linux-kernel - Re: [PATCH] PM / Domains: Fix integer overflows on u32 bit multiplies

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Date:   Thu, 18 Mar 2021 19:57:14 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Colin King <colin.king@...onical.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marc Titinger <mtitinger+renesas@...libre.com>,
        Lina Iyer <lina.iyer@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PM / Domains: Fix integer overflows on u32 bit multiplies

On Sun, Feb 7, 2021 at 11:47 PM Colin King <colin.king@...onical.com> wrote:
>
> From: Colin Ian King <colin.king@...onical.com>
>
> There are three occurrances of u32 variables being multiplied by
> 1000 using 32 bit multiplies and the result being assigned to a
> 64 bit signed integer.  These can potentially lead to a 32 bit
> overflows, so fix this by casting 1000 to a UL first to force
> a 64 bit multiply hence avoiding the overflow.
>
> Addresses-Coverity: ("Unintentional integer overflow")
> Fixes: 30f604283e05 ("PM / Domains: Allow domain power states to be read from DT")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/base/power/domain.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index aaf6c83b5cf6..ddeff69126ff 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -2831,10 +2831,10 @@ static int genpd_parse_state(struct genpd_power_state *genpd_state,
>
>         err = of_property_read_u32(state_node, "min-residency-us", &residency);
>         if (!err)
> -               genpd_state->residency_ns = 1000 * residency;
> +               genpd_state->residency_ns = 1000UL * residency;

Wouldn't it be better to use NSEC_PER_USEC here and below?

>
> -       genpd_state->power_on_latency_ns = 1000 * exit_latency;
> -       genpd_state->power_off_latency_ns = 1000 * entry_latency;
> +       genpd_state->power_on_latency_ns = 1000UL * exit_latency;
> +       genpd_state->power_off_latency_ns = 1000UL * entry_latency;
>         genpd_state->fwnode = &state_node->fwnode;
>
>         return 0;
> --
> 2.29.2
>