1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /*
3 * Stack depot - a stack trace storage that avoids duplication.
4 *
5 * Stack depot is intended to be used by subsystems that need to store and
6 * later retrieve many potentially duplicated stack traces without wasting
7 * memory.
8 *
9 * For example, KASAN needs to save allocation and free stack traces for each
10 * object. Storing two stack traces per object requires a lot of memory (e.g.
11 * SLUB_DEBUG needs 256 bytes per object for that). Since allocation and free
12 * stack traces often repeat, using stack depot allows to save about 100x space.
13 *
14 * Author: Alexander Potapenko <glider@google.com>
15 * Copyright (C) 2016 Google, Inc.
16 *
17 * Based on the code by Dmitry Chernenkov.
18 */
19
20 #ifndef _LINUX_STACKDEPOT_H
21 #define _LINUX_STACKDEPOT_H
22
23 #include <linux/gfp.h>
24
25 typedef u32 depot_stack_handle_t;
26
27 /*
28 * Number of bits in the handle that stack depot doesn't use. Users may store
29 * information in them via stack_depot_set/get_extra_bits.
30 */
31 #define STACK_DEPOT_EXTRA_BITS 5
32
33 #define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)
34
35 #define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */
36 #define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER))
37 #define DEPOT_STACK_ALIGN 4
38 #define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
39 #define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \
40 STACK_DEPOT_EXTRA_BITS)
41
42 #ifdef CONFIG_STACKDEPOT
43 /* Compact structure that stores a reference to a stack. */
44 union handle_parts {
45 depot_stack_handle_t handle;
46 struct {
47 u32 pool_index_plus_1 : DEPOT_POOL_INDEX_BITS;
48 u32 offset : DEPOT_OFFSET_BITS;
49 u32 extra : STACK_DEPOT_EXTRA_BITS;
50 };
51 };
52
53 struct stack_record {
54 struct list_head hash_list; /* Links in the hash table */
55 u32 hash; /* Hash in hash table */
56 u32 size; /* Number of stored frames */
57 union handle_parts handle; /* Constant after initialization */
58 refcount_t count;
59 union {
60 unsigned long entries[CONFIG_STACKDEPOT_MAX_FRAMES]; /* Frames */
61 struct {
62 /*
63 * An important invariant of the implementation is to
64 * only place a stack record onto the freelist iff its
65 * refcount is zero. Because stack records with a zero
66 * refcount are never considered as valid, it is safe to
67 * union @entries and freelist management state below.
68 * Conversely, as soon as an entry is off the freelist
69 * and its refcount becomes non-zero, the below must not
70 * be accessed until being placed back on the freelist.
71 */
72 struct list_head free_list; /* Links in the freelist */
73 unsigned long rcu_state; /* RCU cookie */
74 };
75 };
76 };
77 #endif
78
79 typedef u32 depot_flags_t;
80
81 /*
82 * Flags that can be passed to stack_depot_save_flags(); see the comment next
83 * to its declaration for more details.
84 */
85 #define STACK_DEPOT_FLAG_CAN_ALLOC ((depot_flags_t)0x0001)
86 #define STACK_DEPOT_FLAG_GET ((depot_flags_t)0x0002)
87
88 #define STACK_DEPOT_FLAGS_NUM 2
89 #define STACK_DEPOT_FLAGS_MASK ((depot_flags_t)((1 << STACK_DEPOT_FLAGS_NUM) - 1))
90
91 /*
92 * Using stack depot requires its initialization, which can be done in 3 ways:
93 *
94 * 1. Selecting CONFIG_STACKDEPOT_ALWAYS_INIT. This option is suitable in
95 * scenarios where it's known at compile time that stack depot will be used.
96 * Enabling this config makes the kernel initialize stack depot in mm_init().
97 *
98 * 2. Calling stack_depot_request_early_init() during early boot, before
99 * stack_depot_early_init() in mm_init() completes. For example, this can
100 * be done when evaluating kernel boot parameters.
101 *
102 * 3. Calling stack_depot_init(). Possible after boot is complete. This option
103 * is recommended for modules initialized later in the boot process, after
104 * mm_init() completes.
105 *
106 * stack_depot_init() and stack_depot_request_early_init() can be called
107 * regardless of whether CONFIG_STACKDEPOT is enabled and are no-op when this
108 * config is disabled. The save/fetch/print stack depot functions can only be
109 * called from the code that makes sure CONFIG_STACKDEPOT is enabled _and_
110 * initializes stack depot via one of the ways listed above.
111 */
112 #ifdef CONFIG_STACKDEPOT
113 int stack_depot_init(void);
114
115 void __init stack_depot_request_early_init(void);
116
117 /* Must be only called from mm_init(). */
118 int __init stack_depot_early_init(void);
119 #else
120 static inline int stack_depot_init(void) { return 0; }
121
122 static inline void stack_depot_request_early_init(void) { }
123
124 static inline int stack_depot_early_init(void) { return 0; }
125 #endif
126
127 /**
128 * stack_depot_save_flags - Save a stack trace to stack depot
129 *
130 * @entries: Pointer to the stack trace
131 * @nr_entries: Number of frames in the stack
132 * @alloc_flags: Allocation GFP flags
133 * @depot_flags: Stack depot flags
134 *
135 * Saves a stack trace from @entries array of size @nr_entries.
