[PATCH v3 mm 03/13] kasan: optimize large kmalloc poisoning

[Andrey Konovalov]

Similarly to kasan_kmalloc(), kasan_kmalloc_large() doesn't need
to unpoison the object as it as already unpoisoned by alloc_pages()
(or by ksize() for krealloc()).

This patch changes kasan_kmalloc_large() to only poison the redzone.

Reviewed-by: Marco Elver <el...@google.com>
Signed-off-by: Andrey Konovalov <andreyk...@google.com>
---
 mm/kasan/common.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 00edbc3eb32e..f2a6bae13053 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -494,7 +494,6 @@ EXPORT_SYMBOL(__kasan_kmalloc);
 void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
                                                gfp_t flags)
 {
-       struct page *page;
        unsigned long redzone_start;
        unsigned long redzone_end;
 
@@ -504,12 +503,23 @@ void * __must_check __kasan_kmalloc_large(const void 
*ptr, size_t size,
        if (unlikely(ptr == NULL))
                return NULL;
 
-       page = virt_to_page(ptr);
+       /*
+        * The object has already been unpoisoned by kasan_alloc_pages() for
+        * alloc_pages() or by ksize() for krealloc().
+        */
+
+       /*
+        * The redzone has byte-level precision for the generic mode.
+        * Partially poison the last object granule to cover the unaligned
+        * part of the redzone.
+        */
+       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+               kasan_poison_last_granule(ptr, size);
+
+       /* Poison the aligned part of the redzone. */
        redzone_start = round_up((unsigned long)(ptr + size),
                                KASAN_GRANULE_SIZE);
-       redzone_end = (unsigned long)ptr + page_size(page);
-
-       kasan_unpoison(ptr, size);
+       redzone_end = (unsigned long)ptr + page_size(virt_to_page(ptr));
        kasan_poison((void *)redzone_start, redzone_end - redzone_start,
                     KASAN_PAGE_REDZONE);
 
-- 
2.30.0.365.g02bc693789-goog