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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Sat, 16 Jul 2022 20:43:06 +0200
Message-ID: <CAMuHMdWSsibmL=LauLm+OTn0SByLA4tGsbhbMsnvSRdb381RTQ@mail.gmail.com>
Subject: Re: [PATCH v2 1/1] mm: kfence: apply kmemleak_ignore_phys on early
 allocated pool
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     yee.lee@mediatek.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "open list:KFENCE" <kasan-dev@googlegroups.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@lists.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>
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Hi Andrew,

On Sat, Jul 16, 2022 at 1:33 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> On Fri, 15 Jul 2022 10:17:43 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Tue, Jun 28, 2022 at 1:42 PM <yee.lee@mediatek.com> wrote:
> > > From: Yee Lee <yee.lee@mediatek.com>
> > >
> > > This patch solves two issues.
> > >
> > > (1) The pool allocated by memblock needs to unregister from
> > > kmemleak scanning. Apply kmemleak_ignore_phys to replace the
> > > original kmemleak_free as its address now is stored in the phys tree.
> > >
> > > (2) The pool late allocated by page-alloc doesn't need to unregister.
> > > Move out the freeing operation from its call path.
> > >
> > > Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> > > Suggested-by: Marco Elver <elver@google.com>
> > > Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> >
> > Thank you, this fixes the storm of
> >
> >     BUG: KFENCE: invalid read in scan_block+0x78/0x130
> >     BUG: KFENCE: use-after-free read in scan_block+0x78/0x130
> >     BUG: KFENCE: out-of-bounds read in scan_block+0x78/0x130
> >
> > messages I was seeing on arm64.
>
> Thanks, but...
>
> - It would be great if we could identify a Fixes: for this.

IIRC, I started seeing the issue with "[PATCH v4 3/4] mm:
kmemleak: add rbtree and store physical address for objects
allocated with PA" (i.e. commit 0c24e061196c21d5 ("mm: kmemleak:
add rbtree and store physical address for objects allocated
with PA")) of series "[PATCH v4 0/4] mm: kmemleak: store objects
allocated with physical address separately and check when scan"
(https://lore.kernel.org/all/20220611035551.1823303-1-patrick.wang.shcn@gmail.com),
in an arm64 config that had enabled kfence.
So I think this patch is sort of a dependency for that series.

I had cherry-picked that series after bisecting a regression to
commit 23c2d497de21f258 ("mm: kmemleak: take a full lowmem check in
kmemleak_*_phys()") in v5.18-rc3, and having a look around.

> - This patch has been accused of crashing the kernel:
>
>         https://lkml.kernel.org/r/YsFeUHkrFTQ7T51Q@xsang-OptiPlex-9020
>
>   Do we think that report is bogus?

I think all of this is highly architecture-specific...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds