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

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Message-ID: <CAJZ5v0gHgfscDCGo3P5JVn73uUTBkpfCqRJV3QcOnFt8FP7FhQ@mail.gmail.com>
Date:   Tue, 21 Nov 2023 20:56:35 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Nikita Kiryushin <kiryushin@...ud.ru>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        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 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.  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
>