Re: [PATCH 2/2] kasan, mm: reset tag for hex dump address

[Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>]

On Tue, 2021-07-27 at 09:20 +0200, Marco Elver wrote:
> On Tue, 27 Jul 2021 at 06:00, Kuan-Ying Lee <
> Kuan-Ying.Lee@mediatek.com> wrote:
> > 
> > Text is a string. We need to move this kasan_reset_tag()
> > to address but text.
> > 
> > Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
> 
> This patch also makes sense (I think), thanks for sending. But it's
> unclear what the problem is. The fact that when the address is
> printed
> it still includes the tag? Or a false positive?
> It'd be good to clarify in the commit message.

Yes, printed address includes the tag, so when we access the
metadata, we will encounter tag mismatch with HW tag-based kasan
enabled.

> 
> Here I'd also use a more descriptive patch title, something like
> "kasan, slub: reset tag when printing address".
> 
> Also, I think this patch requires a:
> 
>   Fixes: aa1ef4d7b3f6 ("kasan, mm: reset tags when accessing
> metadata")
> 
> So that stable kernels can pick this up if appropriate.

Thank you, Marco.
I will refine commit message in the v2.

> 
> > ---
> >  mm/slub.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 6dad2b6fda6f..d20674f839ba 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -576,8 +576,8 @@ static void print_section(char *level, char
> > *text, u8 *addr,
> >                           unsigned int length)
> >  {
> >         metadata_access_enable();
> > -       print_hex_dump(level, kasan_reset_tag(text),
> > DUMP_PREFIX_ADDRESS,
> > -                       16, 1, addr, length, 1);
> > +       print_hex_dump(level, text, DUMP_PREFIX_ADDRESS,
> > +                       16, 1, kasan_reset_tag((void *)addr),
> > length, 1);
> >         metadata_access_disable();
> >  }
> > 
> > --
> > 2.18.0
> > 
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