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1802d0be | 1 | // SPDX-License-Identifier: GPL-2.0-only |
cd11016e AP |
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. | |
cd11016e AP |
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/percpu.h> | |
27 | #include <linux/printk.h> | |
28 | #include <linux/slab.h> | |
29 | #include <linux/stacktrace.h> | |
30 | #include <linux/stackdepot.h> | |
31 | #include <linux/string.h> | |
32 | #include <linux/types.h> | |
33 | ||
34 | #define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8) | |
35 | ||
7c31190b | 36 | #define STACK_ALLOC_NULL_PROTECTION_BITS 1 |
cd11016e AP |
37 | #define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */ |
38 | #define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER)) | |
39 | #define STACK_ALLOC_ALIGN 4 | |
40 | #define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \ | |
41 | STACK_ALLOC_ALIGN) | |
7c31190b JK |
42 | #define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \ |
43 | STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS) | |
02754e0a | 44 | #define STACK_ALLOC_SLABS_CAP 8192 |
cd11016e AP |
45 | #define STACK_ALLOC_MAX_SLABS \ |
46 | (((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \ | |
47 | (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP) | |
48 | ||
49 | /* The compact structure to store the reference to stacks. */ | |
50 | union handle_parts { | |
51 | depot_stack_handle_t handle; | |
52 | struct { | |
53 | u32 slabindex : STACK_ALLOC_INDEX_BITS; | |
54 | u32 offset : STACK_ALLOC_OFFSET_BITS; | |
7c31190b | 55 | u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS; |
cd11016e AP |
56 | }; |
57 | }; | |
58 | ||
59 | struct stack_record { | |
60 | struct stack_record *next; /* Link in the hashtable */ | |
61 | u32 hash; /* Hash in the hastable */ | |
62 | u32 size; /* Number of frames in the stack */ | |
63 | union handle_parts handle; | |
64 | unsigned long entries[1]; /* Variable-sized array of entries. */ | |
65 | }; | |
66 | ||
67 | static void *stack_slabs[STACK_ALLOC_MAX_SLABS]; | |
68 | ||
69 | static int depot_index; | |
70 | static int next_slab_inited; | |
71 | static size_t depot_offset; | |
72 | static DEFINE_SPINLOCK(depot_lock); | |
73 | ||
74 | static bool init_stack_slab(void **prealloc) | |
75 | { | |
76 | if (!*prealloc) | |
77 | return false; | |
78 | /* | |
79 | * This smp_load_acquire() pairs with smp_store_release() to | |
80 | * |next_slab_inited| below and in depot_alloc_stack(). | |
81 | */ | |
82 | if (smp_load_acquire(&next_slab_inited)) | |
83 | return true; | |
84 | if (stack_slabs[depot_index] == NULL) { | |
85 | stack_slabs[depot_index] = *prealloc; | |
86 | } else { | |
87 | stack_slabs[depot_index + 1] = *prealloc; | |
88 | /* | |
89 | * This smp_store_release pairs with smp_load_acquire() from | |
ee050dc8 | 90 | * |next_slab_inited| above and in stack_depot_save(). |
cd11016e AP |
91 | */ |
92 | smp_store_release(&next_slab_inited, 1); | |
93 | } | |
94 | *prealloc = NULL; | |
95 | return true; | |
96 | } | |
97 | ||
98 | /* Allocation of a new stack in raw storage */ | |
99 | static struct stack_record *depot_alloc_stack(unsigned long *entries, int size, | |
100 | u32 hash, void **prealloc, gfp_t alloc_flags) | |
101 | { | |
102 | int required_size = offsetof(struct stack_record, entries) + | |
103 | sizeof(unsigned long) * size; | |
104 | struct stack_record *stack; | |
105 | ||
106 | required_size = ALIGN(required_size, 1 << STACK_ALLOC_ALIGN); | |
107 | ||
108 | if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) { | |
