Re: [PATCH 2/8] kasan: test: avoid writing invalid memory

From: Andrey Konovalov <andreyknvl@gmail.com>
To: Marco Elver <elver@google.com>
Cc: andrey.konovalov@linux.dev,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Alexander Potapenko <glider@google.com>,
	kasan-dev <kasan-dev@googlegroups.com>,
	Linux Memory Management List <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/8] kasan: test: avoid writing invalid memory
Date: Thu, 12 Aug 2021 15:02:20 +0200	[thread overview]
Message-ID: <CA+fCnZfGagaxUkrr5FxaQwTVr+C5OpmahPgiwCuXeZkp2nNOkg@mail.gmail.com> (raw)
In-Reply-To: <CANpmjNM6hn8UrozaptUacuNJ7EtsprDJWDmOk-F6BaNZ6Hgchg@mail.gmail.com>

On Thu, Aug 12, 2021 at 10:57 AM Marco Elver <elver@google.com> wrote:
>
> On Wed, 11 Aug 2021 at 21:21, <andrey.konovalov@linux.dev> wrote:
> > From: Andrey Konovalov <andreyknvl@gmail.com>
> >
> > Multiple KASAN tests do writes past the allocated objects or writes to
> > freed memory. Turn these writes into reads to avoid corrupting memory.
> > Otherwise, these tests might lead to crashes with the HW_TAGS mode, as it
> > neither uses quarantine nor redzones.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>
>
> Reviewed-by: Marco Elver <elver@google.com>
>
> although if you need a write primitive somewhere that doesn't corrupt
> memory, you could use atomic_add() or atomic_or() of 0. Although
> technically that's a read-modify-write.

Interesting idea. I'd say let's keep the volatile reads for now, and
change them if we encounter any problem with those.

> For generic mode one issue is
> that these are explicitly instrumented and not through the compiler,
> which is only a problem if you're testing the compiler emits the right
> instrumentation.

On a related point, it seems we have no KASAN tests to check atomic operations.

Filed https://bugzilla.kernel.org/show_bug.cgi?id=214055 for this.

Thanks!