[v4,0/4] mm/slub: some debug enhancements for kmalloc objects

Message

Feng Tang Aug. 29, 2022, 7:56 a.m. UTC

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 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 cover extra allocated kmalloc space
    than requested

 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             | 168 +++++++++++++++++++++++++++++++++++++-----
 7 files changed, 172 insertions(+), 25 deletions(-)