linux-kernel - Re: [PATCH] ARM: fix get

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Message-ID: <CAK7LNAT3WQ+3K+Z=ueZ4f_1EF29aPui-HS2eV3erSb9rHJSPLA@mail.gmail.com>
Date: Fri, 19 Jul 2024 12:04:39 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: John Stultz <jstultz@...gle.com>
Cc: patches@...linux.org.uk, linux-kernel@...r.kernel.org, 
	Russell King <linux@...linux.org.uk>, Ard Biesheuvel <ardb@...nel.org>, 
	linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org, 
	Neill Kapron <nkapron@...gle.com>
Subject: Re: [PATCH] ARM: fix get_user() broken with veneer

On Fri, Jul 19, 2024 at 2:10 AM John Stultz <jstultz@...gle.com> wrote:
>
> On Tue, Sep 26, 2023 at 9:09 AM Masahiro Yamada <masahiroy@...nel.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@...nel.org>
> > Reviewed-by: Ard Biesheuvel <ardb@...nel.org>
>
> + stable@...r.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