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
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
On Thu, Sep 16, 2021 at 02:31:34PM +0200, Daniel Vetter 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?
It is a combination of uAPI and HW specification.
revoke here means you take a MR object and tell it to stop doing DMA without causing the MR object to be destructed.
All the drivers can of course destruct the MR, but doing such a destruction without explicit synchronization with user space opens things up to a serious use-after potential that could be a security issue.
When the open handle closes the userspace is synchronized with the kernel and we can destruct the HW objects safely.
So, the special HW feature required is 'stop doing DMA but keep the object in an error state' which isn't really implemented, and doesn't extend very well to other object types beyond simple MRs.
User A opens gaudi device, sets up dma-buf export
User A registers that with RDMA, or anything else that doesn't support
revoke.
User A closes gaudi device
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
I would expect this is blocked so long as the DMABUF exists - eg the DMABUF will hold a fget on the FD of #1 until the DMABUF is closed, so that #3 can't actually happen.
It's not mlocked memory, it's mlocked memory and I can exfiltrate it.
That's just bug, don't make buggy drivers :)
Jason
On Thu, Sep 16, 2021 at 10:10:14AM -0300, Jason Gunthorpe wrote:
On Thu, Sep 16, 2021 at 02:31:34PM +0200, Daniel Vetter 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?
It is a combination of uAPI and HW specification.
revoke here means you take a MR object and tell it to stop doing DMA without causing the MR object to be destructed.
All the drivers can of course destruct the MR, but doing such a destruction without explicit synchronization with user space opens things up to a serious use-after potential that could be a security issue.
When the open handle closes the userspace is synchronized with the kernel and we can destruct the HW objects safely.
So, the special HW feature required is 'stop doing DMA but keep the object in an error state' which isn't really implemented, and doesn't extend very well to other object types beyond simple MRs.
Yeah revoke without destroying the MR doesn't work, and it sounds like revoke by destroying the MR just moves the can of worms around to another place.
User A opens gaudi device, sets up dma-buf export
User A registers that with RDMA, or anything else that doesn't support
revoke.
User A closes gaudi device
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
I would expect this is blocked so long as the DMABUF exists - eg the DMABUF will hold a fget on the FD of #1 until the DMABUF is closed, so that #3 can't actually happen.
It's not mlocked memory, it's mlocked memory and I can exfiltrate it.
That's just bug, don't make buggy drivers :)
Well yeah, but given that habanalabs hand rolled this I can't just check for the usual things we have to enforce this in drm. And generally you can just open chardevs arbitrarily, and multiple users fighting over each another. The troubles only start when you have private state or memory allocations of some kind attached to the struct file (instead of the underlying device), or something else that requires device exclusivity. There's no standard way to do that.
Plus in many cases you really want revoke on top (can't get that here unfortunately it seems), and the attempts to get towards a generic revoke() just never went anywhere. So again it's all hand-rolled per-subsystem. *insert lament about us not having done this through a proper subsystem*
Anyway it sounds like the code takes care of that. -Daniel
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