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Date:   Wed, 16 Jun 2021 13:08:38 +0100
From:   Will Deacon <will@kernel.org>
To:     Claire Chang <tientzu@chromium.org>
Cc:     Rob Herring <robh+dt@kernel.org>, mpe@ellerman.id.au,
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Subject: Re: [PATCH v12 00/12] Restricted DMA
Message-ID: <20210616120837.GA22783@willie-the-truck>
References: <20210616062157.953777-1-tientzu@chromium.org>
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Hi Claire,

On Wed, Jun 16, 2021 at 02:21:45PM +0800, Claire Chang wrote:
> This series implements mitigations for lack of DMA access control on
> systems without an IOMMU, which could result in the DMA accessing the
> system memory at unexpected times and/or unexpected addresses, possibly
> leading to data leakage or corruption.
> 
> For example, we plan to use the PCI-e bus for Wi-Fi and that PCI-e bus is
> not behind an IOMMU. As PCI-e, by design, gives the device full access to
> system memory, a vulnerability in the Wi-Fi firmware could easily escalate
> to a full system exploit (remote wifi exploits: [1a], [1b] that shows a
> full chain of exploits; [2], [3]).
> 
> To mitigate the security concerns, we introduce restricted DMA. Restricted
> DMA utilizes the existing swiotlb to bounce streaming DMA in and out of a
> specially allocated region and does memory allocation from the same region.
> The feature on its own provides a basic level of protection against the DMA
> overwriting buffer contents at unexpected times. However, to protect
> against general data leakage and system memory corruption, the system needs
> to provide a way to restrict the DMA to a predefined memory region (this is
> usually done at firmware level, e.g. MPU in ATF on some ARM platforms [4]).
> 
> [1a] https://googleprojectzero.blogspot.com/2017/04/over-air-exploiting-broadcoms-wi-fi_4.html
> [1b] https://googleprojectzero.blogspot.com/2017/04/over-air-exploiting-broadcoms-wi-fi_11.html
> [2] https://blade.tencent.com/en/advisories/qualpwn/
> [3] https://www.bleepingcomputer.com/news/security/vulnerabilities-found-in-highly-popular-firmware-for-wifi-chips/
> [4] https://github.com/ARM-software/arm-trusted-firmware/blob/master/plat/mediatek/mt8183/drivers/emi_mpu/emi_mpu.c#L132
> 
> v12:
> Split is_dev_swiotlb_force into is_swiotlb_force_bounce (patch 06/12) and
> is_swiotlb_for_alloc (patch 09/12)

I took this for a spin in an arm64 KVM guest with virtio devices using the
DMA API and it works as expected on top of swiotlb devel/for-linus-5.14, so:

Tested-by: Will Deacon <will@kernel.org>

Thanks!

Will