Re: [PATCH v3] PCI: ACPI: Support Microsoft's "DmaProperty"

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Feb 16, 2022 at 02:05:41PM -0800, Rajat Jain wrote:
> The "DmaProperty" is supported and documented by Microsoft here:
> https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports
> They use this property for DMA protection:
> https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt
> 
> Support the "DmaProperty" with the same semantics. Windows documents the
> property to apply to PCIe root ports only. Extend it to apply to any
> PCI device. This is useful for internal PCI devices that do not hang off
> a PCIe rootport, but offer an attack surface for DMA attacks (e.g.
> internal network devices).
> 
> Signed-off-by: Rajat Jain <rajatja@google.com>
> ---
> v3: * Use Microsoft's documented property "DmaProperty"
>     * Resctrict to ACPI only
> 
>  drivers/pci/pci-acpi.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index a42dbf448860..660baa60c040 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1350,12 +1350,30 @@ static void pci_acpi_set_external_facing(struct pci_dev *dev)
>  		dev->external_facing = 1;
>  }
>  
> +static void pci_acpi_check_for_dma_protection(struct pci_dev *dev)
> +{
> +	u8 val;
> +
> +	/*
> +	 * Microsoft Windows uses this property, and is documented here:
> +	 * https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports
> +	 * While Microsoft documents this property as only applicable to PCIe
> +	 * root ports, we expand it to be applicable to any PCI device.
> +	 */
> +	if (device_property_read_u8(&dev->dev, "DmaProperty", &val))
> +		return;

Why not continue to only do this for PCIe devices like it is actually
being used for?  Why expand it?

And what driver/device is going to use this?

thanks,

greg k-h