Re: [PATCH v9 1/5] PCI: Add pcie_get_link_speed() helper for safe array access

[Bjorn Helgaas <helgaas@kernel.org>]

On Sat, Mar 14, 2026 at 12:55:18AM +0800, Hans Zhang wrote:
> The pcie_link_speed[] array is indexed by PCIe generation numbers
> (1 = 2.5 GT/s, 2 = 5 GT/s, ...).  Several drivers use it directly,
> which can lead to out-of-bounds accesses if an invalid generation
> number is used.
> 
> Introduce a helper function pcie_get_link_speed() that returns the
> corresponding enum pci_bus_speed value for a given generation number,
> or PCI_SPEED_UNKNOWN if the generation is out of range.  This will
> allow us to safely handle invalid values after the range check is
> removed from of_pci_get_max_link_speed().
> 
> Signed-off-by: Hans Zhang <18255117159@163.com>
> ---
>  drivers/pci/pci.h   |  2 ++
>  drivers/pci/probe.c | 16 ++++++++++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 13d998fbacce..409aca7d737a 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -108,6 +108,8 @@ struct pcie_tlp_log;
>  				 PCI_EXP_DEVCTL_FERE | PCI_EXP_DEVCTL_URRE)
>  
>  extern const unsigned char pcie_link_speed[];
> +unsigned char pcie_get_link_speed(unsigned int speed);
> +
>  extern bool pci_early_dump;
>  
>  extern struct mutex pci_rescan_remove_lock;
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index bccc7a4bdd79..d6592898330c 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -783,6 +783,22 @@ const unsigned char pcie_link_speed[] = {
>  };
>  EXPORT_SYMBOL_GPL(pcie_link_speed);
>  
> +/**
> + * pcie_link_speed_value - Get speed value from PCIe generation number

Wrong name here (pcie_link_speed_value vs pcie_get_link_speed)
(pointed out by Sashiko).

> + * @speed: PCIe speed (1-based: 1 = 2.5GT, 2 = 5GT, ...)
> + *
> + * Returns the speed value (e.g., PCIE_SPEED_2_5GT) if @speed is valid,
> + * otherwise returns PCI_SPEED_UNKNOWN.
> + */
> +unsigned char pcie_get_link_speed(unsigned int speed)

Sashiko also pointed out that the commit log says this returns "enum
pci_bus_speed", while here we return unsigned char (which is also the
type of pcie_link_speed[x]).

https://sashiko.dev/#/patchset/20260313165522.123518-1-18255117159%40163.com

> +{
> +	if (speed >= ARRAY_SIZE(pcie_link_speed))
> +		return PCI_SPEED_UNKNOWN;
> +
> +	return pcie_link_speed[speed];
> +}
> +EXPORT_SYMBOL_GPL(pcie_get_link_speed);
> +
>  const char *pci_speed_string(enum pci_bus_speed speed)
>  {
>  	/* Indexed by the pci_bus_speed enum */
> -- 
> 2.34.1
>