linux-kernel - Re: [PATCH] powercap: intel_rapl: fix UBSAN shift-out-of-bounds issue

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Date:   Wed, 21 Sep 2022 20:17:34 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     chao.qin@...el.com
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        paul.mei@...el.com, lili.li@...el.com
Subject: Re: [PATCH] powercap: intel_rapl: fix UBSAN shift-out-of-bounds issue

On Tue, Sep 20, 2022 at 8:19 AM <chao.qin@...el.com> wrote:
>
> From: Chao Qin <chao.qin@...el.com>
>
> When value < time_unit, the parameter of ilog2() will be zero and
> the return value is -1. u64(-1) is too large for shift exponent
> and then will trigger shift-out-of-bounds:
>
> shift exponent 18446744073709551615 is too large for 32-bit type 'int'
> Call Trace:
>  rapl_compute_time_window_core
>  rapl_write_data_raw
>  set_time_window
>  store_constraint_time_window_us
>
> Signed-off-by: Chao Qin <chao.qin@...el.com>
> Acked-by: Zhang Rui <rui.zhang@...el.com>
> ---
>  drivers/powercap/intel_rapl_common.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/powercap/intel_rapl_common.c b/drivers/powercap/intel_rapl_common.c
> index 21d624f9f5fb..bf91248630c3 100644
> --- a/drivers/powercap/intel_rapl_common.c
> +++ b/drivers/powercap/intel_rapl_common.c
> @@ -994,6 +994,9 @@ static u64 rapl_compute_time_window_core(struct rapl_package *rp, u64 value,
>                 y = value & 0x1f;
>                 value = (1 << y) * (4 + f) * rp->time_unit / 4;
>         } else {
> +               if (value < rp->time_unit)
> +                       return 0;
> +
>                 do_div(value, rp->time_unit);
>                 y = ilog2(value);
>                 f = div64_u64(4 * (value - (1 << y)), 1 << y);
> --

Applied as 6.1 material, thanks!