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 11:36 am, Lance Yang 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.
> 
> Hmm ... do we also need to teach the KASAN KUnit tests about this mode?
> 
> With kasan.tag_only_on_alloc=on, free-time poisoning is skipped, so
> some UAF and double-free reports are skipped on purpose, but the tests
> still expect them :)

Yeah my opinion is that we shouldn't bother - but if we go ahead with this
patch in some shape or form then I'll see how to make kasan_test work with
this.

> 
> Cheers, Lance
>