[PATCH v4 4/5] PCI: generic: Correct, and avoid overflow, in bus_max calculation.

Bjorn Helgaas
2015-10-08T15:02:43Z

[+cc Arnd]

And this one?

On Fri, Oct 02, 2015 at 11:44:02AM -0700, David Daney wrote:
> From: David Daney <david.daney@cavium.com>
>
> There are two problems with the bus_max calculation:
>
> 1) The u8 data type can overflow for large config space windows.
>
> 2) The calculation is incorrect for a bus range that doesn't start at
> zero.
>
> Since the configuration space is relative to bus zero, make bus_max
> just be the size of the config window scaled by bus_shift. Then clamp
> it to a maximum of 255, per PCI. Use a data type of int to avoid
> overflow problems.
>
> Update host-generic-pci.txt to clarify the semantics of the "reg"
> property with respect to non-zero starting bus numbers.
>
> Signed-off-by: David Daney <david.daney@cavium.com>
> ---
> Change from V3: Add to explanation of "reg" property in
> host-generic-pci.txt. Add error message if "reg" property is too big.
>
> Documentation/devicetree/bindings/pci/host-generic-pci.txt | 6 +++++-
> drivers/pci/host/pci-host-generic.c | 12 +++++++++---
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/pci/host-generic-pci.txt b/Documentation/devicetree/bindings/pci/host-generic-pci.txt
> index cf3e205..42303bb 100644
> --- a/Documentation/devicetree/bindings/pci/host-generic-pci.txt
> +++ b/Documentation/devicetree/bindings/pci/host-generic-pci.txt
> @@ -34,7 +34,11 @@ Properties of the host controller node:
> - #size-cells : Must be 2.
>
> - reg : The Configuration Space base address and size, as accessed
> - from the parent bus.
> + from the parent bus. The base address corresponds to
> + bus zero, even though the "bus-range" property may specify
> + a different starting bus number. The driver must only map
> + or access the portion of the Configuration Space that
> + corresponds to the "bus-range"
>
>
> Properties of the /chosen node:
> diff --git a/drivers/pci/host/pci-host-generic.c b/drivers/pci/host/pci-host-generic.c
> index 216ded5..5cce837 100644
> --- a/drivers/pci/host/pci-host-generic.c
> +++ b/drivers/pci/host/pci-host-generic.c
> @@ -164,7 +164,7 @@ out_release_res:
> static int gen_pci_parse_map_cfg_windows(struct gen_pci *pci)
> {
> int err;
> - u8 bus_max;
> + int bus_max;
> resource_size_t busn;
> struct resource *bus_range;
> struct device *dev = pci->host.dev.parent;
> @@ -177,8 +177,14 @@ static int gen_pci_parse_map_cfg_windows(struct gen_pci *pci)
> }
>
> /* Limit the bus-range to fit within reg */
> - bus_max = pci->cfg.bus_range->start +
> - (resource_size(&pci->cfg.res) >> pci->cfg.ops->bus_shift) - 1;
> + bus_max = (resource_size(&pci->cfg.res) >> pci->cfg.ops->bus_shift) - 1;
> + if (bus_max > 255) {
> + dev_err(dev,
> + "\"reg\" size corresponds to bus %d, truncating to 255\n",
> + bus_max);
> + bus_max = 255;
> + }
> +
> pci->cfg.bus_range->end = min_t(resource_size_t,
> pci->cfg.bus_range->end, bus_max);
>
> --
> 1.9.1
>
> --
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