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

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Message-ID: <2024072348-perfectly-duct-e0aa@gregkh>
Date: Tue, 23 Jul 2024 15:15:56 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: John Stultz <jstultz@...gle.com>, 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 12:04:39PM +0900, Masahiro Yamada wrote:
> 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.

Now queued up, thanks.

greg k-h