linux-kernel - Re: [PATCH] drm/stm: ltdc: limit number of layer to avoid memory overflow

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Date:   Fri, 5 Apr 2019 16:30:10 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Yannick FERTRE <yannick.fertre@...com>,
        Benjamin GAIGNARD <benjamin.gaignard@...com>,
        Vincent ABRIOU <vincent.abriou@...com>,
        "David Airlie" <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/stm: ltdc: limit number of layer to avoid memory
 overflow

Dear Yannick,
Thank you for your patch,

Acked-by: Philippe Cornu <philippe.cornu@...com>

Philippe :)

On 4/3/19 11:20 AM, Yannick Fertré wrote:
> If the number of layer is greater than LTDC_MAX_LAYER, we can have
> memory overflow when reading plane_fpsi[].
> 
> Signed-off-by: Yannick Fertré <yannick.fertre@...com>
> ---
>   drivers/gpu/drm/stm/ltdc.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
> index 32fd6a3..05bd4b6 100644
> --- a/drivers/gpu/drm/stm/ltdc.c
> +++ b/drivers/gpu/drm/stm/ltdc.c
> @@ -1021,10 +1021,13 @@ static int ltdc_get_caps(struct drm_device *ddev)
>   	struct ltdc_device *ldev = ddev->dev_private;
>   	u32 bus_width_log2, lcr, gc2r;
>   
> -	/* at least 1 layer must be managed */
> +	/*
> +	 * at least 1 layer must be managed & the number of layers
> +	 * must not exceed LTDC_MAX_LAYER
> +	 */
>   	lcr = reg_read(ldev->regs, LTDC_LCR);
>   
> -	ldev->caps.nb_layers = max_t(int, lcr, 1);
> +	ldev->caps.nb_layers = clamp((int)lcr, 1, LTDC_MAX_LAYER);
>   
>   	/* set data bus width */
>   	gc2r = reg_read(ldev->regs, LTDC_GC2R);
>