linux-kernel - Re: [PATCH] drm/msm/dsi: prevent unintentional integer overflow in dsi_pll_28nm_clk_recalc

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Date:   Sat, 2 Oct 2021 01:44:38 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Tim Gardner <tim.gardner@...onical.com>,
        dri-devel@...ts.freedesktop.org
Cc:     Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dsi: prevent unintentional integer overflow in
 dsi_pll_28nm_clk_recalc_rate()

On 29/09/2021 20:51, Tim Gardner wrote:
> Coverity warns of an unintentional integer overflow
> 
> CID 120715 (#1 of 1): Unintentional integer overflow (OVERFLOW_BEFORE_WIDEN)
> overflow_before_widen: Potentially overflowing expression ref_clk * sdm_byp_div
>    with type unsigned int (32 bits, unsigned) is evaluated using 32-bit arithmetic,
>    and then used in a context that expects an expression of type unsigned long
>    (64 bits, unsigned).
> To avoid overflow, cast either ref_clk or sdm_byp_div to type unsigned long.
> 263                vco_rate = ref_clk * sdm_byp_div;
> 
> Fix this and another possible overflow by casting ref_clk to unsigned long.

Changing ref_clk from u32 to unsigned long would be a more simple and 
elegant way of fixing this issue. Could you please update your patch?

> 
> Cc: Rob Clark <robdclark@...il.com>
> Cc: Sean Paul <sean@...rly.run>
> Cc: David Airlie <airlied@...ux.ie>
> Cc: Daniel Vetter <daniel@...ll.ch>
> Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Cc: Abhinav Kumar <abhinavk@...eaurora.org>
> Cc: linux-arm-msm@...r.kernel.org
> Cc: dri-devel@...ts.freedesktop.org
> Cc: freedreno@...ts.freedesktop.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
> ---
>   drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c
> index 2da673a2add6..cfe4b30eb96d 100644
> --- a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c
> +++ b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_28nm.c
> @@ -260,7 +260,7 @@ static unsigned long dsi_pll_28nm_clk_recalc_rate(struct clk_hw *hw,
>   		sdm_byp_div = FIELD(
>   				dsi_phy_read(base + REG_DSI_28nm_PHY_PLL_SDM_CFG0),
>   				DSI_28nm_PHY_PLL_SDM_CFG0_BYP_DIV) + 1;
> -		vco_rate = ref_clk * sdm_byp_div;
> +		vco_rate = (unsigned long)ref_clk * sdm_byp_div;
>   	} else {
>   		/* sdm mode */
>   		sdm_dc_off = FIELD(
> @@ -274,7 +274,7 @@ static unsigned long dsi_pll_28nm_clk_recalc_rate(struct clk_hw *hw,
>   		sdm_freq_seed = (sdm3 << 8) | sdm2;
>   		DBG("sdm_freq_seed = %d", sdm_freq_seed);
>   
> -		vco_rate = (ref_clk * (sdm_dc_off + 1)) +
> +		vco_rate = ((unsigned long)ref_clk * (sdm_dc_off + 1)) +
>   			mult_frac(ref_clk, sdm_freq_seed, BIT(16));
>   		DBG("vco rate = %lu", vco_rate);
>   	}
> 


-- 
With best wishes
Dmitry