linux-kernel - Re: [PATCH mm] arm64: kasan: fix MTE symbols exports

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Date:   Thu, 11 Feb 2021 18:30:10 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Christoph Hellwig <hch@...radead.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH mm] arm64: kasan: fix MTE symbols exports

On Tue, Feb 9, 2021 at 7:45 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Tue, 9 Feb 2021 17:02:56 +0000 Catalin Marinas <catalin.marinas@....com> wrote:
>
> > On Tue, Feb 09, 2021 at 04:32:30PM +0100, Andrey Konovalov wrote:
> > > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> > > index a66c2806fc4d..788ef0c3a25e 100644
> > > --- a/arch/arm64/kernel/mte.c
> > > +++ b/arch/arm64/kernel/mte.c
> > > @@ -113,13 +113,17 @@ void mte_enable_kernel(void)
> > >     sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
> > >     isb();
> > >  }
> > > +#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
> > >  EXPORT_SYMBOL_GPL(mte_enable_kernel);
> > > +#endif
> > >
> > >  void mte_set_report_once(bool state)
> > >  {
> > >     WRITE_ONCE(report_fault_once, state);
> > >  }
> > > +#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
> > >  EXPORT_SYMBOL_GPL(mte_set_report_once);
> > > +#endif
> >
> > Do we actually care about exporting them when KASAN_KUNIT_TEST=n? It
> > looks weird to have these #ifdefs in the arch code. Either the
> > arch-kasan API requires these symbols to be exported to modules or not.
> > I'm not keen on such kasan internals trickling down into the arch code.

Understood.

> > If you don't want to export them in the KASAN_KUNIT_TEST=n case, add a
> > wrapper in the kasan built-in code (e.g. kasan_test_enable_tagging,
> > kasan_test_set_report_once) and conditionally compile them based on
> > KASAN_KUNIT_TEST.

This might be a better approach indeed.

> In other words, the patch's changelog was poor!  It told us what the
> patch does (which is often obvious from the code) but it failed to
> explain why the patch does what it does.
>
> The same goes for code comments, folks - please explain "why it does
> this" rather than "what it does".

I'm sorry, Andrew.

Could you please drop the "arm64: kasan: export MTE symbols for KASAN
tests" patch from the mm tree (but keep the rest of that series)?

I'll post a separate patch with a fix.

Thanks!