// SPDX-License-Identifier: GPL-2.0

  /*
   * KASAN quarantine.
   *
   * Author: Alexander Potapenko <glider@google.com>
   * Copyright (C) 2016 Google, Inc.
   *
   * Based on code by Dmitry Chernenkov.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * version 2 as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   */
  
  #include <linux/gfp.h>
  #include <linux/hash.h>
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/percpu.h>
  #include <linux/printk.h>
  #include <linux/shrinker.h>
  #include <linux/slab.h>

  #include <linux/srcu.h>

  #include <linux/string.h>
  #include <linux/types.h>

  #include <linux/cpuhotplug.h>

  
  #include "../slab.h"
  #include "kasan.h"
  
  /* Data structure and operations for quarantine queues. */
  
  /*
   * Each queue is a signle-linked list, which also stores the total size of
   * objects inside of it.
   */
  struct qlist_head {
  	struct qlist_node *head;
  	struct qlist_node *tail;
  	size_t bytes;

  	bool offline;

  };
  
  #define QLIST_INIT { NULL, NULL, 0 }
  
  static bool qlist_empty(struct qlist_head *q)
  {
  	return !q->head;
  }
  
  static void qlist_init(struct qlist_head *q)
  {
  	q->head = q->tail = NULL;
  	q->bytes = 0;
  }
  
  static void qlist_put(struct qlist_head *q, struct qlist_node *qlink,
  		size_t size)
  {
  	if (unlikely(qlist_empty(q)))
  		q->head = qlink;
  	else
  		q->tail->next = qlink;
  	q->tail = qlink;
  	qlink->next = NULL;
  	q->bytes += size;
  }
  
  static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
  {
  	if (unlikely(qlist_empty(from)))
  		return;
  
  	if (qlist_empty(to)) {
  		*to = *from;
  		qlist_init(from);
  		return;
  	}
  
  	to->tail->next = from->head;
  	to->tail = from->tail;
  	to->bytes += from->bytes;
  
  	qlist_init(from);
  }

  #define QUARANTINE_PERCPU_SIZE (1 << 20)
  #define QUARANTINE_BATCHES \
  	(1024 > 4 * CONFIG_NR_CPUS ? 1024 : 4 * CONFIG_NR_CPUS)

  
  /*
   * The object quarantine consists of per-cpu queues and a global queue,
   * guarded by quarantine_lock.
   */
  static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);

  /* Round-robin FIFO array of batches. */
  static struct qlist_head global_quarantine[QUARANTINE_BATCHES];
  static int quarantine_head;
  static int quarantine_tail;
  /* Total size of all objects in global_quarantine across all batches. */
  static unsigned long quarantine_size;

  static DEFINE_RAW_SPINLOCK(quarantine_lock);

  DEFINE_STATIC_SRCU(remove_cache_srcu);

  
  /* Maximum size of the global queue. */

  static unsigned long quarantine_max_size;
  
  /*
   * Target size of a batch in global_quarantine.
   * Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM.
   */
  static unsigned long quarantine_batch_size;

  
  /*
   * The fraction of physical memory the quarantine is allowed to occupy.
   * Quarantine doesn't support memory shrinker with SLAB allocator, so we keep
   * the ratio low to avoid OOM.
   */
  #define QUARANTINE_FRACTION 32

  static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
  {
  	return virt_to_head_page(qlink)->slab_cache;
  }
  
  static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
  {
  	struct kasan_free_meta *free_info =
  		container_of(qlink, struct kasan_free_meta,
  			     quarantine_link);
  
  	return ((void *)free_info) - cache->kasan_info.free_meta_offset;
  }
  
  static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
  {
  	void *object = qlink_to_object(qlink, cache);

  	unsigned long flags;

  	if (IS_ENABLED(CONFIG_SLAB))
  		local_irq_save(flags);

  	*(u8 *)kasan_mem_to_shadow(object) = KASAN_KMALLOC_FREE;

  	___cache_free(cache, object, _THIS_IP_);

  
  	if (IS_ENABLED(CONFIG_SLAB))
  		local_irq_restore(flags);

  }
  
  static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
  {
  	struct qlist_node *qlink;
  
  	if (unlikely(qlist_empty(q)))
  		return;
  
  	qlink = q->head;
  	while (qlink) {
  		struct kmem_cache *obj_cache =
  			cache ? cache :	qlink_to_cache(qlink);
  		struct qlist_node *next = qlink->next;
  
  		qlink_free(qlink, obj_cache);
  		qlink = next;
  	}
  	qlist_init(q);
  }
  
  void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
  {
  	unsigned long flags;
  	struct qlist_head *q;
  	struct qlist_head temp = QLIST_INIT;

  	/*
  	 * Note: irq must be disabled until after we move the batch to the
  	 * global quarantine. Otherwise quarantine_remove_cache() can miss
  	 * some objects belonging to the cache if they are in our local temp
  	 * list. quarantine_remove_cache() executes on_each_cpu() at the
  	 * beginning which ensures that it either sees the objects in per-cpu
  	 * lists or in the global quarantine.
  	 */

  	local_irq_save(flags);
  
  	q = this_cpu_ptr(&cpu_quarantine);

  	if (q->offline) {
  		local_irq_restore(flags);
  		return;
  	}

  	qlist_put(q, &info->quarantine_link, cache->size);

  	if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {

  		qlist_move_all(q, &temp);

  		raw_spin_lock(&quarantine_lock);

  		WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
  		qlist_move_all(&temp, &global_quarantine[quarantine_tail]);
  		if (global_quarantine[quarantine_tail].bytes >=
  				READ_ONCE(quarantine_batch_size)) {
  			int new_tail;
  
  			new_tail = quarantine_tail + 1;
  			if (new_tail == QUARANTINE_BATCHES)
  				new_tail = 0;
  			if (new_tail != quarantine_head)
  				quarantine_tail = new_tail;
  		}

  		raw_spin_unlock(&quarantine_lock);

