linux-kernel - Re: drm/komeda: Fix potential integer overflow in komeda_crtc_update_clock

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Date:   Mon, 12 Aug 2019 10:18:11 +0000
From:   "james qian wang (Arm Technology China)" <james.qian.wang@....com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
CC:     Liviu Dudau <Liviu.Dudau@....com>,
        Brian Starkey <Brian.Starkey@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        nd <nd@....com>
Subject: Re: drm/komeda: Fix potential integer overflow in
 komeda_crtc_update_clock_ratio

On Sun, Aug 11, 2019 at 07:08:01PM -0500, Gustavo A. R. Silva wrote:
> Add suffix ULL to constant 1000 in order to avoid a potential integer
> overflow and give the compiler complete information about the proper
> arithmetic to use. Notice that this constant is being used in a context
> that expects an expression of type u64, but it's currently evaluated
> using 32-bit arithmetic.
> 
> Addresses-Coverity-ID: 1485796 ("Unintentional integer overflow")
> Fixes: ed22c6d9304d ("drm/komeda: Use drm_display_mode "crtc_" prefixed hardware timings")
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/gpu/drm/arm/display/komeda/komeda_crtc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> index fa9a4593bb37..624d257da20f 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_crtc.c
> @@ -27,7 +27,7 @@ static void komeda_crtc_update_clock_ratio(struct komeda_crtc_state *kcrtc_st)
>  		return;
>  	}
>  
> -	pxlclk = kcrtc_st->base.adjusted_mode.crtc_clock * 1000;
> +	pxlclk = kcrtc_st->base.adjusted_mode.crtc_clock * 1000ULL;
>  	aclk = komeda_crtc_get_aclk(kcrtc_st);
>  
>  	kcrtc_st->clock_ratio = div64_u64(aclk << 32, pxlclk);

Thank you for the patch.

Reviewed-by: James Qian Wang (Arm Technology China) <james.qian.wang@....com>