Re: [PATCH v2 0/5] mm/slub: Improve data handling of krealloc() when orig_size is enabled
From: Vlastimil Babka
Date: Wed Oct 02 2024 - 06:42:48 EST
On 9/11/24 08:45, Feng Tang wrote:
> Danilo Krummrich's patch [1] raised one problem about krealloc() that
> its caller doesn't pass the old request size, say the object is 64
> bytes kmalloc one, but caller originally only requested 48 bytes. Then
> when krealloc() shrinks or grows in the same object, or allocate a new
> bigger object, it lacks this 'original size' information to do accurate
> data preserving or zeroing (when __GFP_ZERO is set).
>
> Thus with slub debug redzone and object tracking enabled, parts of the
> object after krealloc() might contain redzone data instead of zeroes,
> which is violating the __GFP_ZERO guarantees. Good thing is in this
> case, kmalloc caches do have this 'orig_size' feature, which could be
> used to improve the situation here.
>
> To make the 'orig_size' accurate, we adjust some kasan/slub meta data
> handling. Also add a slub kunit test case for krealloc().
>
> This patchset has dependency over patches in both -mm tree and -slab
> trees, so it is written based on linux-next tree '20240910' version.
>
> [1]. https://lore.kernel.org/lkml/20240812223707.32049-1-dakr@xxxxxxxxxx/
Thanks, added to slab/for-next
>
> Thanks,
> Feng
>
> Changelog:
>
> Since v1:
> * Drop the patch changing generic kunit code from this patchset,
> and will send it separately.
> * Separate the krealloc moving form slab_common.c to slub.c to a
> new patch for better review (Danilo/Vlastimil)
> * Improve commit log and comments (Vlastimil/Danilo)
> * Rework the kunit test case to remove its dependency over
> slub_debug (which is incomplete in v1) (Vlastimil)
> * Add ack and review tag from developers.
>
> Feng Tang (5):
> mm/kasan: Don't store metadata inside kmalloc object when
> slub_debug_orig_size is on
> mm/slub: Consider kfence case for get_orig_size()
> mm/slub: Move krealloc() and related code to slub.c
> mm/slub: Improve redzone check and zeroing for krealloc()
> mm/slub, kunit: Add testcase for krealloc redzone and zeroing
>
> lib/slub_kunit.c | 42 +++++++++++++++
> mm/kasan/generic.c | 7 ++-
> mm/slab.h | 6 +++
> mm/slab_common.c | 84 ------------------------------
> mm/slub.c | 125 ++++++++++++++++++++++++++++++++++++++-------
> 5 files changed, 160 insertions(+), 104 deletions(-)
>