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Diffstat (limited to 'lib/stackdepot.c')
| -rw-r--r-- | lib/stackdepot.c | 541 |
1 files changed, 541 insertions, 0 deletions
diff --git a/lib/stackdepot.c b/lib/stackdepot.c new file mode 100644 index 0000000000..2f5aa85183 --- /dev/null +++ b/lib/stackdepot.c @@ -0,0 +1,541 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Stack depot - a stack trace storage that avoids duplication. + * + * Internally, stack depot maintains a hash table of unique stacktraces. The + * stack traces themselves are stored contiguously one after another in a set + * of separate page allocations. + * + * Author: Alexander Potapenko <glider@google.com> + * Copyright (C) 2016 Google, Inc. + * + * Based on the code by Dmitry Chernenkov. + */ + +#define pr_fmt(fmt) "stackdepot: " fmt + +#include <linux/gfp.h> +#include <linux/jhash.h> +#include <linux/kernel.h> +#include <linux/kmsan.h> +#include <linux/mm.h> +#include <linux/mutex.h> +#include <linux/percpu.h> +#include <linux/printk.h> +#include <linux/slab.h> +#include <linux/stacktrace.h> +#include <linux/stackdepot.h> +#include <linux/string.h> +#include <linux/types.h> +#include <linux/memblock.h> +#include <linux/kasan-enabled.h> + +#define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8) + +#define DEPOT_VALID_BITS 1 +#define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */ +#define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER)) +#define DEPOT_STACK_ALIGN 4 +#define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN) +#define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_VALID_BITS - \ + DEPOT_OFFSET_BITS - STACK_DEPOT_EXTRA_BITS) +#define DEPOT_POOLS_CAP 8192 +#define DEPOT_MAX_POOLS \ + (((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \ + (1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP) + +/* Compact structure that stores a reference to a stack. */ +union handle_parts { + depot_stack_handle_t handle; + struct { + u32 pool_index : DEPOT_POOL_INDEX_BITS; + u32 offset : DEPOT_OFFSET_BITS; + u32 valid : DEPOT_VALID_BITS; + u32 extra : STACK_DEPOT_EXTRA_BITS; + }; +}; + +struct stack_record { + struct stack_record *next; /* Link in the hash table */ + u32 hash; /* Hash in the hash table */ + u32 size; /* Number of stored frames */ + union handle_parts handle; + unsigned long entries[]; /* Variable-sized array of frames */ +}; + +static bool stack_depot_disabled; +static bool __stack_depot_early_init_requested __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT); +static bool __stack_depot_early_init_passed __initdata; + +/* Use one hash table bucket per 16 KB of memory. */ +#define STACK_HASH_TABLE_SCALE 14 +/* Limit the number of buckets between 4K and 1M. */ +#define STACK_BUCKET_NUMBER_ORDER_MIN 12 +#define STACK_BUCKET_NUMBER_ORDER_MAX 20 +/* Initial seed for jhash2. */ +#define STACK_HASH_SEED 0x9747b28c + +/* Hash table of pointers to stored stack traces. */ +static struct stack_record **stack_table; +/* Fixed order of the number of table buckets. Used when KASAN is enabled. */ +static unsigned int stack_bucket_number_order; +/* Hash mask for indexing the table. */ +static unsigned int stack_hash_mask; + +/* Array of memory regions that store stack traces. */ +static void *stack_pools[DEPOT_MAX_POOLS]; +/* Currently used pool in stack_pools. */ +static int pool_index; +/* Offset to the unused space in the currently used pool. */ +static size_t pool_offset; +/* Lock that protects the variables above. */ +static DEFINE_RAW_SPINLOCK(pool_lock); +/* + * Stack depot tries to keep an extra pool allocated even before it runs out + * of space in the currently used pool. + * This flag marks that this next extra pool needs to be allocated and + * initialized. It has the value 0 when either the next pool is not yet + * initialized or the limit on the number of pools is reached. + */ +static int next_pool_required = 1; + +static int __init disable_stack_depot(char *str) +{ + int ret; + + ret = kstrtobool(str, &stack_depot_disabled); + if (!ret && stack_depot_disabled) { + pr_info("disabled\n"); + stack_table = NULL; + } + return 0; +} +early_param("stack_depot_disable", disable_stack_depot); + +void __init stack_depot_request_early_init(void) +{ + /* Too late to request early init now. */ + WARN_ON(__stack_depot_early_init_passed); + + __stack_depot_early_init_requested = true; +} + +/* Allocates a hash table via memblock. Can only be used during early boot. */ +int __init stack_depot_early_init(void) +{ + unsigned long entries = 0; + + /* This function must be called only once, from mm_init(). */ + if (WARN_ON(__stack_depot_early_init_passed)) + return 0; + __stack_depot_early_init_passed = true; + + /* + * If KASAN is enabled, use the maximum order: KASAN is frequently used + * in fuzzing scenarios, which leads to a large number of different + * stack traces being stored in stack depot. + */ + if (kasan_enabled() && !stack_bucket_number_order) + stack_bucket_number_order = STACK_BUCKET_NUMBER_ORDER_MAX; + + if (!__stack_depot_early_init_requested || stack_depot_disabled) + return 0; + + /* + * If stack_bucket_number_order is not set, leave entries as 0 to rely + * on the automatic calculations performed by alloc_large_system_hash. + */ + if (stack_bucket_number_order) + entries = 1UL << stack_bucket_number_order; + pr_info("allocating hash table via alloc_large_system_hash\n"); + stack_table = alloc_large_system_hash("stackdepot", + sizeof(struct stack_record *), + entries, + STACK_HASH_TABLE_SCALE, + HASH_EARLY | HASH_ZERO, + NULL, + &stack_hash_mask, + 1UL << STACK_BUCKET_NUMBER_ORDER_MIN, + 1UL << STACK_BUCKET_NUMBER_ORDER_MAX); + if (!stack_table) { + pr_err("hash table allocation failed, disabling\n"); + stack_depot_disabled = true; + return -ENOMEM; + } + + return 0; +} + +/* Allocates a hash table via kvcalloc. Can be used after boot. */ +int stack_depot_init(void) +{ + static DEFINE_MUTEX(stack_depot_init_mutex); + unsigned long entries; + int ret = 0; + + mutex_lock(&stack_depot_init_mutex); + + if (stack_depot_disabled || stack_table) + goto out_unlock; + + /* + * Similarly to stack_depot_early_init, use stack_bucket_number_order + * if assigned, and rely on automatic scaling otherwise. + */ + if (stack_bucket_number_order) { + entries = 1UL << stack_bucket_number_order; + } else { + int scale = STACK_HASH_TABLE_SCALE; + + entries = nr_free_buffer_pages(); + entries = roundup_pow_of_two(entries); + + if (scale > PAGE_SHIFT) + entries >>= (scale - PAGE_SHIFT); + else + entries <<= (PAGE_SHIFT - scale); + } + + if (entries < 1UL << STACK_BUCKET_NUMBER_ORDER_MIN) + entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MIN; + if (entries > 1UL << STACK_BUCKET_NUMBER_ORDER_MAX) + entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MAX; + + pr_info("allocating hash table of %lu entries via kvcalloc\n", entries); + stack_table = kvcalloc(entries, sizeof(struct stack_record *), GFP_KERNEL); + if (!stack_table) { + pr_err("hash table allocation failed, disabling\n"); + stack_depot_disabled = true; + ret = -ENOMEM; + goto out_unlock; + } + stack_hash_mask = entries - 1; + +out_unlock: + mutex_unlock(&stack_depot_init_mutex); + + return ret; +} +EXPORT_SYMBOL_GPL(stack_depot_init); + +/* Uses preallocated memory to initialize a new stack depot pool. */ +static void depot_init_pool(void **prealloc) +{ + /* + * If the next pool is already initialized or the maximum number of + * pools is reached, do not use the preallocated memory. + * smp_load_acquire() here pairs with smp_store_release() below and + * in depot_alloc_stack(). + */ + if (!smp_load_acquire(&next_pool_required)) + return; + + /* Check if the current pool is not yet allocated. */ + if (stack_pools[pool_index] == NULL) { + /* Use the preallocated memory for the current pool. */ + stack_pools[pool_index] = *prealloc; + *prealloc = NULL; + } else { + /* + * Otherwise, use the preallocated memory for the next pool + * as long as we do not exceed the maximum number of pools. + */ + if (pool_index + 1 < DEPOT_MAX_POOLS) { + stack_pools[pool_index + 1] = *prealloc; + *prealloc = NULL; + } + /* + * At this point, either the next pool is initialized or the + * maximum