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From: Cornelia Huck <>
To: Alex Williamson <>
Subject: Re: [PATCH v3 3/7] vfio/pci: Introduce VF token
Date: Thu, 19 Mar 2020 18:27:30 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <158396393244.5601.10297430724964025753.stgit@gimli.home>

On Wed, 11 Mar 2020 15:58:52 -0600
Alex Williamson <> wrote:

> If we enable SR-IOV on a vfio-pci owned PF, the resulting VFs are not
> fully isolated from the PF.  The PF can always cause a denial of service
> to the VF, even if by simply resetting itself.  The degree to which a PF
> can access the data passed through a VF or interfere with its operation
> is dependent on a given SR-IOV implementation.  Therefore we want to
> avoid a scenario where an existing vfio-pci based userspace driver might
> assume the PF driver is trusted, for example assigning a PF to one VM
> and VF to another with some expectation of isolation.  IOMMU grouping
> could be a solution to this, but imposes an unnecessarily strong
> relationship between PF and VF drivers if they need to operate with the
> same IOMMU context.  Instead we introduce a "VF token", which is
> essentially just a shared secret between PF and VF drivers, implemented
> as a UUID.
> The VF token can be set by a vfio-pci based PF driver and must be known
> by the vfio-pci based VF driver in order to gain access to the device.
> This allows the degree to which this VF token is considered secret to be
> determined by the applications and environment.  For example a VM might
> generate a random UUID known only internally to the hypervisor while a
> userspace networking appliance might use a shared, or even well know,
> UUID among the application drivers.
> To incorporate this VF token, the VFIO_GROUP_GET_DEVICE_FD interface is
> extended to accept key=value pairs in addition to the device name.  This
> allows us to most easily deny user access to the device without risk
> that existing userspace drivers assume region offsets, IRQs, and other
> device features, leading to more elaborate error paths.  The format of
> these options are expected to take the form:
> Where the device name is always provided first for compatibility and
> additional options are specified in a space separated list.  The
> relation between and requirements for the additional options will be
> vfio bus driver dependent, however unknown or unused option within this
> schema should return error.  This allow for future use of unknown
> options as well as a positive indication to the user that an option is
> used.
> An example VF token option would take this form:
> "0000:03:00.0 vf_token=2ab74924-c335-45f4-9b16-8569e5b08258"
> When accessing a VF where the PF is making use of vfio-pci, the user
> MUST provide the current vf_token.  When accessing a PF, the user MUST
> provide the current vf_token IF there are active VF users or MAY provide
> a vf_token in order to set the current VF token when no VF users are
> active.  The former requirement assures VF users that an unassociated
> driver cannot usurp the PF device.  These semantics also imply that a
> VF token MUST be set by a PF driver before VF drivers can access their
> device, the default token is random and mechanisms to read the token are
> not provided in order to protect the VF token of previous users.  Use of
> the vf_token option outside of these cases will return an error, as
> discussed above.
> Signed-off-by: Alex Williamson <>
> ---
>  drivers/vfio/pci/vfio_pci.c         |  198 +++++++++++++++++++++++++++++++++++
>  drivers/vfio/pci/vfio_pci_private.h |    8 +
>  2 files changed, 205 insertions(+), 1 deletion(-)

Reviewed-by: Cornelia Huck <>

  reply	other threads:[~2020-03-19 17:27 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-11 21:58 [PATCH v3 0/7] vfio/pci: SR-IOV support Alex Williamson
2020-03-11 21:58 ` [PATCH v3 1/7] vfio: Include optional device match in vfio_device_ops callbacks Alex Williamson
2020-03-11 21:58 ` [PATCH v3 2/7] vfio/pci: Implement match ops Alex Williamson
2020-03-11 21:58 ` [PATCH v3 3/7] vfio/pci: Introduce VF token Alex Williamson
2020-03-19 17:27   ` Cornelia Huck [this message]
2020-03-11 21:59 ` [PATCH v3 4/7] vfio: Introduce VFIO_DEVICE_FEATURE ioctl and first user Alex Williamson
2020-03-19 17:33   ` Cornelia Huck
2020-03-11 21:59 ` [PATCH v3 5/7] vfio/pci: Add sriov_configure support Alex Williamson
2020-03-19 17:44   ` Cornelia Huck
2020-03-11 21:59 ` [PATCH v3 6/7] vfio/pci: Remove dev_fmt definition Alex Williamson
2020-03-11 21:59 ` [PATCH v3 7/7] vfio/pci: Cleanup .probe() exit paths Alex Williamson
2020-03-19 17:46   ` Cornelia Huck
2020-03-19  6:32 ` [PATCH v3 0/7] vfio/pci: SR-IOV support Tian, Kevin
2020-03-19 13:11   ` Alex Williamson

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