Re: [PATCH v3 0/2] Refine kmalloc caches randomization in kvmalloc

[Harry Yoo]

On Wed, Feb 12, 2025 at 04:15:03PM +0800, GONG Ruiqi wrote:
> Hi,
> 
> v3:
>   - move all the way from kmalloc_gfp_adjust to kvrealloc_noprof into
>     mm/slub.c
>   - some rewording for commit logs
> v2: https://lore.kernel.org/all/20250208014723.1514049-1-gongruiqi1@xxxxxxxxxx/
>   - change the implementation as Vlastimil suggested
> v1: https://lore.kernel.org/all/20250122074817.991060-1-gongruiqi1@xxxxxxxxxx/
> 
> Tamás reported [1] that kmalloc cache randomization doesn't actually
> work for those kmalloc invoked via kvmalloc. For more details, see the
> commit log of patch 2.
> 
> The current solution requires a direct call from __kvmalloc_node_noprof
> to __do_kmalloc_node, a static function in a different .c file. As
> suggested by Vlastimil [2], it's achieved by simply moving
> __kvmalloc_node_noprof from mm/util.c to mm/slub.c, together with some
> other functions of the same family.

Hi, GONG!
Sorry for my late review.

This patch series looks good to me (with a nit),
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>

Also, I verified that the problem you described exists on slab/for-next,
and the patch series fixes the problem. Please feel free to add,
Tested-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>

nit: Does it make sense to call __kvmalloc_node_track_caller_noprof()
instead of __do_kmalloc_node() to avoid bloating the code size?

My simple build test says it saves 1592 bytes:
  $ ./scripts/bloat-o-meter slub.o.before slub.o.after
  add/remove: 0/1 grow/shrink: 0/1 up/down: 0/-1592 (-1592)
  Function                                     old     new   delta
  __kvmalloc_node_noprof.cold                   39       -     -39
  __kvmalloc_node_noprof                      1755     202   -1553
  Total: Before=79723, After=78131, chg -2.00%

> Link: https://github.com/google/security-research/blob/908d59b573960dc0b90adda6f16f7017aca08609/pocs/linux/kernelctf/CVE-2024-27397_mitigation/docs/exploit.md?plain=1#L259 [1]
> Link: https://lore.kernel.org/all/62044279-0c56-4185-97f7-7afac65ff449@xxxxxxx/ [2]

-- 
Harry