On Tue, Sep 13, 2011 at 9:03 PM, Inki Dae inki.dae@samsung.com wrote:
Hi Thomas.
-----Original Message----- From: Thomas Hellstrom [mailto:thomas@shipmail.org] Sent: Monday, September 12, 2011 3:32 PM To: Rob Clark Cc: Inki Dae; kyungmin.park@samsung.com; sw0312.kim@samsung.com; linux- arm-kernel@lists.infradead.org; dri-devel@lists.freedesktop.org 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 Hellstromthomas@shipmail.org 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/%3E v2:< http://www.spinics.net/lists/kernel/msg1224275.html%3E v3:< http://www.gossamer-threads.com/lists/linux/kernel/1423684%3E
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 Daeinki.dae@samsung.com Signed-off-by: Joonyoung Shimjy0922.shim@samsung.com Signed-off-by: SeungWoo Kimsw0312.kim@samsung.com Signed-off-by: kyungmin.parkkyungmin.park@samsung.com
+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)..
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