109 | if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) { | |
110 | WARN_ONCE(1, "Stack depot reached limit capacity"); | |
111 | return NULL; | |
112 | } | |
113 | depot_index++; | |
114 | depot_offset = 0; | |
115 | /* | |
116 | * smp_store_release() here pairs with smp_load_acquire() from | |
ee050dc8 | 117 | * |next_slab_inited| in stack_depot_save() and |
cd11016e AP |
118 | * init_stack_slab(). |
119 | */ | |
120 | if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) | |
121 | smp_store_release(&next_slab_inited, 0); | |
122 | } | |
123 | init_stack_slab(prealloc); | |
124 | if (stack_slabs[depot_index] == NULL) | |
125 | return NULL; | |
126 | ||
127 | stack = stack_slabs[depot_index] + depot_offset; | |
128 | ||
129 | stack->hash = hash; | |
130 | stack->size = size; | |
131 | stack->handle.slabindex = depot_index; | |
132 | stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN; | |
7c31190b | 133 | stack->handle.valid = 1; |
cd11016e AP |
134 | memcpy(stack->entries, entries, size * sizeof(unsigned long)); |
135 | depot_offset += required_size; | |
136 | ||
137 | return stack; | |
138 | } | |
139 | ||
140 | #define STACK_HASH_ORDER 20 | |
141 | #define STACK_HASH_SIZE (1L << STACK_HASH_ORDER) | |
142 | #define STACK_HASH_MASK (STACK_HASH_SIZE - 1) | |
143 | #define STACK_HASH_SEED 0x9747b28c | |
144 | ||
145 | static struct stack_record *stack_table[STACK_HASH_SIZE] = { | |
146 | [0 ... STACK_HASH_SIZE - 1] = NULL | |
147 | }; | |
148 | ||
149 | /* Calculate hash for a stack */ | |
150 | static inline u32 hash_stack(unsigned long *entries, unsigned int size) | |
151 | { | |
152 | return jhash2((u32 *)entries, | |
153 | size * sizeof(unsigned long) / sizeof(u32), | |
154 | STACK_HASH_SEED); | |
155 | } | |
156 | ||
a571b272 AP |
157 | /* Use our own, non-instrumented version of memcmp(). |
158 | * | |
159 | * We actually don't care about the order, just the equality. | |
160 | */ | |
161 | static inline | |
162 | int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2, | |
163 | unsigned int n) | |
164 | { | |
165 | for ( ; n-- ; u1++, u2++) { | |
166 | if (*u1 != *u2) | |
167 | return 1; | |
168 | } | |
169 | return 0; | |
170 | } | |
171 | ||
cd11016e AP |
172 | /* Find a stack that is equal to the one stored in entries in the hash */ |
173 | static inline struct stack_record *find_stack(struct stack_record *bucket, | |
174 | unsigned long *entries, int size, | |
175 | u32 hash) | |
176 | { | |
177 | struct stack_record *found; | |
178 | ||
179 | for (found = bucket; found; found = found->next) { | |
180 | if (found->hash == hash && | |
181 | found->size == size && | |
a571b272 | 182 | !stackdepot_memcmp(entries, found->entries, size)) |
cd11016e | 183 | return found; |
cd11016e AP |
184 | } |
185 | return NULL; | |
186 | } | |
187 | ||
c0cfc337 TG |
188 | /** |
189 | * stack_depot_fetch - Fetch stack entries from a depot | |
190 | * | |
191 | * @handle: Stack depot handle which was returned from | |
192 | * stack_depot_save(). | |
193 | * @entries: Pointer to store the entries address | |
194 | * | |
195 | * Return: The number of trace entries for this depot. | |
196 | */ | |
197 | unsigned int stack_depot_fetch(depot_stack_handle_t handle, | |
198 | unsigned long **entries) | |
cd11016e AP |
199 | { |
200 | union handle_parts parts = { .handle = handle }; | |
201 | void *slab = stack_slabs[parts.slabindex]; | |
202 | size_t offset = parts.offset << STACK_ALLOC_ALIGN; | |
203 | struct stack_record *stack = slab + offset; | |
204 | ||
c0cfc337 TG |
205 | *entries = stack->entries; |
206 | return stack->size; | |
207 | } | |
208 | EXPORT_SYMBOL_GPL(stack_depot_fetch); | |
