linux-kernel - Re: [PATCH] cpufreq: intel_pstate: fix possible integer overflow

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Date:	Tue, 22 Oct 2013 00:47:18 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Dirk Brandewie <dirk.brandewie@...il.com>
Cc:	"Geyslan G. Bem" <geyslan@...il.com>, kernel-br@...glegroups.com,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"open list:CPU FREQUENCY DRI..." <cpufreq@...r.kernel.org>,
	"open list:CPU FREQUENCY DRI..." <linux-pm@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: intel_pstate: fix possible integer overflow

On Monday, October 21, 2013 08:56:22 AM Dirk Brandewie wrote:
> On 10/19/2013 08:31 PM, Geyslan G. Bem wrote:
> > The expression 'pstate << 8' is evaluated using 32-bit arithmetic while
> > 'val' expects an expression of type u64.
> >
> > Signed-off-by: Geyslan G. Bem <geyslan@...il.com>
> Acked-by: Dirk Brandewie <dirk.j.brandewie@...el.com>

Actually, isn't (pstate << 8) guaranteed not to overflow?

> > ---
> >   drivers/cpufreq/intel_pstate.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> > index badf620..43446b5 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -395,7 +395,7 @@ static void intel_pstate_set_pstate(struct cpudata *cpu, int pstate)
> >   	trace_cpu_frequency(pstate * 100000, cpu->cpu);
> >
> >   	cpu->pstate.current_pstate = pstate;
> > -	val = pstate << 8;
> > +	val = (u64)pstate << 8;
> >   	if (limits.no_turbo)
> >   		val |= (u64)1 << 32;
> >
> >
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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