kasan: introduce kasan_mempool_poison_pages

Introduce and document a kasan_mempool_poison_pages hook to be used by the
mempool code instead of kasan_poison_pages.

Compated to kasan_poison_pages, the new hook:

1. For the tag-based modes, skips checking and poisoning allocations that
   were not tagged due to sampling.

2. Checks for double-free and invalid-free bugs.

In the future, kasan_poison_pages can also be updated to handle #2, but
this is out-of-scope of this series.

Link: https://lkml.kernel.org/r/88dc7340cce28249abf789f6e0c792c317df9ba5.1703024586.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/kasan.h

@@ -212,6 +212,29 @@ static __always_inline void * __must_check kasan_krealloc(const void *object,
 	return (void *)object;
 }
 
+bool __kasan_mempool_poison_pages(struct page *page, unsigned int order,
+				  unsigned long ip);
+/**
+ * kasan_mempool_poison_pages - Check and poison a mempool page allocation.
+ * @page: Pointer to the page allocation.
+ * @order: Order of the allocation.
+ *
+ * This function is intended for kernel subsystems that cache page allocations
+ * to reuse them instead of freeing them back to page_alloc (e.g. mempool).
+ *
+ * This function is similar to kasan_mempool_poison_object() but operates on
+ * page allocations.
+ *
+ * Return: true if the allocation can be safely reused; false otherwise.
+ */
+static __always_inline bool kasan_mempool_poison_pages(struct page *page,
+						       unsigned int order)
+{
+	if (kasan_enabled())
+		return __kasan_mempool_poison_pages(page, order, _RET_IP_);
+	return true;
+}
+
 bool __kasan_mempool_poison_object(void *ptr, unsigned long ip);
 /**
  * kasan_mempool_poison_object - Check and poison a mempool slab allocation.
@@ -326,6 +349,10 @@ static inline void *kasan_krealloc(const void *object, size_t new_size,
 {
 	return (void *)object;
 }
+static inline bool kasan_mempool_poison_pages(struct page *page, unsigned int order)
+{
+	return true;
+}
 static inline bool kasan_mempool_poison_object(void *ptr)
 {
 	return true;

mm/kasan/common.c

@@ -426,6 +426,29 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
 		return ____kasan_kmalloc(slab->slab_cache, object, size, flags);
 }
 
+bool __kasan_mempool_poison_pages(struct page *page, unsigned int order,
+				  unsigned long ip)
+{
+	unsigned long *ptr;
+
+	if (unlikely(PageHighMem(page)))
+		return true;
+
+	/* Bail out if allocation was excluded due to sampling. */
+	if (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+	    page_kasan_tag(page) == KASAN_TAG_KERNEL)
+		return true;
+
+	ptr = page_address(page);
+
+	if (check_page_allocation(ptr, ip))
+		return false;
+
+	kasan_poison(ptr, PAGE_SIZE << order, KASAN_PAGE_FREE, false);
+
+	return true;
+}
+
 bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
 {
 	struct folio *folio;