kasan: introduce kasan_mempool_unpoison_object

Introduce and document a kasan_mempool_unpoison_object hook.

This hook serves as a replacement for the generic kasan_unpoison_range
that the mempool code relies on right now.  mempool will be updated to use
the new hook in one of the following patches.

For now, define the new hook to be identical to kasan_unpoison_range.  One
of the following patches will update it to add stack trace collection.

Link: https://lkml.kernel.org/r/dae25f0e18ed8fd50efe509c5b71a0592de5c18d.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

@@ -228,6 +228,9 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip);
  * bugs and reports them. The caller can use the return value of this function
  * to find out if the allocation is buggy.
  *
+ * Before the poisoned allocation can be reused, it must be unpoisoned via
+ * kasan_mempool_unpoison_object().
+ *
  * This function operates on all slab allocations including large kmalloc
  * allocations (the ones returned by kmalloc_large() or by kmalloc() with the
  * size > KMALLOC_MAX_SIZE).
@@ -241,6 +244,32 @@ static __always_inline bool kasan_mempool_poison_object(void *ptr)
 	return true;
 }
 
+void __kasan_mempool_unpoison_object(void *ptr, size_t size, unsigned long ip);
+/**
+ * kasan_mempool_unpoison_object - Unpoison a mempool slab allocation.
+ * @ptr: Pointer to the slab allocation.
+ * @size: Size to be unpoisoned.
+ *
+ * This function is intended for kernel subsystems that cache slab allocations
+ * to reuse them instead of freeing them back to the slab allocator (e.g.
+ * mempool).
+ *
+ * This function unpoisons a slab allocation that was previously poisoned via
+ * kasan_mempool_poison_object() without initializing its memory. For the
+ * tag-based modes, this function does not assign a new tag to the allocation
+ * and instead restores the original tags based on the pointer value.
+ *
+ * This function operates on all slab allocations including large kmalloc
+ * allocations (the ones returned by kmalloc_large() or by kmalloc() with the
+ * size > KMALLOC_MAX_SIZE).
+ */
+static __always_inline void kasan_mempool_unpoison_object(void *ptr,
+							  size_t size)
+{
+	if (kasan_enabled())
+		__kasan_mempool_unpoison_object(ptr, size, _RET_IP_);
+}
+
 /*
  * Unlike kasan_check_read/write(), kasan_check_byte() is performed even for
  * the hardware tag-based mode that doesn't rely on compiler instrumentation.
@@ -301,6 +330,8 @@ static inline bool kasan_mempool_poison_object(void *ptr)
 {
 	return true;
 }
+static inline void kasan_mempool_unpoison_object(void *ptr, size_t size) {}
+
 static inline bool kasan_check_byte(const void *address)
 {
 	return true;

mm/kasan/common.c

@@ -451,6 +451,11 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
 	}
 }
 
+void __kasan_mempool_unpoison_object(void *ptr, size_t size, unsigned long ip)
+{
+	kasan_unpoison(ptr, size, false);
+}
+
 bool __kasan_check_byte(const void *address, unsigned long ip)
 {
 	if (!kasan_byte_accessible(address)) {