linux/lib/stackdepot.c
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   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#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. */
  52union 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
  61struct 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
  69static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
  70
  71static int depot_index;
  72static int next_slab_inited;
  73static size_t depot_offset;
  74static DEFINE_RAW_SPINLOCK(depot_lock);
  75
  76static 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 */
 105static 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
 149static bool stack_depot_disable;
 150static struct stack_record **stack_table;
 151
 152static 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}
 163early_param("stack_depot_disable", is_stack_depot_disabled);
 164
 165int __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 */
 179static 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 */
 190static inline
 191int 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 */
 202static 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 */
 226unsigned 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}
 248EXPORT_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 */
 259depot_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);
 333exit:
 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;
 340fast_exit:
 341        return retval;
 342}
 343EXPORT_SYMBOL_GPL(stack_depot_save);
 344
 345static 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
 353unsigned 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}
 366EXPORT_SYMBOL_GPL(filter_irq_stacks);
 367