Re: [PATCH] cpufreq: intel_pstate: fix possible integer overflow

[Dirk Brandewie]

On 10/21/2013 03:47 PM, Rafael J. Wysocki wrote:
> 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@xxxxxxxxx>
> > Acked-by: Dirk Brandewie <dirk.j.brandewie@xxxxxxxxx>
>
> Actually, isn't (pstate << 8) guaranteed not to overflow?

Yes, I was assuming this was caught by a static checking tool. I
didn't see a downside to giving the compilier complete information.

> > > ---
> > >    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;

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