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<div class="moz-cite-prefix">Am 22.07.20 um 02:22 schrieb Gurchetan
Singh:<br>
</div>
<blockquote type="cite" cite="mid:CAAfnVB=9o=xy13Z1ErgXVhcBf24TLQMGJHnfDKoSMSw2MZdg2A@mail.gmail.com">
<div dir="ltr">+Christian who added DMABUF_MOVE_NOTIFY which added
the relevant blurb:<br>
<br>
<a href="https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Ftorvalds%2Flinux.git%2Ftree%2Fdrivers%2Fdma-buf%2FKconfig%23n46&data=02%7C01%7Cchristian.koenig%40amd.com%7C5a933ce308c94d852d9708d82dd55ba6%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637309742143442589&sdata=ynsmCVRnd28gmcvQwd8PMAH3838RzbREu0ZfWUdpPpU%3D&reserved=0" originalsrc="https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/dma-buf/Kconfig#n46" shash="yyaoe2hSEpCmz9gS2ABf68G75NegfDtXQm3ItoR77iWnl+h6sCCgSSEIGOCBjWjVf1bkpl3AKQ0QPsuk6oUAceH0wPQHlMvOTW1cwcqxeCM0lEMf/jaCXJnobjOdnvoUaKNNqT5gJkLxekf8X6iJf2vdFXXVFCGLwRsmLtVCDuU=" target="_blank" moz-do-not-send="true">https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/dma-buf/Kconfig#n46</a><br>
<br>
Currently, the user seems to amdgpu for P2P dma-buf and it seems
to plumb ttm (*move_notify) callback to dma-buf. We're not sure
if it's a security issue occurring across DRM drivers, or one
more specific to the new amdgpu use case.<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, Jul 21, 2020 at 1:03
PM Chia-I Wu <<a href="mailto:olvaffe@gmail.com" target="_blank" moz-do-not-send="true">olvaffe@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi
list,<br>
<br>
virtio-gpu is moving in the direction where BO pages are
pinned for<br>
the lifetime for simplicity. I am wondering if that is
considered a<br>
security issue in general, especially after running into the<br>
description of the new DMABUF_MOVE_NOTIFY config option.<br>
</blockquote>
</div>
</blockquote>
<br>
Yes, that is generally considered a deny of service possibility and
so far Dave and Daniel have rejected all tries to upstream stuff
like this as far as I know.<br>
<br>
DMA-buf an pinning for scanout are the only exceptions since the
implementation wouldn't have been possible otherwise.<br>
<br>
<blockquote type="cite" cite="mid:CAAfnVB=9o=xy13Z1ErgXVhcBf24TLQMGJHnfDKoSMSw2MZdg2A@mail.gmail.com">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
Most drivers do not have a shrinker, or whether a BO is
purgeable is<br>
entirely controlled by the userspace (madvice). They can be<br>
categorized as "a security problem where userspace is able to
pin<br>
unrestricted amounts of memory". But those drivers are
normally found<br>
on systems without swap. I don't think the issue applies.<br>
</blockquote>
</div>
</blockquote>
<br>
This is completely independent of the availability of swap or not.<br>
<br>
Pinning of pages in large quantities can result in all kind of
problems and needs to be prevented even without swap.<br>
<br>
Otherwise you can ran into problems even with simple I/O operations
for example.<br>
<br>
<blockquote type="cite" cite="mid:CAAfnVB=9o=xy13Z1ErgXVhcBf24TLQMGJHnfDKoSMSw2MZdg2A@mail.gmail.com">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
Of the desktop GPU drivers, i915's shrinker certainly supports
purging<br>
to swap. TTM is a bit hard to follow. I can't really tell if
amdgpu<br>
or nouveau supports that. virtio-gpu is more commonly found
on<br>
systems with swaps so I think it should follow the desktop
practices?<br>
</blockquote>
</div>
</blockquote>
<br>
What we do at least in the amdgpu, radeon, i915 and nouveau is to
only allow it for scanout and that in turn is limited by the
physical number of CRTCs on the board.<br>
<br>
<blockquote type="cite" cite="mid:CAAfnVB=9o=xy13Z1ErgXVhcBf24TLQMGJHnfDKoSMSw2MZdg2A@mail.gmail.com">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
Truth is, the emulated virtio-gpu device always supports page
moves<br>
with VIRTIO_GPU_CMD_RESOURCE_{ATTACH,DETACH}_BACKING. It is
just that<br>
the driver does not make use of them. That makes this less of
an<br>
issue because the driver can be fixed anytime (finger crossed
that the<br>
emulator won't have bugs in these untested paths). This issue
becomes<br>
more urgent because we are considering adding a new HW
command[1]<br>
where page moves will be disallowed. We definitely don't want
a HW<br>
command that is inherently insecure, if BO pages pinned for
the<br>
lifetime is considered a security issue on desktops.<br>
</blockquote>
</div>
</blockquote>
<br>
Yeah, that's probably not such a good idea :)<br>
<br>
Regards,<br>
Christian.<br>
<br>
<blockquote type="cite" cite="mid:CAAfnVB=9o=xy13Z1ErgXVhcBf24TLQMGJHnfDKoSMSw2MZdg2A@mail.gmail.com">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
[1] VIRTIO_GPU_CMD_RESOURCE_CREATE_BLOB<br>
<a href="https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fvirgl%2Fdrm-misc-next%2F-%2Fblob%2Fvirtio-gpu-next%2Finclude%2Fuapi%2Flinux%2Fvirtio_gpu.h%23L396&data=02%7C01%7Cchristian.koenig%40amd.com%7C5a933ce308c94d852d9708d82dd55ba6%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637309742143452581&sdata=u90WUaJnVMDpc3SzFGHVt9Fjh5laqTr%2BxlFXbLYjp6s%3D&reserved=0" originalsrc="https://gitlab.freedesktop.org/virgl/drm-misc-next/-/blob/virtio-gpu-next/include/uapi/linux/virtio_gpu.h#L396" shash="ulg+yfZNfs/CnDBw+4UbI7ZmvExEa9IOR/hAuciCSBshHcDSj5J9plFAwahuQsLXy+TC9/d3rFFC+iiGAImJLe+trO+Og2B7ldlHV6zvFP0KfQQelCqWKWI/PE9eMpP9j83dVHRUKAsD1IIwWyB57/6rZJVClkOeVbTm7PVXWpw=" rel="noreferrer" target="_blank" moz-do-not-send="true">https://gitlab.freedesktop.org/virgl/drm-misc-next/-/blob/virtio-gpu-next/include/uapi/linux/virtio_gpu.h#L396</a><br>
</blockquote>
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</blockquote>
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