Date:   Wed,  7 Sep 2022 15:10:19 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jonathan Corbet <corbet@....net>
Cc:     Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        Feng Tang <feng.tang@...el.com>
Subject: [PATCH v5 0/4] mm/slub: some debug enhancements for kmalloc 

kmalloc's API family is critical for mm, and one of its nature is that
it will round up the request size to a fixed one (mostly power of 2).
When user requests memory for '2^n + 1' bytes, actually 2^(n+1) bytes
could be allocated, so in worst case, there is around 50% memory space
waste.

The wastage is not a big issue for requests that get allocated/freed 
quickly, but may cause problems with objects that have longer life time,
and there were some OOM cases in some extrem cases.

This patchset tries to :
* Add a debug method to track each kmalloced object's wastage info,
  and show the call stack of original allocation (depends on
  SLAB_STORE_USER flag)
* Extend the redzone sanity check to the extra kmalloced buffer than
  requested, to better detect un-legitimate access to it. (depends
  on SLAB_STORE_USER & SLAB_RED_ZONE)

The redzone part has been tested with code below:

	for (shift = 3; shift <= 12; shift++) {
		size = 1 << shift;
		buf = kmalloc(size + 4, GFP_KERNEL);
		/* We have 96, 196 kmalloc size, which is not power of 2 */
		if (size == 64 || size == 128)
			oob_size = 16;
		else
			oob_size = size - 4;
		memset(buf + size + 4, 0xee, oob_size);
		kfree(buf);
	}

Please help to review, thanks!

- Feng

---
Changelogs:
 
  since v4:
    * fix a race issue in v3, by moving kmalloc debug init into
      alloc_debug_processing (Hyeonggon Yoo)
    * add 'partial_conext' for better parameter passing in get_partial()
      call chain (Vlastimil Babka)
    * update 'slub.rst' for 'alloc_traces' part (Hyeonggon Yoo)
    * update code comments for 'orig_size'

  since v3:
    * rebase against latest post 6.0-rc1 slab tree's 'for-next' branch  
    * fix a bug reported by 0Day, that kmalloc-redzoned data and kasan's
      free meta data overlaps in the same kmalloc object data area 

  since v2:
    * rebase against slab tree's 'for-next' branch
    * fix pointer handling (Kefeng Wang)
    * move kzalloc zeroing handling change to a separate patch (Vlastimil Babka) 
    * make 'orig_size' only depend on KMALLOC & STORE_USER flag
      bits (Vlastimil Babka)

  since v1:
    * limit the 'orig_size' to kmalloc objects only, and save
      it after track in metadata (Vlastimil Babka)
    * fix a offset calculation problem in print_trailer

  since RFC:
    * fix problems in kmem_cache_alloc_bulk() and records sorting,
      improve the print format (Hyeonggon Yoo)
    * fix a compiling issue found by 0Day bot
    * update the commit log based info from iova developers

Feng Tang (4):
  mm/slub: enable debugging memory wasting of kmalloc
  mm/slub: only zero the requested size of buffer for kzalloc
  mm: kasan: Add free_meta size info in struct kasan_cache
  mm/slub: extend redzone check to extra allocated kmalloc space than
    requested

 Documentation/mm/slub.rst |  33 +++---
 include/linux/kasan.h     |   2 +
 include/linux/slab.h      |   2 +
 mm/kasan/common.c         |   2 +
 mm/slab.c                 |   6 +-
 mm/slab.h                 |  13 ++-
 mm/slab_common.c          |   4 +
 mm/slub.c                 | 219 ++++++++++++++++++++++++++++++--------
 8 files changed, 220 insertions(+), 61 deletions(-)

-- 
2.34.1

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