Re: [PATCH v4 0/6] TEE subsystem for restricted dma-buf allocations

Lukas Wunner
2024-12-26T11:26:32Z

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On Thu, Dec 26, 2024 at 11:29:23AM +0530, Sumit Garg wrote:
> On Tue, 24 Dec 2024 at 14:58, Lukas Wunner <lukas@wunner.de> wrote:
> > However in the case of restricted memory, the situation is exactly
> > the opposite: The kernel may *not* be able to access the data,
> > but the crypto accelerator can access it just fine.
> >
> > I did raise a concern about this to the maintainer, but to no avail:
> > https://lore.kernel.org/r/Z1Kym1-9ka8kGHrM(a)wunner.de/
>
> Herbert's point is valid that there isn't any point for mapping
> restricted memory in the kernel virtual address space as any kernel
> access to that space can lead to platform specific hardware error
> scenarios. And for that reason we simply disallow dma_buf_mmap() and
> don't support dma_buf_vmap() for DMA-bufs holding TEE restricted
> memory.

The API for signature generation/verification (e.g. crypto_sig_sign(),
crypto_sig_verify()) no longer accepts scatterlists, only buffers in
virtual address space:

https://lore.kernel.org/all/ZIrnPcPj9Zbq51jK(a)gondor.apana.org.au/

Hence in order to use buffers in restricted memory for signature
generation/verification, you'd need to map them into virtual address
space first.

Thanks,

Lukas