On 09/14/2011 07:55 AM, Inki Dae wrote:
-----Original Message-----
From: Rob Clark [mailto:robdclark@xxxxxxxxx]
Sent: Wednesday, September 14, 2011 11:26 AM
To: Inki Dae
Cc: Thomas Hellstrom; kyungmin.park@xxxxxxxxxxx; sw0312.kim@xxxxxxxxxxx;
linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx
Subject: Re: [PATCH v4] DRM: add DRM Driver for Samsung SoC EXYNOS4210.
On Tue, Sep 13, 2011 at 9:03 PM, Inki Dae<inki.dae@xxxxxxxxxxx> wrote:
Hi Thomas.
-----Original Message-----
From: Thomas Hellstrom [mailto:thomas@xxxxxxxxxxxx]
Sent: Monday, September 12, 2011 3:32 PM
To: Rob Clark
Cc: Inki Dae; kyungmin.park@xxxxxxxxxxx; sw0312.kim@xxxxxxxxxxx; linux-
arm-kernel@xxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx
Subject: Re: [PATCH v4] DRM: add DRM Driver for Samsung SoC EXYNOS4210.
On 09/11/2011 11:26 PM, Thomas Hellstrom wrote:
On 09/10/2011 07:31 PM, Rob Clark wrote:
On Sat, Sep 10, 2011 at 9:04 AM, Thomas
Hellstrom<thomas@xxxxxxxxxxxx> wrote:
On 09/09/2011 01:38 PM, Inki Dae wrote:
This patch is a DRM Driver for Samsung SoC Exynos4210 and now
enables
only FIMD yet but we will add HDMI support also in the future.
from now on, I will remove RFC prefix because I think we have got
comments
enough.
this patch is based on git repository below:
git://git.kernel.org/pub/scm/linux/kernel/git/airlied/drm-2.6.git,
branch name: drm-next
commit-id: bcc65fd8e929a9d9d34d814d6efc1d2793546922
you can refer to our working repository below:
http://git.infradead.org/users/kmpark/linux-2.6-samsung
branch name: samsung-drm
We tried to re-use lowlevel codes of the FIMD driver(s3c-fb.c
based on Linux framebuffer) but couldn't so because lowlevel codes
of s3c-fb.c are included internally and so FIMD module of this
driver has
its own lowlevel codes.
We used GEM framework for buffer management and DMA
APIs(dma_alloc_*)
for buffer allocation. by using DMA API, we could use CMA later.
Refer to this link for CMA(Continuous Memory Allocator):
http://lkml.org/lkml/2011/7/20/45
this driver supports only physically continuous memory(non-iommu).
Links to previous versions of the patchset:
v1:< https://lwn.net/Articles/454380/>
v2:< http://www.spinics.net/lists/kernel/msg1224275.html>
v3:< http://www.gossamer-
threads.com/lists/linux/kernel/1423684>
Changelog v2:
DRM: add DRM_IOCTL_SAMSUNG_GEM_MMAP ioctl command.
this feature maps user address space to physical memory
region
once user application requests DRM_IOCTL_SAMSUNG_GEM_MMAP
ioctl.
DRM: code clean and add exception codes.
Changelog v3:
DRM: Support multiple irq.
FIMD and HDMI have their own irq handler but DRM Framework
can
regiter
only one irq handler this patch supports mutiple irq for
Samsung SoC.
DRM: Consider modularization.
each DRM, FIMD could be built as a module.
DRM: Have indenpendent crtc object.
crtc isn't specific to SoC Platform so this patch gets a crtc
to be used as common object.
created crtc could be attached to any encoder object.
DRM: code clean and add exception codes.
Changelog v4:
DRM: remove is_defult from samsung_fb.
is_default isn't used for default framebuffer.
DRM: code refactoring to fimd module.
this patch is be considered with multiple display objects and
would use its own request_irq() to register a irq handler
instead of
drm framework's one.
DRM: remove find_samsung_drm_gem_object()
DRM: move kernel private data structures and definitions to driver
folder.
samsung_drm.h would contain only public information for
userspace
ioctl interface.
DRM: code refactoring to gem modules.
buffer module isn't dependent of gem module anymore.
DRM: fixed security issue.
DRM: remove encoder porinter from specific connector.
samsung connector doesn't need to have generic encoder.
DRM: code clean and add exception codes.
