linux-kernel - Re: [PATCH v3 2/5] vfio/pci: Add device denylist

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Date:   Thu, 23 Jul 2020 16:41:26 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Giovanni Cabiddu <giovanni.cabiddu@...el.com>
Cc:     herbert@...dor.apana.org.au, cohuck@...hat.com, nhorman@...hat.com,
        vdronov@...hat.com, bhelgaas@...gle.com, mark.a.chambers@...el.com,
        gordon.mcfadden@...el.com, ahsan.atta@...el.com,
        fiona.trahe@...el.com, qat-linux@...el.com, kvm@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] vfio/pci: Add device denylist

On Thu, 23 Jul 2020 22:47:02 +0100
Giovanni Cabiddu <giovanni.cabiddu@...el.com> wrote:

> Add denylist of devices that by default are not probed by vfio-pci.
> Devices in this list may be susceptible to untrusted application, even
> if the IOMMU is enabled. To be accessed via vfio-pci, the user has to
> explicitly disable the denylist.
> 
> The denylist can be disabled via the module parameter disable_denylist.
> 
> Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@...el.com>
> ---
>  drivers/vfio/pci/vfio_pci.c | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 7c0779018b1b..673f53c4798e 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -60,6 +60,10 @@ module_param(enable_sriov, bool, 0644);
>  MODULE_PARM_DESC(enable_sriov, "Enable support for SR-IOV configuration.  Enabling SR-IOV on a PF typically requires support of the userspace PF driver, enabling VFs without such support may result in non-functional VFs or PF.");
>  #endif
>  
> +static bool disable_denylist;
> +module_param(disable_denylist, bool, 0444);
> +MODULE_PARM_DESC(disable_denylist, "Disable use of device denylist. Disabling the denylist prevents binding to devices with known errata that may lead to exploitable stability or security issues when accessed by untrusted users.");

s/prevents/allows/

ie. the denylist prevents binding, therefore disabling the denylist
allows binding

I can fix this on commit without a new version if you agree.  I also
see that patch 1/5 didn't change since v2, so I'll transfer Bjorn's
ack.  If that sounds good I'll queue the first 3 patches in my next
branch for v5.9.  Thanks,

Alex

> +
>  static inline bool vfio_vga_disabled(void)
>  {
>  #ifdef CONFIG_VFIO_PCI_VGA
> @@ -69,6 +73,29 @@ static inline bool vfio_vga_disabled(void)
>  #endif
>  }
>  
> +static bool vfio_pci_dev_in_denylist(struct pci_dev *pdev)
> +{
> +	return false;
> +}
> +
> +static bool vfio_pci_is_denylisted(struct pci_dev *pdev)
> +{
> +	if (!vfio_pci_dev_in_denylist(pdev))
> +		return false;
> +
> +	if (disable_denylist) {
> +		pci_warn(pdev,
> +			 "device denylist disabled - allowing device %04x:%04x.\n",
> +			 pdev->vendor, pdev->device);
> +		return false;
> +	}
> +
> +	pci_warn(pdev, "%04x:%04x exists in vfio-pci device denylist, driver probing disallowed.\n",
> +		 pdev->vendor, pdev->device);
> +
> +	return true;
> +}
> +
>  /*
>   * Our VGA arbiter participation is limited since we don't know anything
>   * about the device itself.  However, if the device is the only VGA device
> @@ -1847,6 +1874,9 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	struct iommu_group *group;
>  	int ret;
>  
> +	if (vfio_pci_is_denylisted(pdev))
> +		return -EINVAL;
> +
>  	if (pdev->hdr_type != PCI_HEADER_TYPE_NORMAL)
>  		return -EINVAL;
>  
> @@ -2336,6 +2366,9 @@ static int __init vfio_pci_init(void)
>  
>  	vfio_pci_fill_ids();
>  
> +	if (disable_denylist)
> +		pr_warn("device denylist disabled.\n");
> +
>  	return 0;
>  
>  out_driver: