RE: [PATCH] Enable SR-IOV instantiation through /sys file

[Wang, Liang-min]

> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> Sent: Tuesday, October 24, 2017 6:07 PM
> To: Wang, Liang-min <liang-min.wang@xxxxxxxxx>
> Cc: Kirsher, Jeffrey T <jeffrey.t.kirsher@xxxxxxxxx>; kvm@xxxxxxxxxxxxxxx;
> linux-pci@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> bhelgaas@xxxxxxxxxx; Duyck, Alexander H <alexander.h.duyck@xxxxxxxxx>
> Subject: Re: [PATCH] Enable SR-IOV instantiation through /sys file
> 
> On Tue, 24 Oct 2017 21:49:15 +0000
> "Wang, Liang-min" <liang-min.wang@xxxxxxxxx> wrote:
> 
> > Just like any PCIe devices that supports SR-IOV. There are restrictions set for
> VF. Also, there is a concept of trust VF now available for PF to manage certain
> features that only selected VF could exercise. Are you saying all the devices
> supporting SR-IOV all have security issue?
> 
> Here's a simple example, most SR-IOV capable NICs, including those from
> Intel, require the PF interface to be up in order to route traffic from
> the VF.  If the user controls the PF interface and VFs are used
> elsewhere in the host, the PF driver in userspace can induce a denial
> of service on the VFs.  That doesn't even take into account that VFs
> might be in separate IOMMU groups from the PF and therefore not
> isolated from the host like the PF and that the PF driver can
> potentially manipulate the VF, possibly performing DMA on behalf of the
> PF.  VFs are only considered secure today because the PF is managed by
> a driver in the host kernel.  Allowing simple enablement of VFs for a
> user owned PF seems inherently insecure to me.  Thanks,
> 
> Alex

Firstly, the concern is on user-space PF driver based upon vfio-pci, this patch doesn't
change PF behavior so with/without this patch, the concern remains the same.
Secondly, the security concern (including denial of service) in general is to ensure trust
entity to be trust-worthy. No matter the PF driver is in kernel-space or in user- space,
necessary mechanism needs to be enforced on the device driver to ensure it's
trusted worthy. For example, ixgbe kernel driver introduces a Tx hang detection
to avoid driver stays in a bad state. Therefore, it's the responsibility of user-space
driver function, which based upon vfio-pci, to enforce necessary mechanism to ensure
its trust-ness. That's a given.