linux-kernel - Re: [PATCH] fix comparison of unsigned expression

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Date:   Wed, 29 Nov 2023 11:42:47 +0800
From:   Haibo Li <haibo.li@...iatek.com>
To:     <andreyknvl@...il.com>
CC:     <akpm@...ux-foundation.org>,
        <angelogioacchino.delregno@...labora.com>, <dvyukov@...gle.com>,
        <glider@...gle.com>, <haibo.li@...iatek.com>,
        <kasan-dev@...glegroups.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <linux-mm@...ck.org>,
        <lkp@...el.com>, <matthias.bgg@...il.com>,
        <ryabinin.a.a@...il.com>, <vincenzo.frascino@....com>,
        <xiaoming.yu@...iatek.com>
Subject: Re: [PATCH] fix comparison of unsigned expression < 0

> On Wed, Nov 29, 2023 at 2:22 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > On Tue, 28 Nov 2023 15:55:32 +0800 Haibo Li <haibo.li@...iatek.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.