linux-kernel - Re: [PATCH] ACPI: LPIT: fix u32 multiplication overflow

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Date:   Tue, 21 Nov 2023 21:14:48 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Nikita Kiryushin <kiryushin@...ud.ru>
Cc:     Len Brown <lenb@...nel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        lvc-project@...uxtesting.org
Subject: Re: [PATCH] ACPI: LPIT: fix u32 multiplication overflow

On Tue, Nov 21, 2023 at 8:56 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Nov 9, 2023 at 7:09 PM Nikita Kiryushin <kiryushin@...ud.ru> wrote:
> >
> > In lpit_update_residency there is a possibility of overflow
> > in multiplication, if tsc_khz is large enough (> UINT_MAX/1000).
>
> That would be a TSC ticking at hundreds of millions of kHz if I'm not
> mistaken.

That should be "hundreds of thousands of kHz", so I was mistaken.

But anyway:

> Why is it really a concern?
>
> > Change multiplication to mul_u32_u32.
>
> So why is this better?
>
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> >
> > Fixes: eeb2d80d502a ("ACPI / LPIT: Add Low Power Idle Table (LPIT) support")
> > Signed-off-by: Nikita Kiryushin <kiryushin@...ud.ru>
> > ---
> >   drivers/acpi/acpi_lpit.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/acpi/acpi_lpit.c b/drivers/acpi/acpi_lpit.c
> > index c5598b6d5db8..794962c5c88e 100644
> > --- a/drivers/acpi/acpi_lpit.c
> > +++ b/drivers/acpi/acpi_lpit.c
> > @@ -105,7 +105,7 @@ static void lpit_update_residency(struct
> > lpit_residency_info *info,
> >                 return;
> >         info->frequency = lpit_native->counter_frequency ?
> > -                               lpit_native->counter_frequency : tsc_khz * 1000;
> > +                               lpit_native->counter_frequency : mul_u32_u32(tsc_khz, 1000U);
> >         if (!info->frequency)
> >                 info->frequency = 1;
> >   -- 2.34.1
> >