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Subject[PATCH v2 03/12] kasan: optimize large kmalloc poisoning
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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 <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@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
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