number of pools is reached. In either case, take + * note that initializing another pool is not required. + * This smp_store_release pairs with smp_load_acquire() above + * and in stack_depot_save(). + */ + smp_store_release(&next_pool_required, 0); + } +} + +/* Allocates a new stack in a stack depot pool. */ +static struct stack_record * +depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc) +{ + struct stack_record *stack; + size_t required_size = struct_size(stack, entries, size); + + required_size = ALIGN(required_size, 1 << DEPOT_STACK_ALIGN); + + /* Check if there is not enough space in the current pool. */ + if (unlikely(pool_offset + required_size > DEPOT_POOL_SIZE)) { + /* Bail out if we reached the pool limit. */ + if (unlikely(pool_index + 1 >= DEPOT_MAX_POOLS)) { + WARN_ONCE(1, "Stack depot reached limit capacity"); + return NULL; + } + + /* + * Move on to the next pool. + * WRITE_ONCE pairs with potential concurrent read in + * stack_depot_fetch(). + */ + WRITE_ONCE(pool_index, pool_index + 1); + pool_offset = 0; + /* + * If the maximum number of pools is not reached, take note + * that the next pool needs to initialized. + * smp_store_release() here pairs with smp_load_acquire() in + * stack_depot_save() and depot_init_pool(). + */ + if (pool_index + 1 < DEPOT_MAX_POOLS) + smp_store_release(&next_pool_required, 1); + } + + /* Assign the preallocated memory to a pool if required. */ + if (*prealloc) + depot_init_pool(prealloc); + + /* Check if we have a pool to save the stack trace. */ + if (stack_pools[pool_index] == NULL) + return NULL; + + /* Save the stack trace. */ + stack = stack_pools[pool_index] + pool_offset; + stack->hash = hash; + stack->size = size; + stack->handle.pool_index = pool_index; + stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN; + stack->handle.valid = 1; + stack->handle.extra = 0; + memcpy(stack->entries, entries, flex_array_size(stack, entries, size)); + pool_offset += required_size; + /* + * Let KMSAN know the stored stack record is initialized. This shall + * prevent false positive reports if instrumented code accesses it. + */ + kmsan_unpoison_memory(stack, required_size); + + return stack; +} + +/* Calculates the hash for a stack. */ +static inline u32 hash_stack(unsigned long *entries, unsigned int size) +{ + return jhash2((u32 *)entries, + array_size(size, sizeof(*entries)) / sizeof(u32), + STACK_HASH_SEED); +} + +/* + * Non-instrumented version of memcmp(). + * Does not check the lexicographical order, only the equality. + */ +static inline +int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2, + unsigned int n) +{ + for ( ; n-- ; u1++, u2++) { + if (*u1 != *u2) + return 1; + } + return 0; +} + +/* Finds a stack in a bucket of the hash table. */ +static inline struct stack_record *find_stack(struct stack_record *bucket, + unsigned long *entries, int size, + u32 hash) +{ + struct stack_record *found; + + for (found = bucket; found; found = found->next) { + if (found->hash == hash && + found->size == size && + !stackdepot_memcmp(entries, found->entries, size)) + return found; + } + return NULL; +} + +depot_stack_handle_t __stack_depot_save(unsigned long *entries, + unsigned int nr_entries, + gfp_t alloc_flags, bool can_alloc) +{ + struct stack_record *found = NULL, **bucket; + union handle_parts retval = { .handle = 0 }; + struct page *page = NULL; + void *prealloc = NULL; + unsigned long flags; + u32 hash; + + /* + * If this stack trace is from an interrupt, including anything before + * interrupt entry usually leads to unbounded stack depot growth. + * + * Since use of filter_irq_stacks() is a requirement to ensure stack + * depot can efficiently deduplicate interrupt stacks, always + * filter_irq_stacks() to simplify all callers' use of stack depot. + */ + nr_entries = filter_irq_stacks(entries, nr_entries); + + if (unlikely(nr_entries == 0) || stack_depot_disabled) + goto fast_exit; + + hash = hash_stack(entries, nr_entries); + bucket = &stack_table[hash & stack_hash_mask]; + + /* + * Fast path: look the stack trace up without locking. + * The smp_load_acquire() here