linux-kernel - Re: [PATCH v4 2/2] UML: add support for KASAN under x86

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Date:   Fri, 1 Jul 2022 11:16:53 +0200
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     David Gow <davidgow@...gle.com>
CC:     Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Johannes Berg <johannes@...solutions.net>,
        Patricia Alfonso <trishalfonso@...gle.com>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        "anton.ivanov@...bridgegreys.com" <anton.ivanov@...bridgegreys.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "linux-um@...ts.infradead.org" <linux-um@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Latypov <dlatypov@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "kunit-dev@...glegroups.com" <kunit-dev@...glegroups.com>
Subject: Re: [PATCH v4 2/2] UML: add support for KASAN under x86_64

On Fri, Jul 01, 2022 at 11:08:27AM +0200, David Gow wrote:
> On Thu, Jun 30, 2022 at 9:29 PM Andrey Konovalov <andreyknvl@...il.com> wrote:
> > Stack trace collection code might trigger KASAN splats when walking
> > stack frames, but this can be resolved by using unchecked accesses.
> > The main reason to disable instrumentation here is for performance
> > reasons, see the upcoming patch for arm64 [1] for some details.
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=802b91118d11
> 
> Ah -- that does it! Using READ_ONCE_NOCHECK() in dump_trace() gets rid
> of the nasty recursive KASAN failures we were getting in the tests.
> 
> I'll send out v5 with those files instrumented again.

Hmm, do we really want that?  In the patch Andrey linked to above he
removed the READ_ONCE_NOCHECK() and added the KASAN_SANITIZE on the
corresponding files for arm64, just like it's already the case in this
patch for UML.