  	}

  
  	local_irq_restore(flags);

  }
  
  void quarantine_reduce(void)
  {

  	size_t total_size, new_quarantine_size, percpu_quarantines;

  	unsigned long flags;

  	int srcu_idx;

  	struct qlist_head to_free = QLIST_INIT;

  	if (likely(READ_ONCE(quarantine_size) <=
  		   READ_ONCE(quarantine_max_size)))

  		return;

  	/*
  	 * srcu critical section ensures that quarantine_remove_cache()
  	 * will not miss objects belonging to the cache while they are in our
  	 * local to_free list. srcu is chosen because (1) it gives us private
  	 * grace period domain that does not interfere with anything else,
  	 * and (2) it allows synchronize_srcu() to return without waiting
  	 * if there are no pending read critical sections (which is the
  	 * expected case).
  	 */
  	srcu_idx = srcu_read_lock(&remove_cache_srcu);

  	raw_spin_lock_irqsave(&quarantine_lock, flags);

  
  	/*
  	 * Update quarantine size in case of hotplug. Allocate a fraction of
  	 * the installed memory to quarantine minus per-cpu queue limits.
  	 */

  	total_size = (totalram_pages() << PAGE_SHIFT) /

  		QUARANTINE_FRACTION;

  	percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();

  	new_quarantine_size = (total_size < percpu_quarantines) ?
  		0 : total_size - percpu_quarantines;
  	WRITE_ONCE(quarantine_max_size, new_quarantine_size);
  	/* Aim at consuming at most 1/2 of slots in quarantine. */
  	WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE,
  		2 * total_size / QUARANTINE_BATCHES));
  
  	if (likely(quarantine_size > quarantine_max_size)) {
  		qlist_move_all(&global_quarantine[quarantine_head], &to_free);
  		WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes);
  		quarantine_head++;
  		if (quarantine_head == QUARANTINE_BATCHES)
  			quarantine_head = 0;

  	}

  	raw_spin_unlock_irqrestore(&quarantine_lock, flags);

  
  	qlist_free_all(&to_free, NULL);

  	srcu_read_unlock(&remove_cache_srcu, srcu_idx);

  }
  
  static void qlist_move_cache(struct qlist_head *from,
  				   struct qlist_head *to,
  				   struct kmem_cache *cache)
  {

  	struct qlist_node *curr;

  
  	if (unlikely(qlist_empty(from)))
  		return;
  
  	curr = from->head;

  	qlist_init(from);

  	while (curr) {

  		struct qlist_node *next = curr->next;
  		struct kmem_cache *obj_cache = qlink_to_cache(curr);
  
  		if (obj_cache == cache)
  			qlist_put(to, curr, obj_cache->size);
  		else
  			qlist_put(from, curr, obj_cache->size);
  
  		curr = next;

  	}
  }
  
  static void per_cpu_remove_cache(void *arg)
  {
  	struct kmem_cache *cache = arg;
  	struct qlist_head to_free = QLIST_INIT;
  	struct qlist_head *q;
  
  	q = this_cpu_ptr(&cpu_quarantine);
  	qlist_move_cache(q, &to_free, cache);
  	qlist_free_all(&to_free, cache);
  }

  /* Free all quarantined objects belonging to cache. */

  void quarantine_remove_cache(struct kmem_cache *cache)
  {

  	unsigned long flags, i;

  	struct qlist_head to_free = QLIST_INIT;

  	/*
  	 * Must be careful to not miss any objects that are being moved from
  	 * per-cpu list to the global quarantine in quarantine_put(),
  	 * nor objects being freed in quarantine_reduce(). on_each_cpu()
  	 * achieves the first goal, while synchronize_srcu() achieves the
  	 * second.
  	 */

  	on_each_cpu(per_cpu_remove_cache, cache, 1);

  	raw_spin_lock_irqsave(&quarantine_lock, flags);

  	for (i = 0; i < QUARANTINE_BATCHES; i++) {
  		if (qlist_empty(&global_quarantine[i]))
  			continue;

  		qlist_move_cache(&global_quarantine[i], &to_free, cache);

  		/* Scanning whole quarantine can take a while. */

  		raw_spin_unlock_irqrestore(&quarantine_lock, flags);

  		cond_resched();

  		raw_spin_lock_irqsave(&quarantine_lock, flags);

  	}

  	raw_spin_unlock_irqrestore(&quarantine_lock, flags);

  
  	qlist_free_all(&to_free, cache);

  
  	synchronize_srcu(&remove_cache_srcu);

  }

  
  static int kasan_cpu_online(unsigned int cpu)
  {
  	this_cpu_ptr(&cpu_quarantine)->offline = false;
  	return 0;
  }
  
  static int kasan_cpu_offline(unsigned int cpu)
  {
  	struct qlist_head *q;
  
  	q = this_cpu_ptr(&cpu_quarantine);
  	/* Ensure the ordering between the writing to q->offline and
  	 * qlist_free_all. Otherwise, cpu_quarantine may be corrupted
  	 * by interrupt.
  	 */
  	WRITE_ONCE(q->offline, true);
  	barrier();
  	qlist_free_all(q, NULL);
  	return 0;
  }
  
  static int __init kasan_cpu_quarantine_init(void)
  {
  	int ret = 0;
  
  	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online",
  				kasan_cpu_online, kasan_cpu_offline);
  	if (ret < 0)
  		pr_err("kasan cpu quarantine register failed [%d]
  ", ret);
  	return ret;
  }
  late_initcall(kasan_cpu_quarantine_init);