#include <linux/kernel.h>

  #include <linux/string.h>

  #include <linux/mm.h>

  #include <linux/highmem.h>

  #include <linux/page_ext.h>

  #include <linux/poison.h>

  #include <linux/ratelimit.h>

  static bool __page_poisoning_enabled __read_mostly;
  static bool want_page_poisoning __read_mostly;

  static int early_page_poison_param(char *buf)

  {

  	if (!buf)
  		return -EINVAL;

  	return strtobool(buf, &want_page_poisoning);

  }
  early_param("page_poison", early_page_poison_param);
  
  bool page_poisoning_enabled(void)
  {
  	return __page_poisoning_enabled;
  }
  
  static bool need_page_poisoning(void)
  {
  	return want_page_poisoning;

  }
  
  static void init_page_poisoning(void)
  {

  	/*
  	 * page poisoning is debug page alloc for some arches. If either
  	 * of those options are enabled, enable poisoning
  	 */
  	if (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC)) {
  		if (!want_page_poisoning && !debug_pagealloc_enabled())
  			return;
  	} else {
  		if (!want_page_poisoning)
  			return;
  	}

  	__page_poisoning_enabled = true;

  }
  
  struct page_ext_operations page_poisoning_ops = {
  	.need = need_page_poisoning,
  	.init = init_page_poisoning,
  };

  static inline void set_page_poison(struct page *page)
  {

  	struct page_ext *page_ext;
  
  	page_ext = lookup_page_ext(page);

  	if (unlikely(!page_ext))
  		return;

  	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);

  }
  
  static inline void clear_page_poison(struct page *page)
  {

  	struct page_ext *page_ext;
  
  	page_ext = lookup_page_ext(page);

  	if (unlikely(!page_ext))
  		return;

  	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);

  }

  bool page_is_poisoned(struct page *page)

  {

  	struct page_ext *page_ext;
  
  	page_ext = lookup_page_ext(page);

  	if (unlikely(!page_ext))

  		return false;

  	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);

  }

  static void poison_page(struct page *page)
  {

  	void *addr = kmap_atomic(page);

  	set_page_poison(page);

  	memset(addr, PAGE_POISON, PAGE_SIZE);

  	kunmap_atomic(addr);

  }
  
  static void poison_pages(struct page *page, int n)
  {
  	int i;
  
  	for (i = 0; i < n; i++)
  		poison_page(page + i);
  }
  
  static bool single_bit_flip(unsigned char a, unsigned char b)
  {
  	unsigned char error = a ^ b;
  
  	return error && !(error & (error - 1));
  }
  
  static void check_poison_mem(unsigned char *mem, size_t bytes)
  {

  	static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);

  	unsigned char *start;
  	unsigned char *end;

  	if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
  		return;

  	start = memchr_inv(mem, PAGE_POISON, bytes);
  	if (!start)

  		return;
  
  	for (end = mem + bytes - 1; end > start; end--) {
  		if (*end != PAGE_POISON)
  			break;
  	}

  	if (!__ratelimit(&ratelimit))

  		return;
  	else if (start == end && single_bit_flip(*start, PAGE_POISON))

  		pr_err("pagealloc: single bit error
  ");

  	else

  		pr_err("pagealloc: memory corruption
  ");

  
  	print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
  			end - start + 1, 1);
  	dump_stack();
  }

  static void unpoison_page(struct page *page)
  {

  	void *addr;

  	if (!page_is_poisoned(page))

  		return;

  	addr = kmap_atomic(page);
  	check_poison_mem(addr, PAGE_SIZE);
  	clear_page_poison(page);
  	kunmap_atomic(addr);

  }
  
  static void unpoison_pages(struct page *page, int n)
  {
  	int i;
  
  	for (i = 0; i < n; i++)
  		unpoison_page(page + i);
  }

  void kernel_poison_pages(struct page *page, int numpages, int enable)

  {

  	if (!page_poisoning_enabled())

  		return;

  	if (enable)
  		unpoison_pages(page, numpages);
  	else
  		poison_pages(page, numpages);
  }

  
  #ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
  void __kernel_map_pages(struct page *page, int numpages, int enable)
  {
  	/* This function does nothing, all work is done via poison pages */
  }
  #endif