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From: Guenter Roeck <groeck@google.com>
To: Colin King <colin.king@canonical.com>
Cc: "open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	David Airlie <airlied@linux.ie>,
	kernel-janitors@vger.kernel.org, Sandy Huang <hjc@rock-chips.com>,
	Maling list - DRI developers <dri-devel@lists.freedesktop.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Guenter Roeck <groeck@chromium.org>,
	Sean Paul <seanpaul@chromium.org>,
	Chris Zhong <zyw@rock-chips.com>,
	"moderated list:ARM PORT" <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] drm/rockchip: cdn-dp: fix sign extension on an int multiply for a u64 result
Date: Tue, 15 Sep 2020 17:29:39 +0000	[thread overview]
Message-ID: <CABXOdTcnAzFh81GuJ0Niqu6t2pF5AmwgFoXHf766XcXct_F+5g@mail.gmail.com> (raw)
In-Reply-To: <20200915162049.36434-1-colin.king@canonical.com>

On Tue, Sep 15, 2020 at 9:20 AM Colin King <colin.king@canonical.com> wrote:
>
> From: Colin Ian King <colin.king@canonical.com>
>
> The variable bit_per_pix is a u8 and is promoted in the multiplication
> to an int type and then sign extended to a u64. If the result of the
> int multiplication is greater than 0x7fffffff then the upper 32 bits will
> be set to 1 as a result of the sign extension. Avoid this by casting
> tu_size_reg to u64 to avoid sign extension and also a potential overflow.
>
> Addresses-Coverity: ("Unintended sign extension")
> Fixes: 1a0f7ed3abe2 ("drm/rockchip: cdn-dp: add cdn DP support for rk3399")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>

Reviewed-by: Guenter Roeck <groeck@chromium.org>

> ---
>  drivers/gpu/drm/rockchip/cdn-dp-reg.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/rockchip/cdn-dp-reg.c b/drivers/gpu/drm/rockchip/cdn-dp-reg.c
> index 9d2163ef4d6e..33fb4d05c506 100644
> --- a/drivers/gpu/drm/rockchip/cdn-dp-reg.c
> +++ b/drivers/gpu/drm/rockchip/cdn-dp-reg.c
> @@ -658,7 +658,7 @@ int cdn_dp_config_video(struct cdn_dp_device *dp)
>          */
>         do {
>                 tu_size_reg += 2;
> -               symbol = tu_size_reg * mode->clock * bit_per_pix;
> +               symbol = (u64)tu_size_reg * mode->clock * bit_per_pix;
>                 do_div(symbol, dp->max_lanes * link_rate * 8);
>                 rem = do_div(symbol, 1000);
>                 if (tu_size_reg > 64) {
> --
> 2.27.0
>

  reply	other threads:[~2020-09-15 17:29 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 16:20 [PATCH] drm/rockchip: cdn-dp: fix sign extension on an int multiply for a u64 result Colin King
2020-09-15 17:29 ` Guenter Roeck [this message]
2021-05-28 18:55 ` Heiko Stuebner

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