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

[Thomas Gleixner <tglx@linutronix.de>]

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