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    SubjectRe: [PATCH RFC] tpm: define a command filter
    On Tue, Jan 24, 2017 at 12:07:07PM -0700, Jason Gunthorpe wrote:
    > On Tue, Jan 24, 2017 at 04:36:00PM +0200, Jarkko Sakkinen wrote:
    > > On Mon, Jan 23, 2017 at 05:19:18PM -0700, Jason Gunthorpe wrote:
    > > > On Tue, Jan 24, 2017 at 02:02:52AM +0200, Jarkko Sakkinen wrote:
    > > > > This commit adds a command filter for whitelisting a set of commands in
    > > > > a TPM space. When a TPM space is created through /dev/tpms0, no
    > > > > commands are allowed. The user of the TPM space must explicitly define
    > > > > the list of commands allowed before sending any commands. This ioctl is
    > > > > a one shot call so that a resource manager daemon can call it before
    > > > > sending the file descriptor to the client.
    > > >
    > > > I don't think it makes sense to have a daemon in user space that
    > > > passes an open'd /dev/tpms0 FD directly to a client..
    > > >
    > > > It is trivial and more powerful to just proxy the messages. Can you
    > > > see some reason why passing a FD through a daemon would make sense?
    > > >
    > > > The earlier discussion with James was to have some way to apply a
    > > > global command filter to all tpms0 users with the idea that the
    > > > 'right' restricted command set would enable a 0666 cdev node, and no
    > > > daemon.
    > >
    > > Is that a conflicting goal?
    > >
    > > Maybe the ioctl could be restricted by CAP_MAC_ADMIN in that case?
    >
    > I think you need to spell out a clear use case for how userspace
    > should use this filter feature and why having the kernel involved is a
    > necessary element.
    >
    > Driving userspace from the kernel uAPI design is a bit tricky without
    > participation from people writing the user space code.
    >
    > > How would you propose to change the code below? I guess the "core
    > > code" is about right and this is more about API, am I right?
    >
    > Generally, I'm of the opinion it is better to introduce the minimal
    > amount of uAPI at this point and wait until people working on
    > userspace figure out basic questions like, will there be a TPM2 daemon
    > or not..
    >
    > I would focus now on getting the RFC series finished up, hook the
    > kAPI users into spaces and get it to the point where it does let
    > user & kernel safely share the TPM.
    >
    > Jason

    There should be anyway someway to limit what commands can be sent but
    I understand your point.

    Would it make more sense to have a sysfs file for configuring the
    global filter that would get the data in the same format (list of
    16-bit words)?

    /Jarkko

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