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Date: Mon, 2 Dec 2019 16:42:57 -0800 From: Matthew Garrett <mjg59@...gle.com> To: linux-efi <linux-efi@...r.kernel.org> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>, x86@...nel.org, linux-pci@...r.kernel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] [EFI,PCI] Allow disabling PCI busmastering on bridges during boot On Mon, Dec 2, 2019 at 4:40 PM Matthew Garrett <matthewgarrett@...gle.com> wrote: > > Add an option to disable the busmaster bit in the control register on > all PCI bridges before calling ExitBootServices() and passing control to > the runtime kernel. System firmware may configure the IOMMU to prevent > malicious PCI devices from being able to attack the OS via DMA. However, > since firmware can't guarantee that the OS is IOMMU-aware, it will tear > down IOMMU configuration when ExitBootServices() is called. This leaves > a window between where a hostile device could still cause damage before > Linux configures the IOMMU again. I don't know enough about ARM to know if this makes sense there as well. Anyone?
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