I hereby relicense all my work on Sortix under the ISC license as below.
All Sortix contributions by other people are already under this license,
are not substantial enough to be copyrightable, or have been removed.
All imported code from other projects is compatible with this license.
All GPL licensed code from other projects had previously been removed.
Copyright 2011-2016 Jonas 'Sortie' Termansen and contributors.
Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
Enable the NX bit on x86_64 and set if not PROT_EXEC and enable the write
protection mode (CR0.WP) that disables the default behavior where the kernel
is able to write to read-only memory. Fix kernel broken assumptions it can
access read-only memory and take care to never set PROT_KWRITE on user-space
pages unless PROT_WRITE is also set, otherwise user-space will be able to
write to read-only memory.
This achieves X^W in the whole system except for the core kernel itself as
it is currently don't know the purpose of pages when identity mapping the
first 4 MiB.
This fixes a rather nasty issue where gcc's garbage collection triggered a
munmap call with the effect that it began unmapping huge amounts of kernel
data until the system triple faulted.
