
224 EXPORT_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 */
stack_depot_save(unsigned long * entries,unsigned int nr_entries,gfp_t alloc_flags)235 depot_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);
309 exit:
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;
316 fast_exit:
317 return retval;
318 }
319 EXPORT_SYMBOL_GPL(stack_depot_save);
320
in_irqentry_text(unsigned long ptr)321 static 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
filter_irq_stacks(unsigned long * entries,unsigned int nr_entries)329 unsigned 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 }
342 EXPORT_SYMBOL_GPL(filter_irq_stacks);
343
