Merge tag 'vfio-v6.0-rc5' of https://github.com/awilliam/linux-vfio

[people/ms/linux.git] / lib / stackdepot.c

// 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/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_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 bool __stack_depot_want_early_init __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
static bool __stack_depot_early_init_passed __initdata;

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;
}

/* one hash table bucket entry per 16kB of memory */
#define STACK_HASH_SCALE        14
/* limited between 4k and 1M buckets */
#define STACK_HASH_ORDER_MIN    12
#define STACK_HASH_ORDER_MAX    20
#define STACK_HASH_SEED 0x9747b28c

static unsigned int stack_hash_order;
static unsigned int stack_hash_mask;

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);

void __init stack_depot_want_early_init(void)
{
        /* Too late to request early init now */
        WARN_ON(__stack_depot_early_init_passed);

        __stack_depot_want_early_init = true;
}

int __init stack_depot_early_init(void)
{
        unsigned long entries = 0;

        /* This is supposed to 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_enabled() && !stack_hash_order)
                stack_hash_order = STACK_HASH_ORDER_MAX;

        if (!__stack_depot_want_early_init || stack_depot_disable)
                return 0;

        if (stack_hash_order)
                entries = 1UL <<  stack_hash_order;
        stack_table = alloc_large_system_hash("stackdepot",
                                                sizeof(struct stack_record *),
                                                entries,
                                                STACK_HASH_SCALE,
                                                HASH_EARLY | HASH_ZERO,
                                                NULL,
                                                &stack_hash_mask,
                                                1UL << STACK_HASH_ORDER_MIN,
                                                1UL << STACK_HASH_ORDER_MAX);

        if (!stack_table) {
                pr_err("Stack Depot hash table allocation failed, disabling\n");
                stack_depot_disable = true;
                return -ENOMEM;
        }

        return 0;
}

int stack_depot_init(void)
{
        static DEFINE_MUTEX(stack_depot_init_mutex);
        int ret = 0;

        mutex_lock(&stack_depot_init_mutex);
        if (!stack_depot_disable && !stack_table) {
                unsigned long entries;
                int scale = STACK_HASH_SCALE;

                if (stack_hash_order) {
                        entries = 1UL << stack_hash_order;
                } else {
                        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_HASH_ORDER_MIN)
                        entries = 1UL << STACK_HASH_ORDER_MIN;
                if (entries > 1UL << STACK_HASH_ORDER_MAX)
                        entries = 1UL << STACK_HASH_ORDER_MAX;

                pr_info("Stack Depot allocating hash table of %lu entries with kvcalloc\n",
                                entries);
                stack_table = kvcalloc(entries, sizeof(struct stack_record *), GFP_KERNEL);
                if (!stack_table) {
                        pr_err("Stack Depot hash table allocation failed, disabling\n");
                        stack_depot_disable = true;
                        ret = -ENOMEM;
                }
                stack_hash_mask = entries - 1;
        }
        mutex_unlock(&stack_depot_init_mutex);
        return ret;
}
EXPORT_SYMBOL_GPL(stack_depot_init);

/* 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_snprint - print stack entries from a depot into a buffer
 *
 * @handle:     Stack depot handle which was returned from
 *              stack_depot_save().
 * @buf:        Pointer to the print buffer
 *
 * @size:       Size of the print buffer
 *
 * @spaces:     Number of leading spaces to print
 *
 * Return:      Number of bytes printed.
 */
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);

/**
 * stack_depot_print - print stack entries from a depot
 *
 * @stack:              Stack depot handle which was returned from
 *                      stack_depot_save().
 *
 */
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);

/**
 * 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 (!handle)
                return 0;

        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);