lib/stackdepot.c

   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. */
  52 union 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
  61 struct 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
  69 static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
  70
  71 static int depot_index;
  72 static int next_slab_inited;
  73 static size_t depot_offset;
  74 static DEFINE_RAW_SPINLOCK(depot_lock);
  75
  76 static 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 */
 105 static 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
 149 static bool stack_depot_disable;
 150 static struct stack_record **stack_table;
 151
 152 static 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 }
 163 early_param("stack_depot_disable", is_stack_depot_disabled);
 164
 165 int __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 */
 179 static 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  */
 190 static inline
 191 int 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 */
 202 static 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  */
 226 unsigned 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 }
 248 EXPORT_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  */
 259 depot_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);
 333 exit:
 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;
 340 fast_exit:
 341         return retval;
 342 }
 343 EXPORT_SYMBOL_GPL(stack_depot_save);
 344
 345 static 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
 353 unsigned 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 }
 366 EXPORT_SYMBOL_GPL(filter_irq_stacks);