[PATCH] ARM: fix get_user() broken with veneer

[Masahiro Yamada]

On Fri, Jul 19, 2024 at 2:10 AM John Stultz <jstultz at google.com> wrote:
>
> On Tue, Sep 26, 2023 at 9:09 AM Masahiro Yamada <masahiroy at kernel.org> wrote:
> >
> > The 32-bit ARM kernel stops working if the kernel grows to the point
> > where veneers for __get_user_* are created.
> >
> > AAPCS32 [1] states, "Register r12 (IP) may be used by a linker as a
> > scratch register between a routine and any subroutine it calls. It
> > can also be used within a routine to hold intermediate values between
> > subroutine calls."
> >
> > However, bl instructions buried within the inline asm are unpredictable
> > for compilers; hence, "ip" must be added to the clobber list.
> >
> > This becomes critical when veneers for __get_user_* are created because
> > veneers use the ip register since commit 02e541db0540 ("ARM: 8323/1:
> > force linker to use PIC veneers").
> >
> > [1]: https://github.com/ARM-software/abi-aa/blob/2023Q1/aapcs32/aapcs32.rst
> >
> > Signed-off-by: Masahiro Yamada <masahiroy at kernel.org>
> > Reviewed-by: Ard Biesheuvel <ardb at kernel.org>
>
> + stable at vger.kernel.org
> It seems like this (commit 24d3ba0a7b44c1617c27f5045eecc4f34752ab03
> upstream) would be a good candidate for -stable?


Yes.

This one should be back-ported. Thanks.






--
Best Regards
Masahiro Yamada