| // SPDX-License-Identifier: GPL-2.0-only |
| /* |
| * Generic stack depot for storing stack traces. |
| * |
| * Some debugging tools need to save stack traces of certain events which can |
| * be later presented to the user. For example, KASAN needs to safe alloc and |
| * free stacks for each object, but storing two stack traces per object |
| * requires too much memory (e.g. SLUB_DEBUG needs 256 bytes per object for |
| * that). |
| * |
| * Instead, stack depot maintains a hashtable of unique stacktraces. Since alloc |
| * and free stacks repeat a lot, we save about 100x space. |
| * Stacks are never removed from depot, so we store them contiguously one after |
| * another in a contiguous memory allocation. |
| * |
| * Author: Alexander Potapenko <glider@google.com> |
| * Copyright (C) 2016 Google, Inc. |
| * |
| * Based on code by Dmitry Chernenkov. |
| */ |
| |
| #include <linux/gfp.h> |
| #include <linux/jhash.h> |
| #include <linux/kernel.h> |
| #include <linux/mm.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> |
| |
| #define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8) |
| |
| #define STACK_ALLOC_NULL_PROTECTION_BITS 1 |
| #define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */ |
| #define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER)) |
| #define STACK_ALLOC_ALIGN 4 |
| #define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \ |
| STACK_ALLOC_ALIGN) |
| #define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \ |
| STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS) |
| #define STACK_ALLOC_SLABS_CAP 8192 |
| #define STACK_ALLOC_MAX_SLABS \ |
| (((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \ |
| (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP) |
| |
| /* The compact structure to store the reference to stacks. */ |
| union handle_parts { |
| depot_stack_handle_t handle; |
| struct { |
| u32 slabindex : STACK_ALLOC_INDEX_BITS; |
| u32 offset : STACK_ALLOC_OFFSET_BITS; |
| u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS; |
| }; |
| }; |
| |
| struct stack_record { |
| struct stack_record *next; /* Link in the hashtable */ |
| u32 hash; /* Hash in the hastable */ |
| u32 size; /* Number of frames in the stack */ |
| union handle_parts handle; |
| unsigned long entries[]; /* Variable-sized array of entries. */ |
| }; |
| |
| static void *stack_slabs[STACK_ALLOC_MAX_SLABS]; |
| |
| static int depot_index; |
| static int next_slab_inited; |
| static size_t depot_offset; |
| static DEFINE_RAW_SPINLOCK(depot_lock); |
| |
| static bool init_stack_slab(void **prealloc) |
| { |
| if (!*prealloc) |
| return false; |
| /* |
| * This smp_load_acquire() pairs with smp_store_release() to |
| * |next_slab_inited| below and in depot_alloc_stack(). |
| */ |
| if (smp_load_acquire(&next_slab_inited)) |
| return true; |
| if (stack_slabs[depot_index] == NULL) { |
| stack_slabs[depot_index] = *prealloc; |
| *prealloc = NULL; |
| } else { |
| /* If this is the last depot slab, do not touch the next one. */ |
| if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) { |
| stack_slabs[depot_index + 1] = *prealloc; |
| *prealloc = NULL; |
| } |
| /* |
| * This smp_store_release pairs with smp_load_acquire() from |
| * |next_slab_inited| above and in stack_depot_save(). |
| */ |
| smp_store_release(&next_slab_inited, 1); |
| } |
| return true; |
| } |
| |
| /* Allocation of a new stack in raw storage */ |
| 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 << STACK_ALLOC_ALIGN); |
| |
| if (unlikely(depot_offset + required_size > STACK_ALLOC_SIZE)) { |
| if (unlikely(depot_index + 1 >= STACK_ALLOC_MAX_SLABS)) { |
| WARN_ONCE(1, "Stack depot reached limit capacity"); |
| return NULL; |
| } |
| depot_index++; |
| depot_offset = 0; |
| /* |
| * smp_store_release() here pairs with smp_load_acquire() from |
| * |next_slab_inited| in stack_depot_save() and |
| * init_stack_slab(). |
| */ |
| if (depot_index + 1 < STACK_ALLOC_MAX_SLABS) |
| smp_store_release(&next_slab_inited, 0); |
| } |
| init_stack_slab(prealloc); |
| if (stack_slabs[depot_index] == NULL) |
| return NULL; |
| |
| stack = stack_slabs[depot_index] + depot_offset; |
| |
| stack->hash = hash; |
| stack->size = size; |
| stack->handle.slabindex = depot_index; |
| stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN; |
| stack->handle.valid = 1; |
| memcpy(stack->entries, entries, flex_array_size(stack, entries, size)); |
| depot_offset += required_size; |
| |
| return stack; |
| } |
| |
| #define STACK_HASH_SIZE (1L << CONFIG_STACK_HASH_ORDER) |
| #define STACK_HASH_MASK (STACK_HASH_SIZE - 1) |
| #define STACK_HASH_SEED 0x9747b28c |
| |
| static bool stack_depot_disable; |
| static struct stack_record **stack_table; |
| |
| static int __init is_stack_depot_disabled(char *str) |
| { |
| int ret; |
| |
| ret = kstrtobool(str, &stack_depot_disable); |
| if (!ret && stack_depot_disable) { |
| pr_info("Stack Depot is disabled\n"); |
| stack_table = NULL; |
| } |
| return 0; |
