From: Juntong Deng <juntong.deng@outlook.com>
To: ryabinin.a.a@gmail.com, glider@google.com, andreyknvl@gmail.com,
dvyukov@google.com, vincenzo.frascino@arm.com,
akpm@linux-foundation.org
Cc: kasan-dev@googlegroups.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
linux-kernel-mentees@lists.linuxfoundation.org
Subject: [PATCH v3] kasan: Improve free meta storage in Generic KASAN
Date: Wed, 22 Nov 2023 18:46:31 +0000 [thread overview]
Message-ID: <VI1P193MB0752675D6E0A2D16CE656F8299BAA@VI1P193MB0752.EURP193.PROD.OUTLOOK.COM> (raw)
Currently free meta can only be stored in object if the object is
not smaller than free meta.
After the improvement, when the object is smaller than free meta and
SLUB DEBUG is not enabled, it is possible to store part of the free
meta in the object, reducing the increased size of the red zone.
Example:
free meta size: 16 bytes
alloc meta size: 16 bytes
object size: 8 bytes
optimal redzone size (object_size <= 64): 16 bytes
Before improvement:
actual redzone size = alloc meta size + free meta size = 32 bytes
After improvement:
actual redzone size = alloc meta size + (free meta size - object size)
= 24 bytes
Suggested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Juntong Deng <juntong.deng@outlook.com>
---
V2 -> V3: When SLUB DEBUG is enabled, the previous free meta
storage method continues to be used. Cancel the change to
kasan_metadata_size().
V1 -> V2: Make kasan_metadata_size() adapt to the improved
free meta storage
mm/kasan/generic.c | 39 +++++++++++++++++++++++++++++----------
1 file changed, 29 insertions(+), 10 deletions(-)
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 4d837ab83f08..97713251053c 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -361,6 +361,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
{
unsigned int ok_size;
unsigned int optimal_size;
+ unsigned int rem_free_meta_size;
+ unsigned int orig_alloc_meta_offset;
if (!kasan_requires_meta())
return;
@@ -394,6 +396,9 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
/* Continue, since free meta might still fit. */
}
+ ok_size = *size;
+ orig_alloc_meta_offset = cache->kasan_info.alloc_meta_offset;
+
/*
* Add free meta into redzone when it's not possible to store
* it in the object. This is the case when:
@@ -401,23 +406,37 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
* be touched after it was freed, or
* 2. Object has a constructor, which means it's expected to
* retain its content until the next allocation, or
- * 3. Object is too small.
+ * 3. Object is too small and SLUB DEBUG is enabled. Avoid
+ * free meta that exceeds the object size corrupts the
+ * SLUB DEBUG metadata.
* Otherwise cache->kasan_info.free_meta_offset = 0 is implied.
+ * If the object is smaller than the free meta and SLUB DEBUG
+ * is not enabled, it is still possible to store part of the
+ * free meta in the object.
*/
- if ((cache->flags & SLAB_TYPESAFE_BY_RCU) || cache->ctor ||
- cache->object_size < sizeof(struct kasan_free_meta)) {
- ok_size = *size;
-
+ if ((cache->flags & SLAB_TYPESAFE_BY_RCU) || cache->ctor) {
cache->kasan_info.free_meta_offset = *size;
*size += sizeof(struct kasan_free_meta);
-
- /* If free meta doesn't fit, don't add it. */
- if (*size > KMALLOC_MAX_SIZE) {
- cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META;
- *size = ok_size;
+ } else if (cache->object_size < sizeof(struct kasan_free_meta)) {
+ if (__slub_debug_enabled()) {
+ cache->kasan_info.free_meta_offset = *size;
+ *size += sizeof(struct kasan_free_meta);
+ } else {
+ rem_free_meta_size = sizeof(struct kasan_free_meta) -
+ cache->object_size;
+ *size += rem_free_meta_size;
+ if (cache->kasan_info.alloc_meta_offset != 0)
+ cache->kasan_info.alloc_meta_offset += rem_free_meta_size;
}
}
+ /* If free meta doesn't fit, don't add it. */
+ if (*size > KMALLOC_MAX_SIZE) {
+ cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META;
+ cache->kasan_info.alloc_meta_offset = orig_alloc_meta_offset;
+ *size = ok_size;
+ }
+
/* Calculate size with optimal redzone. */
optimal_size = cache->object_size + optimal_redzone(cache->object_size);
/* Limit it with KMALLOC_MAX_SIZE (relevant for SLAB only). */
--
2.39.2
next reply other threads:[~2023-11-22 18:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-22 18:46 Juntong Deng [this message]
2023-11-23 10:43 ` [PATCH v3] kasan: Improve free meta storage in Generic KASAN Juntong Deng
2023-11-23 16:04 ` Andrey Konovalov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=VI1P193MB0752675D6E0A2D16CE656F8299BAA@VI1P193MB0752.EURP193.PROD.OUTLOOK.COM \
--to=juntong.deng@outlook.com \
--cc=akpm@linux-foundation.org \
--cc=andreyknvl@gmail.com \
--cc=dvyukov@google.com \
--cc=glider@google.com \
--cc=kasan-dev@googlegroups.com \
--cc=linux-kernel-mentees@lists.linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=ryabinin.a.a@gmail.com \
--cc=vincenzo.frascino@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).