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

[Dev Jain <dev.jain@arm.com>]

On 13/06/26 5:46 am, Isaac Manjarres wrote:
> 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.

Thanks for testing Isaac! Do you have the bandwidth to carry out some
performance tests? We want to see whether this patchset gets perf boost
on some HW.

> 
> 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