| } |
| early_param("stack_depot_disable", is_stack_depot_disabled); |
| |
| int __init stack_depot_init(void) |
| { |
| if (!stack_depot_disable) { |
| size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *)); |
| int i; |
| |
| stack_table = memblock_alloc(size, size); |
| for (i = 0; i < STACK_HASH_SIZE; i++) |
| stack_table[i] = NULL; |
| } |
| return 0; |
| } |
| |
| /* Calculate 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); |
| } |
| |
| /* Use our own, non-instrumented version of memcmp(). |
| * |
| * We actually don't care about the order, just 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; |
| } |
| |
| /* Find a stack that is equal to the one stored in entries in the hash */ |
| 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; |
| } |
| |
| /** |
| * stack_depot_fetch - Fetch stack entries from a depot |
| * |
| * @handle: Stack depot handle which was returned from |
| * stack_depot_save(). |
| * @entries: Pointer to store the entries address |
| * |
| * Return: The number of trace entries for this depot. |
| */ |
| unsigned int stack_depot_fetch(depot_stack_handle_t handle, |
| unsigned long **entries) |
| { |
| union handle_parts parts = { .handle = handle }; |
| void *slab; |
| size_t offset = parts.offset << STACK_ALLOC_ALIGN; |
| struct stack_record *stack; |
| |
| *entries = NULL; |
| if (parts.slabindex > depot_index) { |
| WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n", |
| parts.slabindex, depot_index, handle); |
| return 0; |
| } |
| slab = stack_slabs[parts.slabindex]; |
| if (!slab) |
| return 0; |
| stack = slab + offset; |
| |
| *entries = stack->entries; |
| return stack->size; |
| } |
| EXPORT_SYMBOL_GPL(stack_depot_fetch); |
| |
| /** |
| * __stack_depot_save - Save a stack trace from an array |
| * |
| * @entries: Pointer to storage array |
| * @nr_entries: Size of the storage array |
| * @alloc_flags: Allocation gfp flags |
| * @can_alloc: Allocate stack slabs (increased chance of failure if false) |
| * |
| * Saves a stack trace from @entries array of size @nr_entries. If @can_alloc is |
| * %true, is allowed to replenish the stack slab pool in case no space is left |
| * (allocates using GFP flags of @alloc_flags). If @can_alloc is %false, avoids |
| * any allocations and will fail if no space is left to store the stack trace. |
| * |
| * If the stack trace in @entries is from an interrupt, only the portion up to |
| * interrupt entry is saved. |
| * |
| * Context: Any context, but setting @can_alloc to %false is required if |
| * alloc_pages() cannot be used from the current context. Currently |
| * this is the case from contexts where neither %GFP_ATOMIC nor |
| * %GFP_NOWAIT can be used (NMI, raw_spin_lock). |
| * |
| * Return: The handle of the stack struct stored in depot, 0 on failure. |
| */ |
| 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; |
| depot_stack_handle_t retval = 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 stackdepot growth. |
| * |
| * Because use of filter_irq_stacks() is a requirement to ensure |
| * stackdepot can efficiently deduplicate interrupt stacks, always |
| * filter_irq_stacks() to simplify all callers' use of stackdepot. |
| */ |
| nr_entries = filter_irq_stacks(entries, nr_entries); |
| |
| if (unlikely(nr_entries == 0) || stack_depot_disable) |
| 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 the current or the next stack slab need to be initialized. |
| * If so, allocate the memory - we won't be able to do that under the |
| * lock. |
| * |
| * The smp_load_acquire() here pairs with smp_store_release() to |
| * |next_slab_inited| in depot_alloc_stack() and init_stack_slab(). |
| */ |
| if (unlikely(can_alloc && !smp_load_acquire(&next_slab_inited))) { |
| /* |
| * 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, STACK_ALLOC_ORDER); |
| if (page) |
| prealloc = page_address(page); |
| } |
| |
| raw_spin_lock_irqsave(&depot_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) { |
| /* |
| * We didn't need to store this stack trace, but let's keep |
| * the preallocated memory for the future. |
| */ |
| WARN_ON(!init_stack_slab(&prealloc)); |
| } |
| |
| raw_spin_unlock_irqrestore(&depot_lock, flags); |
| exit: |
| if (prealloc) { |
| /* Nobody used this memory, ok to free it. */ |
| free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER); |
| } |
| if (found) |
| retval = found->handle.handle; |
| fast_exit: |
| return retval; |
| } |
| EXPORT_SYMBOL_GPL(__stack_depot_save); |
| |
| /** |
| * stack_depot_save - Save a stack trace from an array |
| * |
| * @entries: Pointer to storage array |
| * @nr_entries: Size of the storage array |
| * @alloc_flags: Allocation gfp flags |
| * |
| * Context: Contexts where allocations via alloc_pages() are allowed. |
| * See __stack_depot_save() for more details. |
| * |
| * Return: The handle of the stack struct stored in depot, 0 on failure. |
| */ |
| 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); |