From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave.Martin@arm.com (Dave Martin)
Date: Tue, 25 Jul 2017 14:25:15 +0100
Subject: [PATCH] arm64: sysreg: Fix unprotected macro argmuent in
 write_sysreg
In-Reply-To: <20170725130849.GA8358@leverpostej>
References: <1500983561-5723-1-git-send-email-Dave.Martin@arm.com>
 <20170725130849.GA8358@leverpostej>
Message-ID: <20170725132515.GC6321@e103592.cambridge.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, Jul 25, 2017 at 02:08:51PM +0100, Mark Rutland wrote:
> On Tue, Jul 25, 2017 at 12:52:41PM +0100, Dave Martin wrote:
> > write_sysreg() may misparse the value argument because it is used
> > without parentheses to protect it.
> > 
> > This patch adds the ( ) in order to avoid any surprises.
> > 
> > Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> > ---
> >  arch/arm64/include/asm/sysreg.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> > index 16e44fa..822eebc 100644
> > --- a/arch/arm64/include/asm/sysreg.h
> > +++ b/arch/arm64/include/asm/sysreg.h
> > @@ -492,7 +492,7 @@ asm(
> >   * the "%x0" template means XZR.
> >   */
> >  #define write_sysreg(v, r) do {					\
> > -	u64 __val = (u64)v;					\
> > +	u64 __val = (u64)(v);					\
> >  	asm volatile("msr " __stringify(r) ", %x0"		\
> >  		     : : "rZ" (__val));				\
> >  } while (0)
> 
> Looks sensible.
> 
> It looks like write_sysreg_s() will need the same fixup; could you do
> that too?
> 
> With that:
> 
> Acked-by: Mark Rutland <mark.rutland@arm.com>

Agreed, especially if somebody else does it...

Note that there are some

	write_sysreg(1 << n, SYS_FOO)

whose parse will be changed by this.  However, n <= 30 in every case
I've found, which should mean there is no change to the result -- i.e.,
(u64)((int)1 << n) == (u64)1 << n if n <= 30.

Cheers
---Dave