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Date: Thu, 12 Dec 2024 06:40:14 +0100
From: Christoph Hellwig <hch@lst.de>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Ahmad Fatoum <a.fatoum@pengutronix.de>, kasan-dev@googlegroups.com,
	iommu@lists.linux.dev, Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Christoph Hellwig <hch@lst.de>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Marco Elver <elver@google.com>, Kees Cook <keescook@chromium.org>,
	Pengutronix Kernel Team <kernel@pengutronix.de>
Subject: Re: Using KASAN to catch streaming DMA API violations
Message-ID: <20241212054014.GA4695@lst.de>
References: <72ad8ca7-5280-457e-9769-b8a645966105@pengutronix.de> <360e2ec9-556e-4507-a539-f86f7619fe29@app.fastmail.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Fri, Dec 06, 2024 at 09:14:27AM +0100, Arnd Bergmann wrote:
> Right. I would go even further and say that transferring ownership
> to the device poisons an area that is aligned to ARCH_DMA_MINALIGN,
> making it possibly bigger on both ends of the area. Transferring
> ownership back to the CPU only unpoisons the exact area that was
> specified, leaving the unaligned bytes around it as uninitialized.

Yes.

> That may need to be controlled by an additional Kconfig option on
> top of poisoning the data initially.

Note that we'll definitively need a config option for the basic
checks as well.  There is plenty o drivers that don't do any DMA
ownership management right now.  And while I'd like to see everything
fixed it's going to take a while to get there.