linux-kernel - Re: [PATCH] xen: unexport __init-annotated xen_xlate_map_ballooned

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Date:   Mon, 6 Jun 2022 16:43:35 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Oleksandr <olekstysh@...il.com>
cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        moderated for non-subscribers <xen-devel@...ts.xenproject.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Julien Grall <julien.grall@....com>,
        Shannon Zhao <shannon.zhao@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen: unexport __init-annotated
 xen_xlate_map_ballooned_pages()

On Mon, 6 Jun 2022, Oleksandr wrote:
> On 06.06.22 07:59, Masahiro Yamada wrote:
> 
> Hello
> 
> > EXPORT_SYMBOL and __init is a bad combination because the .init.text
> > section is freed up after the initialization. Hence, modules cannot
> > use symbols annotated __init. The access to a freed symbol may end up
> > with kernel panic.
> > 
> > modpost used to detect it, but it has been broken for a decade.
> > 
> > Recently, I fixed modpost so it started to warn it again, then this
> > showed up in linux-next builds.
> > 
> > There are two ways to fix it:
> > 
> >    - Remove __init
> >    - Remove EXPORT_SYMBOL
> > 
> > I chose the latter for this case because none of the in-tree call-sites
> > (arch/arm/xen/enlighten.c, arch/x86/xen/grant-table.c) is compiled as
> > modular.
> 
> Good description.
> 
> 
> > 
> > Fixes: 243848fc018c ("xen/grant-table: Move xlated_setup_gnttab_pages to
> > common place")
> > Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> 
> I think the patch is correct.
> 
> Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>

Acked-by: Stefano Stabellini <sstabellini@...nel.org>


> > ---
> > 
> >   drivers/xen/xlate_mmu.c | 1 -
> >   1 file changed, 1 deletion(-)
> > 
> > diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
> > index 34742c6e189e..f17c4c03db30 100644
> > --- a/drivers/xen/xlate_mmu.c
> > +++ b/drivers/xen/xlate_mmu.c
> > @@ -261,7 +261,6 @@ int __init xen_xlate_map_ballooned_pages(xen_pfn_t
> > **gfns, void **virt,
> >     	return 0;
> >   }
> > -EXPORT_SYMBOL_GPL(xen_xlate_map_ballooned_pages);
> >     struct remap_pfn {
> >   	struct mm_struct *mm;
> 
> -- 
> Regards,
> 
> Oleksandr Tyshchenko
>