linux-kernel - Re: [PATCH v6 02/14] Documentation/x86: Secure Launch kernel documentation

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Date:   Fri, 12 May 2023 15:19:46 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ross Philipson <ross.philipson@...cle.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-integrity@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-crypto@...r.kernel.org, iommu@...ts.linux-foundation.org,
        kexec@...ts.infradead.org, linux-efi@...r.kernel.org
Cc:     ross.philipson@...cle.com, dpsmith@...rtussolutions.com,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, ardb@...nel.org,
        mjg59@...f.ucam.org, James.Bottomley@...senpartnership.com,
        luto@...capital.net, nivedita@...m.mit.edu,
        kanth.ghatraju@...cle.com, trenchboot-devel@...glegroups.com
Subject: Re: [PATCH v6 02/14] Documentation/x86: Secure Launch kernel
 documentation

On Thu, May 04 2023 at 14:50, Ross Philipson wrote:
> +KASLR Configuration
> +-------------------
> +
> +Secure Launch does not interoperate with KASLR. If possible, the MLE should be
> +built with KASLR disabled::

Why?

> +  "Processor type and features" -->
> +      "Build a relocatable kernel" -->
> +          "Randomize the address of the kernel image (KASLR) [ ]"
> +
> +This unsets the Kconfig value CONFIG_RANDOMIZE_BASE.
> +
> +If not possible, KASLR must be disabled on the kernel command line when doing
> +a Secure Launch as follows::
> +
> +  nokaslr

So what happens if KASLR is enabled in Kconfig and not disabled on the
command line?

> +IOMMU Configuration
> +-------------------
> +
> +When doing a Secure Launch, the IOMMU should always be enabled and the drivers
> +loaded. However, IOMMU passthrough mode should never be used. This leaves the
> +MLE completely exposed to DMA after the PMR's [2]_ are disabled. The current default
> +mode is to use IOMMU in lazy translated mode but strict translated mode is the preferred
> +IOMMU mode and this should be selected in the build configuration::
> +
> +  "Device Drivers" -->
> +      "IOMMU Hardware Support" -->
> +          "IOMMU default domain type" -->
> +              "(X) Translated - Strict"
> +
> +In addition, the Intel IOMMU should be on by default. The following sets this as the
> +default in the build configuration::
> +
> +  "Device Drivers" -->
> +      "IOMMU Hardware Support" -->
> +          "Support for Intel IOMMU using DMA Remapping Devices [*]"
> +
> +and::
> +
> +  "Device Drivers" -->
> +      "IOMMU Hardware Support" -->
> +          "Support for Intel IOMMU using DMA Remapping Devices [*]" -->
> +              "Enable Intel DMA Remapping Devices by default  [*]"
> +
> +It is recommended that no other command line options should be set to override
> +the defaults above.

Is any of this validated and are proper warnings emitted or is it just
recommended and left to the user to do the right thing?

Thanks,

        tglx