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From: Daniel Vetter <daniel@ffwll.ch>
To: Oded Gabbay <ogabbay@kernel.org>
Cc: "Jason Gunthorpe" <jgg@ziepe.ca>,
	"Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Christian König" <christian.koenig@amd.com>,
	"Gal Pressman" <galpress@amazon.com>,
	"Yossi Leybovich" <sleybo@amazon.com>,
	"Maling list - DRI developers" <dri-devel@lists.freedesktop.org>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	"Linux Media Mailing List" <linux-media@vger.kernel.org>,
	"Doug Ledford" <dledford@redhat.com>,
	"Dave Airlie" <airlied@gmail.com>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Leon Romanovsky" <leonro@nvidia.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
	"moderated list:DMA BUFFER SHARING FRAMEWORK"
	<linaro-mm-sig@lists.linaro.org>
Subject: Re: [PATCH v6 0/2] Add p2p via dmabuf to habanalabs
Date: Fri, 17 Sep 2021 14:25:19 +0200	[thread overview]
Message-ID: <YUSJL9ml1MljOwzB@phenom.ffwll.local> (raw)
In-Reply-To: <CAFCwf10MnK5KPBaeWar4tALGz9n8+-B8toXnqurcebZ8Y_Jjpw@mail.gmail.com>

On Thu, Sep 16, 2021 at 03:44:25PM +0300, Oded Gabbay wrote:
> On Thu, Sep 16, 2021 at 3:31 PM Daniel Vetter <daniel@ffwll.ch> wrote:
> >
> > On Wed, Sep 15, 2021 at 10:45:36AM +0300, Oded Gabbay wrote:
> > > On Tue, Sep 14, 2021 at 7:12 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > > >
> > > > On Tue, Sep 14, 2021 at 04:18:31PM +0200, Daniel Vetter wrote:
> > > > > On Sun, Sep 12, 2021 at 07:53:07PM +0300, Oded Gabbay wrote:
> > > > > > Hi,
> > > > > > Re-sending this patch-set following the release of our user-space TPC
> > > > > > compiler and runtime library.
> > > > > >
> > > > > > I would appreciate a review on this.
> > > > >
> > > > > I think the big open we have is the entire revoke discussions. Having the
> > > > > option to let dma-buf hang around which map to random local memory ranges,
> > > > > without clear ownership link and a way to kill it sounds bad to me.
> > > > >
> > > > > I think there's a few options:
> > > > > - We require revoke support. But I've heard rdma really doesn't like that,
> > > > >   I guess because taking out an MR while holding the dma_resv_lock would
> > > > >   be an inversion, so can't be done. Jason, can you recap what exactly the
> > > > >   hold-up was again that makes this a no-go?
> > > >
> > > > RDMA HW can't do revoke.
> >
> > Like why? I'm assuming when the final open handle or whatever for that MR
> > is closed, you do clean up everything? Or does that MR still stick around
> > forever too?
> >
> > > > So we have to exclude almost all the HW and several interesting use
> > > > cases to enable a revoke operation.
> > > >
> > > > >   - For non-revokable things like these dma-buf we'd keep a drm_master
> > > > >     reference around. This would prevent the next open to acquire
> > > > >     ownership rights, which at least prevents all the nasty potential
> > > > >     problems.
> > > >
> > > > This is what I generally would expect, the DMABUF FD and its DMA
> > > > memory just floats about until the unrevokable user releases it, which
> > > > happens when the FD that is driving the import eventually gets closed.
> > > This is exactly what we are doing in the driver. We make sure
> > > everything is valid until the unrevokable user releases it and that
> > > happens only when the dmabuf fd gets closed.
> > > And the user can't close it's fd of the device until he performs the
> > > above, so there is no leakage between users.
> >
> > Maybe I got the device security model all wrong, but I thought Guadi is
> > single user, and the only thing it protects is the system against the
> > Gaudi device trhough iommu/device gart. So roughly the following can
> > happen:
> >
> > 1. User A opens gaudi device, sets up dma-buf export
> >
> > 2. User A registers that with RDMA, or anything else that doesn't support
> > revoke.
> >
> > 3. User A closes gaudi device
> This can not happen without User A closing the FD of the dma-buf it exported.
> We prevent User A from closing the device because when it exported the
> dma-buf, the driver's code took a refcnt of the user's private
> structure. You can see that in export_dmabuf_common() in the 2nd
> patch. There is a call there to hl_ctx_get.
> So even if User A calls close(device_fd), the driver won't let any
> other user open the device until User A closes the fd of the dma-buf
> object.
> 
> Moreover, once User A will close the dma-buf fd and the device is
> released, the driver will scrub the device memory (this is optional
> for systems who care about security).
> 
> And AFAIK, User A can't close the dma-buf fd once it registered it
> with RDMA, without doing unregister.
> This can be seen in ib_umem_dmabuf_get() which calls dma_buf_get()
> which does fget(fd)

Yeah that's essentially what I was looking for. This is defacto
hand-rolling the drm_master owner tracking stuff. As long as we have
something like this in place it should be fine I think.
-Daniel

> > 4. User B opens gaudi device, assumes that it has full control over the
> > device and uploads some secrets, which happen to end up in the dma-buf
> > region user A set up
> >
> > 5. User B extracts secrets.
> >
> > > > I still don't think any of the complexity is needed, pinnable memory
> > > > is a thing in Linux, just account for it in mlocked and that is
> > > > enough.
> >
> > It's not mlocked memory, it's mlocked memory and I can exfiltrate it.
> > Mlock is fine, exfiltration not so much. It's mlock, but a global pool and
> > if you didn't munlock then the next mlock from a completely different user
> > will alias with your stuff.
> >
> > Or is there something that prevents that? Oded at least explain that gaudi
> > works like a gpu from 20 years ago, single user, no security at all within
> > the device.
> > -Daniel
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

  parent reply	other threads:[~2021-09-17 12:25 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-12 16:53 Oded Gabbay
2021-09-12 16:53 ` [PATCH v6 1/2] habanalabs: define uAPI to export FD for DMA-BUF Oded Gabbay
2021-09-28 17:13   ` Jason Gunthorpe
2021-09-28 19:12     ` Oded Gabbay
2021-09-12 16:53 ` [PATCH v6 2/2] habanalabs: add support for dma-buf exporter Oded Gabbay
2021-09-28 17:36   ` Jason Gunthorpe
2021-09-28 21:17     ` Oded Gabbay
2021-09-30 12:46       ` Oded Gabbay
2021-10-01 14:52         ` Jason Gunthorpe
2021-10-01 14:50       ` Jason Gunthorpe
2021-09-14 14:18 ` [PATCH v6 0/2] Add p2p via dmabuf to habanalabs Daniel Vetter
2021-09-14 14:58   ` Oded Gabbay
2021-09-14 16:12   ` Jason Gunthorpe
2021-09-15  7:45     ` Oded Gabbay
2021-09-16 12:31       ` Daniel Vetter
2021-09-16 12:44         ` Oded Gabbay
2021-09-16 13:16           ` Oded Gabbay
2021-09-17 12:25           ` Daniel Vetter [this message]
2021-09-16 13:10         ` Jason Gunthorpe
2021-09-17 12:30           ` Daniel Vetter
2021-09-18  8:38             ` Oded Gabbay
2021-09-23  9:22               ` Oded Gabbay
2021-09-28  7:04                 ` Oded Gabbay
2021-09-30  9:13                   ` Daniel Vetter

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