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

Damien Le Moal
2022-06-14T08:23:48Z

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@baikalelectronics.ru>
> Reviewed-by: Hannes Reinecke <hare@suse.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