Re: [PATCH 1/1] kasan: add memory corruption identification for hardware tag-based mode

From: Andrey Konovalov <andreyknvl@gmail.com>
To: Kuan-Ying Lee <kylee0686026@gmail.com>
Cc: Marco Elver <elver@google.com>,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Walter Wu <walter-zh.wu@mediatek.com>
Subject: Re: [PATCH 1/1] kasan: add memory corruption identification for hardware tag-based mode
Date: Wed, 2 Jun 2021 15:29:12 +0300	[thread overview]
Message-ID: <CA+fCnZeXEiTi-k4_XkYTvE2mQcXvP0Ct1N5VDEFfPufFqz15+Q@mail.gmail.com> (raw)
In-Reply-To: <20210531155912.GC622@DESKTOP-PJLD54P.localdomain>

On Mon, May 31, 2021 at 6:59 PM Kuan-Ying Lee <kylee0686026@gmail.com> wrote:
>
> > >
> > > +config KASAN_HW_TAGS_IDENTIFY
> > > +   bool "Enable memory corruption identification"
> > > +   depends on KASAN_HW_TAGS
> > > +   help
> > > +     This option enables best-effort identification of bug type
> > > +     (use-after-free or out-of-bounds) at the cost of increased
> > > +     memory consumption.
> >
> > Can we rename KASAN_SW_TAGS_IDENTIFY -> KASAN_TAGS_IDENTIFY in a
> > separate patch and then use that?
> >
> > Or do we have a problem renaming this options if there are existing
> > users of it?

Using the single KASAN_TAGS_IDENTIFY config option is what I would like to see.

Since this is a purely debugging feature for a less popular KASAN
mode, I think renaming the config name is OK.

> I tend to keep KASAN_SW_TAGS_IDENTIFY and KASAN_HW_TAGS_IDENTIFY
> separately.
>
> We need these two configs to decide how many stacks we will store.

You can define KASAN_NR_FREE_STACKS to different values depending on
whether HW_TAGS or SW_TAGS is in use. I don't see a problem here.

> If we store as many stacks as SW tag-based kasan does(5 stacks), we might
> mistake out-of-bound issues for use-after-free sometime. Becuase HW
> tag-based kasan only has 16 kinds of tags. When Out-of-bound issues happened, it might
> find the same tag in the stack we just stored and mistake happened.
> There is high probability that this mistake will happen.