Am 26.06.24 um 10:05 schrieb Jason-JH Lin (林睿祥):
In the step 3), we need to verify the dma-buf is allocated from "restricted_mtk_cma", but there is no way to pass the secure flag or private data from userspace to the import interface in DRM driver.
Why do you need to verify that?
I need to know the imported buffer is allocated from restricted cma and mark it as a secure buffer in mediatek-drm driver. Then, I will add some configuration to the hardware if the buffer is secure buffer, so that it can get the permission to access the secure buffer.
Yeah so far that makes sense. This is basically what other drivers do with secure buffers as well.
But why do you want the kernel to transport that information? Usually drivers get the information from userspace what to do with a buffer.
In other words the format, stride, tilling and also if it's a secure buffer or not comes from userspace.
What the hardware usually handles internally is things like encryption keys, but you eventually get the information where to look for the key from userspace as well.
Handling inside the kernel would only be necessary if userspace could for example crash the system with invalid parameters. But for encryption that is usually not the case.
So I can only verify it like this now: struct drm_gem_object *mtk_gem_prime_import_sg_table(struct drm_device *dev, struct dma_buf_attachment *attach, struct sg_table *sg) { struct mtk_gem_obj *mtk_gem;
/* check if the entries in the sg_table are contiguous */ if (drm_prime_get_contiguous_size(sg) < attach->dmabuf->size) { DRM_ERROR("sg_table is not contiguous"); return ERR_PTR(-EINVAL); } mtk_gem = mtk_gem_init(dev, attach->dmabuf->size); if (IS_ERR(mtk_gem)) return ERR_CAST(mtk_gem);
- mtk_gem->secure = (!strncmp(attach->dmabuf->exp_name,
"restricted", 10)); mtk_gem->dma_addr = sg_dma_address(sg->sgl); mtk_gem->size = attach->dmabuf->size; mtk_gem->sg = sg;
return &mtk_gem->base;}
Complete NAK from my side to that approach. Importing of a DMA-buf should be independent of the exporter.
What you could do is to provide the secure buffer from a device and not a device heap.
You mean I should allocate buffer in mediate-drm driver not userspace?
Well that depends. The question is if you have multiple drivers which needs to work with this secure buffer?
If yes then you should have a general allocation heap for it. If no then the buffers could as well be allocated from the driver interface directly.
I just have modified this to userspace by the comment here:
https://patchwork.kernel.org/project/linux-mediatek/patch/20240403102701.369...
I think I have the same problem as the ECC_FLAG mention in:
https://lore.kernel.org/linux-media/20240515-dma-buf-ecc-heap-v1-0-54cbbd049...
I think it would be better to have the user configurable private information in dma-buf, so all the drivers who have the same requirement can get their private information from dma-buf directly and no need to change or add the interface.
What's your opinion in this point?
Well of hand I don't see the need for that.
What happens if you get a non-secure buffer imported in your secure device?
We use the same mediatek-drm driver for secure and non-secure buffer. If non-secure buffer imported to mediatek-drm driver, it's go to the normal flow with normal hardware settings.
We use different configurations to make hardware have different permission to access the buffer it should access.
So if we can't get the information of "the buffer is allocated from restricted_mtk_cma" when importing the buffer into the driver, we won't be able to configure the hardware correctly.
Why can't you get this information from userspace?
Regards, Christian.
Regards, Jason-JH.Lin
Regards, Christian.
Regards, Jason-JH.Lin
Regards, Christian.
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On Wed, Jun 26, 2024 at 12:49:02PM +0200, Christian König wrote:
Am 26.06.24 um 10:05 schrieb Jason-JH Lin (林睿祥):
I think I have the same problem as the ECC_FLAG mention in:
https://lore.kernel.org/linux-media/20240515-dma-buf-ecc-heap-v1-0-54cbbd049... I think it would be better to have the user configurable private
information in dma-buf, so all the drivers who have the same requirement can get their private information from dma-buf directly and no need to change or add the interface.
What's your opinion in this point?
Well of hand I don't see the need for that. What happens if you get a non-secure buffer imported in your secure
device?
We use the same mediatek-drm driver for secure and non-secure buffer. If non-secure buffer imported to mediatek-drm driver, it's go to the normal flow with normal hardware settings.
We use different configurations to make hardware have different permission to access the buffer it should access.
So if we can't get the information of "the buffer is allocated from restricted_mtk_cma" when importing the buffer into the driver, we won't be able to configure the hardware correctly.
Why can't you get this information from userspace?
Same reason amd and i915/xe also pass this around internally in the kernel, it's just that for those gpus the render and kms node are the same driver so this is easy.
But on arm you have split designs everywhere and dma-buf import/export, so something else is needed. And neither current kms uapi nor protocols/extensions have provisions for this (afaik) because it works on the big gpus, and on android it's just hacked up with backchannels.
So yeah essentially I think we probably need something like this, as much as it sucks. I see it somewhat similar to handling pcip2pdma limitations in the kernel too.
Not sure where/how it should be handled though, and maybe I've missed something around protocols, in which case I guess we should add some secure buffer flags to the ADDFB2 ioctl. -Sima
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