Re: [PATCH] ACPI: LPIT: fix u32 multiplication overflow

[Rafael J. Wysocki]

On Thu, Nov 9, 2023 at 7:09 PM Nikita Kiryushin <kiryushin@xxxxxxxx> 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.  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@xxxxxxxx>
> ---
>   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
>