linux-kernel - Re: [PATCH] kfence: unpoison pool region before use

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Message-ID: <CANpmjNP+p6QyOJnMmtrG-d4bSrhRZoGVGfvp=-WNHL8kpXHUUg@mail.gmail.com>
Date:   Sat, 3 Apr 2021 16:45:13 +0200
From:   Marco Elver <elver@...gle.com>
To:     Andrey Konovalov <andreyknvl@...il.com>
Cc:     Peter Collingbourne <pcc@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kfence: unpoison pool region before use

On Sat, 3 Apr 2021 at 16:05, Andrey Konovalov <andreyknvl@...il.com> wrote:
...
> Which kasan_byte_accessible() call fails?
>
> KASAN checks shouldn't be performed for KFENCE objects. We have a
> number of is_kfence_address() checks in KASAN runtime, but maybe we're
> missing some. Perhaps, we should even move those checks into the
> high-level wrappers in include/linux/kasan.h.

Moving them into include/linux/kasan.h seems unnecessary and an easy
way to introduce unnecessary overhead. AFAIK, there should be no
difference between having them in the high-level wrappers and the
inner runtime functions. I think until we understand what is actually
going on and could thoroughly justify, I'd be opposed to larger
changes. The small patch here is innocent enough, but it'd still be
good to understand. (FWIW, I believe the issue was encountered with
SW_TAGS on a downstream kernel.)