linux-kernel - Re: [PATCH v4 08/23] ata: libahci_platform: Sanity check the DT child nodes number

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Date:   Tue, 14 Jun 2022 17:23:33 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Hans de Goede <hdegoede@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.de>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Rob Herring <robh+dt@...nel.org>, linux-ide@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 08/23] ata: libahci_platform: Sanity check the DT child
 nodes number

On 6/10/22 17:17, Serge Semin wrote:
> Having greater than AHCI_MAX_PORTS (32) ports detected isn't that critical
> from the further AHCI-platform initialization point of view since
> exceeding the ports upper limit will cause allocating more resources than
> will be used afterwards. But detecting too many child DT-nodes doesn't
> seem right since it's very unlikely to have it on an ordinary platform. In
> accordance with the AHCI specification there can't be more than 32 ports
> implemented at least due to having the CAP.NP field of 5 bits wide and the
> PI register of dword size. Thus if such situation is found the DTB must
> have been corrupted and the data read from it shouldn't be reliable. Let's
> consider that as an erroneous situation and halt further resources
> allocation.
> 
> Note it's logically more correct to have the nports set only after the
> initialization value is checked for being sane. So while at it let's make
> sure nports is assigned with a correct value.
> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> Reviewed-by: Hannes Reinecke <hare@...e.de>
> 
> ---
> 
> Changelog v2:
> - Drop the else word from the child_nodes value checking if-else-if
>   statement (@Damien) and convert the after-else part into the ternary
>   operator-based statement.
> 
> Changelog v4:
> - Fix some logical mistakes in the patch log. (@Sergei Shtylyov)
> ---
>  drivers/ata/libahci_platform.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/ata/libahci_platform.c b/drivers/ata/libahci_platform.c
> index 814804582d1d..8aed7b29c7ab 100644
> --- a/drivers/ata/libahci_platform.c
> +++ b/drivers/ata/libahci_platform.c
> @@ -451,15 +451,22 @@ struct ahci_host_priv *ahci_platform_get_resources(struct platform_device *pdev,
>  		}
>  	}
>  
> -	hpriv->nports = child_nodes = of_get_child_count(dev->of_node);
> +	/*
> +	 * Too many sub-nodes most likely means having something wrong with
> +	 * the firmware.
> +	 */
> +	child_nodes = of_get_child_count(dev->of_node);
> +	if (child_nodes > AHCI_MAX_PORTS) {
> +		rc = -EINVAL;
> +		goto err_out;
> +	}
>  
>  	/*
>  	 * If no sub-node was found, we still need to set nports to
>  	 * one in order to be able to use the
>  	 * ahci_platform_[en|dis]able_[phys|regulators] functions.
>  	 */
> -	if (!child_nodes)
> -		hpriv->nports = 1;
> +	hpriv->nports = child_nodes ?: 1;

This change is not necessary and makes the code far less easy to read.

>  
>  	hpriv->phys = devm_kcalloc(dev, hpriv->nports, sizeof(*hpriv->phys), GFP_KERNEL);
>  	if (!hpriv->phys) {


-- 
Damien Le Moal
Western Digital Research