From: Alexander Kurz <akurz@blala.de>
To: Sascha Hauer <s.hauer@pengutronix.de>
Cc: barebox@lists.infradead.org, Uwe Kleine-Koenig <ukl@pengutronix.de>
Subject: Re: [PATCH] arm/cpu/lowlevel: fix: possible processor mode change
Date: Fri, 4 Mar 2016 09:43:56 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.00.1603040843140.23083@blala.de> (raw)
In-Reply-To: <20160304070448.GB21869@pengutronix.de>
Hi Sascha,
I stumbled across this while starting a barebox image uploaded via
JTAG to RAM onto an old Olimex EP9302 demo board which eventually
ran into abort mode (unrelated to barebox).
Anyway, this fix might affect any ARM target/board.
I do not have a good example, when barebox might get started by some
platform in mode != supervisor, but even though - barebox should be
perpared for this.
Thanks, Alexander
On Fri, 4 Mar 2016, Sascha Hauer wrote:
> Hi Alexander,
>
> On Wed, Mar 02, 2016 at 11:51:28PM +0100, Alexander Kurz wrote:
> > This is a re-application of fix 17644b55.
> > arm_cpu_lowlevel_init() will set the processor mode to 0x13 (supervisor).
> > When this function is entered via a different processor mode, register
> > banking will happen to lr (r14), resulting in an invalid return address.
> > This fix will preserve the return address manually.
> >
> > Signed-off-by: Alexander Kurz <akurz@blala.de>
> > ---
> > arch/arm/cpu/lowlevel.S | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/cpu/lowlevel.S b/arch/arm/cpu/lowlevel.S
> > index b76222d..e5baa12 100644
> > --- a/arch/arm/cpu/lowlevel.S
> > +++ b/arch/arm/cpu/lowlevel.S
> > @@ -4,6 +4,8 @@
> >
> > .section ".text_bare_init_","ax"
> > ENTRY(arm_cpu_lowlevel_init)
> > + /* save lr, since it may be banked away with a processor mode change */
> > + mov r2, lr
>
> Thanks for fixing this and for adding a comment why this is done. This
> hopefully prevents us from breaking it again.
>
> Out of interest, what system are you using where this fix is necesssary?
>
> Uwe, now we know why that was done and why e190bcf (arm/cpu/lowlevel:
> Don't save the return address in another register) was a bad idea.
>
> Applied this one to master.
>
> Sascha
>
> --
> Pengutronix e.K. | |
> Industrial Linux Solutions | http://www.pengutronix.de/ |
> Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
> Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
>
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next prev parent reply other threads:[~2016-03-04 8:45 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-02 22:51 Alexander Kurz
2016-03-04 7:04 ` Sascha Hauer
2016-03-04 7:15 ` Uwe Kleine-König
2016-03-04 8:43 ` Alexander Kurz [this message]
2016-03-04 9:18 ` Uwe Kleine-König
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