Signed-off-by: Inki Dae<inki.dae@xxxxxxxxxxx>
Signed-off-by: Joonyoung Shim<jy0922.shim@xxxxxxxxxxx>
Signed-off-by: SeungWoo Kim<sw0312.kim@xxxxxxxxxxx>
Signed-off-by: kyungmin.park<kyungmin.park@xxxxxxxxxxx>
---
+static struct drm_ioctl_desc samsung_ioctls[] = {
+ DRM_IOCTL_DEF_DRV(SAMSUNG_GEM_CREATE,
samsung_drm_gem_create_ioctl,
+ DRM_UNLOCKED | DRM_AUTH),
Hi!
With reference my previous security comment.
Let's say you have a compromised video player running as a DRM
client, that
tries to repeatedly allocate huge GEM buffers...
What will happen when all DMA memory is exhausted? Will this cause
other
device drivers to see an OOM, or only DRM?
The old DRI model basically allowed any authorized DRI client to
exhaust
video ram or AGP memory, but never system memory. Newer DRI drivers
typically only allow DRI masters to do that.
as
I don't think an authorized DRI client should be able to easily
exhaust
resources (DMA memory) used by other device drivers causing them to
fail.
I'm not entirely sure what else can be done, other than have a
threshold on max MB allocatable of buffer memory..
Yes, I think that's what needs to be done, and that threshold should
be low enough to keep other device drivers running in the worst
allocation case.
In the samsung driver case, he is only allocating scanout memory
from
CMA, so the limit will be the CMA region size.. beyond that you
can't
get physically contiguous memory. So I think this driver is safe.
It's not really what well-behaved user-space drivers do that should
be
a concern, but what compromized application *might* do that is a
concern.
Hmm. I might have missed your point here. If the buffer allocation
ioctl
only allows allocating CMA memory, then I agree the driver fits the old
DRI security model, as long as no other devices on the platform will
ever use CMA.
But in that case, there really should be a way for the driver to say
"Hey, all CMA memory on this system is mine", in the same way
traditional video drivers can claim the VRAM PCI resource.
CMA could reserve memory region for a specific driver so DRM Client
could
request memory allocation from only the region.
This is to avoid the possibility that future drivers that need CMA will
be vulnerable to DOS-attacks from ill-behaved DRI clients.
Thomas, if any application has root authority for ill-purpose then isn't
it
possible to be vulnerable to DOS-attacks? I think DRM_AUTH means root
authority. I know DRM Framework gives any root application DRM_AUTH
authority for compatibility.
DRM_AUTH just means that the client has authenticated w/ X11 (meaning
that it has permission to connect to x server)..
Yes, I understood so. but see drm_open_helper() of drm_fops.c file please.
in this function, you can see a line below.
/* for compatibility root is always authenticated */
priv->authenticated = capable(CAP_SYS_ADMIN)
I think the code above says that any application with root permission is
authenticated.
Yes, that is true. A root client may be assumed to have AUTH
permissions, but the inverse does not hold, meaning that an AUTH client
may *not* be assumed to have root permissions. I think there is a
ROOT_ONLY ioctl flag for that.
The problem I'm seeing compared to other drivers is the following:
Imagine for example that you have a disc driver that allocates temporary
memory out of the same DMA pool as the DRM driver.
Now you have a video player that is a DRM client. It contains a security
flaw and is compromized by somebody trying to play a specially crafted
video stream. The video player starts to allocate gem buffers until it
receives an -ENOMEM. Then it stops allocating and does nothing.
Now the system tries an important disc access (paging for example). This
fails, because the video player has exhausted all DMA memory and the
disc driver fails to allocate.
The system is dead.
The point is:
If there is a chance that other drivers will use the same DMA/CMA pool
as the DRM driver, DRM must leave enough DMA/CMA memory for those
drivers to work.
The difference compared to other drm drivers:
There are other drm drivers that work the same way, with a static
allocator. For example "via" and "sis". But those drivers completely
claim the resources they are using. Nobody else is expected to use VRAM
/ AGP.
In the Samsung case, it's not clear to me whether the DMA/CMA pool *can*
be shared with other devices.
If it is, IMHO you must implement an allocation limit in DRM, if not,
the driver should probably be safe.
Thanks,
Thomas
But I think that since memory allocation is limited to the size of the
CMA region, that this puts a reasonable cap of the memory that can be
allocated by the client. If this is a problem, it certainly isn't the
worst problem. You could still limit via file permissions the users
that can open the DRM device file, so it is really no worse than other
devices like v4l2..
BR,
-R
/Thomas
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