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

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Message-ID: <Z209ZegsmgN1xlNG@wunner.de>
Date: Thu, 26 Dec 2024 12:26:29 +0100
From: Lukas Wunner <lukas@...ner.de>
To: Sumit Garg <sumit.garg@...aro.org>
Cc: simona.vetter@...ll.ch, Jens Wiklander <jens.wiklander@...aro.org>,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
	op-tee@...ts.trustedfirmware.org,
	linux-arm-kernel@...ts.infradead.org,
	Olivier Masse <olivier.masse@....com>,
	Thierry Reding <thierry.reding@...il.com>,
	Yong Wu <yong.wu@...iatek.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Benjamin Gaignard <benjamin.gaignard@...labora.com>,
	Brian Starkey <Brian.Starkey@....com>,
	John Stultz <jstultz@...gle.com>,
	"T . J . Mercier" <tjmercier@...gle.com>,
	Christian König <christian.koenig@....com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	azarrabi@....qualcomm.com
Subject: Re: [PATCH v4 0/6] TEE subsystem for restricted dma-buf allocations

On Thu, Dec 26, 2024 at 11:29:23AM +0530, Sumit Garg wrote:
> On Tue, 24 Dec 2024 at 14:58, Lukas Wunner <lukas@...ner.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@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@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