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From:   Haibo Li <haibo.li@mediatek.com>
To:     <andreyknvl@gmail.com>
CC:     <akpm@linux-foundation.org>,
        <angelogioacchino.delregno@collabora.com>, <dvyukov@google.com>,
        <glider@google.com>, <haibo.li@mediatek.com>,
        <kasan-dev@googlegroups.com>,
        <linux-arm-kernel@lists.infradead.org>,
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        <lkp@intel.com>, <matthias.bgg@gmail.com>,
        <ryabinin.a.a@gmail.com>, <vincenzo.frascino@arm.com>,
        <xiaoming.yu@mediatek.com>
Subject: Re: [PATCH] fix comparison of unsigned expression < 0
Date:   Wed, 29 Nov 2023 11:42:47 +0800
Message-ID: <20231129034247.226365-1-haibo.li@mediatek.com>
In-Reply-To: <CA+fCnZcLwXn6crGF1E1cY3TknMaUN=H8-_hp0-cC+s8-wj95PQ@mail.gmail.com>
References: <CA+fCnZcLwXn6crGF1E1cY3TknMaUN=H8-_hp0-cC+s8-wj95PQ@mail.gmail.com>
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> On Wed, Nov 29, 2023 at 2:22 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Tue, 28 Nov 2023 15:55:32 +0800 Haibo Li <haibo.li@mediatek.com> wrote:
> >
> > > Kernel test robot reported:
> > >
> > > '''
> > > mm/kasan/report.c:637 kasan_non_canonical_hook() warn:
> > > unsigned 'addr' is never less than zero.
> > > '''
> > > The KASAN_SHADOW_OFFSET is 0 on loongarch64.
> > >
> > > To fix it,check the KASAN_SHADOW_OFFSET before do comparison.
> > >
> > > --- a/mm/kasan/report.c
> > > +++ b/mm/kasan/report.c
> > > @@ -634,10 +634,10 @@ void kasan_non_canonical_hook(unsigned long addr)
> > >  {
> > >       unsigned long orig_addr;
> > >       const char *bug_type;
> > > -
> > > +#if KASAN_SHADOW_OFFSET > 0
> > >       if (addr < KASAN_SHADOW_OFFSET)
> > >               return;
> > > -
> > > +#endif
> >
> > We'd rather not add ugly ifdefs for a simple test like this.  If we
> > replace "<" with "<=", does it fix?  I suspect that's wrong.
>
> Changing the comparison into "<=" would be wrong.
>
> But I actually don't think we need to fix anything here.
>
> This issue looks quite close to a similar comparison with 0 issue
> Linus shared his opinion on here:
>
> https://lore.kernel.org/all/Pine.LNX.4.58.0411230958260.20993@ppc970.osdl.org/
>
> I don't know if the common consensus with the regard to issues like
> that changed since then. But if not, perhaps we can treat this kernel
> test robot report as a false positive.
>
> Thanks!

Thanks for the information.Let's keep it as unchanged.