136 *
137 * If STACK_DEPOT_FLAG_CAN_ALLOC is set in @depot_flags, stack depot can
138 * replenish the stack pools in case no space is left (allocates using GFP
139 * flags of @alloc_flags). Otherwise, stack depot avoids any allocations and
140 * fails if no space is left to store the stack trace.
141 *
142 * If STACK_DEPOT_FLAG_GET is set in @depot_flags, stack depot will increment
143 * the refcount on the saved stack trace if it already exists in stack depot.
144 * Users of this flag must also call stack_depot_put() when keeping the stack
145 * trace is no longer required to avoid overflowing the refcount.
146 *
147 * If the provided stack trace comes from the interrupt context, only the part
148 * up to the interrupt entry is saved.
149 *
150 * Context: Any context, but setting STACK_DEPOT_FLAG_CAN_ALLOC is required if
151 * alloc_pages() cannot be used from the current context. Currently
152 * this is the case for contexts where neither %GFP_ATOMIC nor
153 * %GFP_NOWAIT can be used (NMI, raw_spin_lock).
154 *
155 * Return: Handle of the stack struct stored in depot, 0 on failure
156 */
157 depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
158 unsigned int nr_entries,
159 gfp_t gfp_flags,
160 depot_flags_t depot_flags);
161
162 /**
163 * stack_depot_save - Save a stack trace to stack depot
164 *
165 * @entries: Pointer to the stack trace
166 * @nr_entries: Number of frames in the stack
167 * @alloc_flags: Allocation GFP flags
168 *
169 * Does not increment the refcount on the saved stack trace; see
170 * stack_depot_save_flags() for more details.
171 *
172 * Context: Contexts where allocations via alloc_pages() are allowed;
173 * see stack_depot_save_flags() for more details.
174 *
175 * Return: Handle of the stack trace stored in depot, 0 on failure
176 */
177 depot_stack_handle_t stack_depot_save(unsigned long *entries,
178 unsigned int nr_entries, gfp_t gfp_flags);
179
180 /**
181 * __stack_depot_get_stack_record - Get a pointer to a stack_record struct
182 *
183 * @handle: Stack depot handle
184 *
185 * This function is only for internal purposes.
186 *
187 * Return: Returns a pointer to a stack_record struct
188 */
189 struct stack_record *__stack_depot_get_stack_record(depot_stack_handle_t handle);
190
191 /**
192 * stack_depot_fetch - Fetch a stack trace from stack depot
193 *
194 * @handle: Stack depot handle returned from stack_depot_save()
195 * @entries: Pointer to store the address of the stack trace
196 *
197 * Return: Number of frames for the fetched stack
198 */
199 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
200 unsigned long **entries);
201
202 /**
203 * stack_depot_print - Print a stack trace from stack depot
204 *
205 * @stack: Stack depot handle returned from stack_depot_save()
206 */
207 void stack_depot_print(depot_stack_handle_t stack);
208
209 /**
210 * stack_depot_snprint - Print a stack trace from stack depot into a buffer
211 *
212 * @handle: Stack depot handle returned from stack_depot_save()
213 * @buf: Pointer to the print buffer
214 * @size: Size of the print buffer
215 * @spaces: Number of leading spaces to print
216 *
217 * Return: Number of bytes printed
218 */
219 int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
220 int spaces);
221
222 /**
223 * stack_depot_put - Drop a reference to a stack trace from stack depot
224 *
225 * @handle: Stack depot handle returned from stack_depot_save()
226 *
227 * The stack trace is evicted from stack depot once all references to it have
228 * been dropped (once the number of stack_depot_evict() calls matches the
229 * number of stack_depot_save_flags() calls with STACK_DEPOT_FLAG_GET set for
230 * this stack trace).
231 */
232 void stack_depot_put(depot_stack_handle_t handle);
233
234 /**
235 * stack_depot_set_extra_bits - Set extra bits in a stack depot handle
236 *
237 * @handle: Stack depot handle returned from stack_depot_save()
238 * @extra_bits: Value to set the extra bits
239 *
240 * Return: Stack depot handle with extra bits set
241 *
242 * Stack depot handles have a few unused bits, which can be used for storing
243 * user-specific information. These bits are transparent to the stack depot.
244 */
245 depot_stack_handle_t __must_check stack_depot_set_extra_bits(
246 depot_stack_handle_t handle, unsigned int extra_bits);
247
248 /**
249 * stack_depot_get_extra_bits - Retrieve extra bits from a stack depot handle
250 *
251 * @handle: Stack depot handle with extra bits saved
252 *
253 * Return: Extra bits retrieved from the stack depot handle
254 */
255 unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle);
256
257 #endif
258
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