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c51e97e7f1
Even though our EFI zboot decompressor is pedantically spec compliant and idiomatic for EFI image loaders, calling LoadImage() and StartImage() for the nested image is a bit of a burden. Not only does it create workflow issues for the distros (as both the inner and outer PE/COFF images need to be signed for secure boot), it also copies the image around in memory numerous times: - first, the image is decompressed into a buffer; - the buffer is consumed by LoadImage(), which copies the sections into a newly allocated memory region to hold the executable image; - once the EFI stub is invoked by StartImage(), it will also move the image in memory in case of KASLR, mirrored memory or if the image must execute from a certain a priori defined address. There are only two EFI spec compliant ways to load code into memory and execute it: - use LoadImage() and StartImage(), - call ExitBootServices() and take ownership of the entire system, after which anything goes. Given that the EFI zboot decompressor always invokes the EFI stub, and given that both are built from the same set of objects, let's merge the two, so that we can avoid LoadImage()/StartImage but still load our image into memory without breaking the above rules. This also means we can decompress the image directly into its final location, which could be randomized or meet other platform specific constraints that LoadImage() does not know how to adhere to. It also means that, even if the encapsulated image still has the EFI stub incorporated as well, it does not need to be signed for secure boot when wrapping it in the EFI zboot decompressor. In the future, we might decide to retire the EFI stub attached to the decompressed image, but for the time being, they can happily coexist. Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.