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.
Fixes: 243848fc018c ("xen/grant-table: Move xlated_setup_gnttab_pages to common place")
Reported-by: Stephen Rothwell <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>
---
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;
--
2.32.0
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 <[email protected]>
> Signed-off-by: Masahiro Yamada <[email protected]>
I think the patch is correct.
Reviewed-by: Oleksandr Tyshchenko <[email protected]>
> ---
>
> 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
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 <[email protected]>
> > Signed-off-by: Masahiro Yamada <[email protected]>
>
> I think the patch is correct.
>
> Reviewed-by: Oleksandr Tyshchenko <[email protected]>
Acked-by: Stefano Stabellini <[email protected]>
> > ---
> >
> > 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
>
On 06.06.22 06:59, Masahiro Yamada wrote:
> 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.
>
> Fixes: 243848fc018c ("xen/grant-table: Move xlated_setup_gnttab_pages to common place")
> Reported-by: Stephen Rothwell <[email protected]>
> Signed-off-by: Masahiro Yamada <[email protected]>
Pushed to xen/tip.git for-linus-5.19a
Juergen