Re: [RFC PATCH 0/2] kasan: hw_tags: Add option to tag only at allocation time

[Isaac Manjarres <isaacmanjarres@google.com>]

On Fri, Jun 12, 2026 at 04:44:22AM +0000, Dev Jain wrote:
> Introduce a boot option to tag only at allocation time of the objects. This
> reduces KASAN MTE overhead, the tradeoff being reduced ability of
> catching bugs.
> 
> Now, when a memory object will be freed, it will retain the random tag it
> had at allocation time. This compromises on catching UAF bugs, till the
> time the object is not reallocated, at which point it will have a new
> random tag.
> 
> Hence, not catching "use-after-free-before-reallocation" and not catching
> "double-free" will be the compromise for reduced KASAN overhead.
> 
> This is an RFC because we are not clear about the performance benefit.
> 
> Android folks, please help with testing!
> 
> ---
> Applies on Linus master (9716c086c8e8).
> 
> Dev Jain (2):
>   kasan: hw_tags: Use KASAN_PAGE_REDZONE for vmalloc redzoning
>   kasan: hw_tags: Add boot option to elide free time poisoning
> 
>  Documentation/dev-tools/kasan.rst |  4 +++
>  mm/kasan/hw_tags.c                | 45 +++++++++++++++++++++++++++++--
>  mm/kasan/kasan.h                  | 23 +++++++++++++++-
>  3 files changed, 69 insertions(+), 3 deletions(-)
> 
> -- 
> 2.43.0

I tested out this series on one of our devices that has MTE support,
and didn't see any functional issues.

One thing I did notice though, and it's independent of this patch, is
that the vmalloc_oob is failing, but that happens even if these patches
aren't present.

Thanks,
Isaac