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9c55461040
Currently, the EFI stub invokes the EFI memory attributes protocol to strip any NX restrictions from the entire loaded kernel, resulting in all code and data being mapped read-write-execute. The point of the EFI memory attributes protocol is to remove the need for all memory allocations to be mapped with both write and execute permissions by default, and make it the OS loader's responsibility to transition data mappings to code mappings where appropriate. Even though the UEFI specification does not appear to leave room for denying memory attribute changes based on security policy, let's be cautious and avoid relying on the ability to create read-write-execute mappings. This is trivially achievable, given that the amount of kernel code executing via the firmware's 1:1 mapping is rather small and limited to the .head.text region. So let's drop the NX restrictions only on that subregion, but not before remapping it as read-only first. 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.