// 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, gfp_t alloc_flags)
  {

  	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
  ");
  		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
  ",
  			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

   *

   * Return: The handle of the stack struct stored in depot

   */

  depot_stack_handle_t stack_depot_save(unsigned long *entries,
  				      unsigned int nr_entries,
  				      gfp_t alloc_flags)

  {

  	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 (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(!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, alloc_flags);
  		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);