pairs with smp_store_release() to + * |bucket| below. + */ + found = find_stack(smp_load_acquire(bucket), entries, nr_entries, hash); + if (found) + goto exit; + + /* + * Check if another stack pool needs to be initialized. If so, allocate + * the memory now - we won't be able to do that under the lock. + * + * The smp_load_acquire() here pairs with smp_store_release() to + * |next_pool_inited| in depot_alloc_stack() and depot_init_pool(). + */ + if (unlikely(can_alloc && smp_load_acquire(&next_pool_required))) { + /* + * Zero out zone modifiers, as we don't have specific zone + * requirements. Keep the flags related to allocation in atomic + * contexts and I/O. + */ + alloc_flags &= ~GFP_ZONEMASK; + alloc_flags &= (GFP_ATOMIC | GFP_KERNEL); + alloc_flags |= __GFP_NOWARN; + page = alloc_pages(alloc_flags, DEPOT_POOL_ORDER); + if (page) + prealloc = page_address(page); + } + + raw_spin_lock_irqsave(&pool_lock, flags); + + found = find_stack(*bucket, entries, nr_entries, hash); + if (!found) { + struct stack_record *new = + depot_alloc_stack(entries, nr_entries, hash, &prealloc); + + if (new) { + new->next = *bucket; + /* + * This smp_store_release() pairs with + * smp_load_acquire() from |bucket| above. + */ + smp_store_release(bucket, new); + found = new; + } + } else if (prealloc) { + /* + * Stack depot already contains this stack trace, but let's + * keep the preallocated memory for the future. + */ + depot_init_pool(&prealloc); + } + + raw_spin_unlock_irqrestore(&pool_lock, flags); +exit: + if (prealloc) { + /* Stack depot didn't use this memory, free it. */ + free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER); + } + if (found) + retval.handle = found->handle.handle; +fast_exit: + return retval.handle; +} +EXPORT_SYMBOL_GPL(__stack_depot_save); + +depot_stack_handle_t stack_depot_save(unsigned long *entries, + unsigned int nr_entries, + gfp_t alloc_flags) +{ + return __stack_depot_save(entries, nr_entries, alloc_flags, true); +} +EXPORT_SYMBOL_GPL(stack_depot_save); + +unsigned int stack_depot_fetch(depot_stack_handle_t handle, + unsigned long **entries) +{ + union handle_parts parts = { .handle = handle }; + /* + * READ_ONCE pairs with potential concurrent write in + * depot_alloc_stack. + */ + int pool_index_cached = READ_ONCE(pool_index); + void *pool; + size_t offset = parts.offset << DEPOT_STACK_ALIGN; + struct stack_record *stack; + + *entries = NULL; + /* + * Let KMSAN know *entries is initialized. This shall prevent false + * positive reports if instrumented code accesses it. + */ + kmsan_unpoison_memory(entries, sizeof(*entries)); + + if (!handle) + return 0; + + if (parts.pool_index > pool_index_cached) { + WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n", + parts.pool_index, pool_index_cached, handle); + return 0; + } + pool = stack_pools[parts.pool_index]; + if (!pool) + return 0; + stack = pool + offset; + + *entries = stack->entries; + return stack->size; +} +EXPORT_SYMBOL_GPL(stack_depot_fetch); + +void stack_depot_print(depot_stack_handle_t stack) +{ + unsigned long *entries; + unsigned int nr_entries; + + nr_entries = stack_depot_fetch(stack, &entries); + if (nr_entries > 0) + stack_trace_print(entries, nr_entries, 0); +} +EXPORT_SYMBOL_GPL(stack_depot_print); + +int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size, + int spaces) +{ + unsigned long *entries; + unsigned int nr_entries; + + nr_entries = stack_depot_fetch(handle, &entries); + return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries, + spaces) : 0; +} +EXPORT_SYMBOL_GPL(stack_depot_snprint); + +depot_stack_handle_t __must_check stack_depot_set_extra_bits( + depot_stack_handle_t handle, unsigned int extra_bits) +{ + union handle_parts parts = { .handle = handle }; + + /* Don't set extra bits on empty handles. */ + if (!handle) + return 0; + + parts.extra = extra_bits; + return parts.handle; +} +EXPORT_SYMBOL(stack_depot_set_extra_bits); + +unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle) +{ + union handle_parts parts = { .handle = handle }; + + return parts.extra; +} +EXPORT_SYMBOL(stack_depot_get_extra_bits); |