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
next prev 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 [PATCH v6 0/2] Add p2p via dmabuf to habanalabs 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YUSJL9ml1MljOwzB@phenom.ffwll.local \
--to=daniel@ffwll.ch \
--cc=airlied@gmail.com \
--cc=alexander.deucher@amd.com \
--cc=amd-gfx@lists.freedesktop.org \
--cc=christian.koenig@amd.com \
--cc=dledford@redhat.com \
--cc=dri-devel@lists.freedesktop.org \
--cc=galpress@amazon.com \
--cc=gregkh@linuxfoundation.org \
--cc=hch@lst.de \
--cc=jgg@ziepe.ca \
--cc=leonro@nvidia.com \
--cc=linaro-mm-sig@lists.linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-media@vger.kernel.org \
--cc=linux-rdma@vger.kernel.org \
--cc=ogabbay@kernel.org \
--cc=sleybo@amazon.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).