209 | ||
cd11016e | 210 | /** |
c0cfc337 TG |
211 | * stack_depot_save - Save a stack trace from an array |
212 | * | |
213 | * @entries: Pointer to storage array | |
214 | * @nr_entries: Size of the storage array | |
215 | * @alloc_flags: Allocation gfp flags | |
cd11016e | 216 | * |
c0cfc337 | 217 | * Return: The handle of the stack struct stored in depot |
cd11016e | 218 | */ |
c0cfc337 TG |
219 | depot_stack_handle_t stack_depot_save(unsigned long *entries, |
220 | unsigned int nr_entries, | |
221 | gfp_t alloc_flags) | |
cd11016e | 222 | { |
cd11016e | 223 | struct stack_record *found = NULL, **bucket; |
c0cfc337 | 224 | depot_stack_handle_t retval = 0; |
cd11016e AP |
225 | struct page *page = NULL; |
226 | void *prealloc = NULL; | |
c0cfc337 TG |
227 | unsigned long flags; |
228 | u32 hash; | |
cd11016e | 229 | |
c0cfc337 | 230 | if (unlikely(nr_entries == 0)) |
cd11016e AP |
231 | goto fast_exit; |
232 | ||
c0cfc337 | 233 | hash = hash_stack(entries, nr_entries); |
cd11016e AP |
234 | bucket = &stack_table[hash & STACK_HASH_MASK]; |
235 | ||
236 | /* | |
237 | * Fast path: look the stack trace up without locking. | |
238 | * The smp_load_acquire() here pairs with smp_store_release() to | |
239 | * |bucket| below. | |
240 | */ | |
c0cfc337 TG |
241 | found = find_stack(smp_load_acquire(bucket), entries, |
242 | nr_entries, hash); | |
cd11016e AP |
243 | if (found) |
244 | goto exit; | |
245 | ||
246 | /* | |
247 | * Check if the current or the next stack slab need to be initialized. | |
248 | * If so, allocate the memory - we won't be able to do that under the | |
249 | * lock. | |
250 | * | |
251 | * The smp_load_acquire() here pairs with smp_store_release() to | |
252 | * |next_slab_inited| in depot_alloc_stack() and init_stack_slab(). | |
253 | */ | |
254 | if (unlikely(!smp_load_acquire(&next_slab_inited))) { | |
255 | /* | |
256 | * Zero out zone modifiers, as we don't have specific zone | |
257 | * requirements. Keep the flags related to allocation in atomic | |
258 | * contexts and I/O. | |
259 | */ | |
260 | alloc_flags &= ~GFP_ZONEMASK; | |
261 | alloc_flags &= (GFP_ATOMIC | GFP_KERNEL); | |
87cc271d | 262 | alloc_flags |= __GFP_NOWARN; |
cd11016e AP |
263 | page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER); |
264 | if (page) | |
265 | prealloc = page_address(page); | |
266 | } | |
267 | ||
268 | spin_lock_irqsave(&depot_lock, flags); | |
269 | ||
c0cfc337 | 270 | found = find_stack(*bucket, entries, nr_entries, hash); |
cd11016e AP |
271 | if (!found) { |
272 | struct stack_record *new = | |
c0cfc337 | 273 | depot_alloc_stack(entries, nr_entries, |
cd11016e AP |
274 | hash, &prealloc, alloc_flags); |
275 | if (new) { | |
276 | new->next = *bucket; | |
277 | /* | |
278 | * This smp_store_release() pairs with | |
279 | * smp_load_acquire() from |bucket| above. | |
280 | */ | |
281 | smp_store_release(bucket, new); | |
282 | found = new; | |
283 | } | |
284 | } else if (prealloc) { | |
285 | /* | |
286 | * We didn't need to store this stack trace, but let's keep | |
287 | * the preallocated memory for the future. | |
288 | */ | |
289 | WARN_ON(!init_stack_slab(&prealloc)); | |
290 | } | |
291 | ||
292 | spin_unlock_irqrestore(&depot_lock, flags); | |
293 | exit: | |
294 | if (prealloc) { | |
295 | /* Nobody used this memory, ok to free it. */ | |
296 | free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER); | |
297 | } | |
298 | if (found) | |
299 | retval = found->handle.handle; | |
300 | fast_exit: | |
301 | return retval; | |
302 | } | |
c0cfc337 | 303 | EXPORT_SYMBOL_GPL(stack_depot_save); |