Because of NixOS's generate-config.pl tries to answer 'M' to as much
configs as possible, this exposes the wrong Kconfig in the RPi-specific
code which is added in the new kernel tree intended to support RPi 5.
Add kernel patches to fix the Kconfig, which results in the relavant
part being disabled on the RPi 3 build of the kernel.
The 1.75 patch can't be fetched, because it doesn't apply. But git
can apply it cleanly, so it must just need to do a three-way merge or
something. Regardless, we need to include a version that patch(1) can
apply in Nixpkgs.
Borrowing from here to match hardened profile with more recent kernels:
* https://madaidans-insecurities.github.io/guides/linux-hardening.html?#boot-parameters
* https://github.com/a13xp0p0v/kernel-hardening-checker/
Removed "slub_debug" as that option disables kernel memory address
hashing. You also see a big warning about this in the dmesg:
"This system shows unhashed kernel memory addresses via the console, logs, and other interfaces."
"init_on_alloc=1" and "init_on_free=1" zeroes all SLAB and SLUB allocations. Introduced in 6471384af2a6530696fc0203bafe4de41a23c9ef. Also the default for the Android Google kernel btw. It is on by default through the KConfig.
"slab_nomerge" prevents the merging of slab/slub caches. These are
effectively slab/slub pools.
"LEGACY_VSYSCALL_NONE" disables the older vsyscall mechanic that relies on
static address. It got superseeded by vdsos a decade ago. Read some
LWN.net to learn more ;)
"debugfs=off" I'm sure there are some few userspace programs that rely on
debugfs, but they shouldn't.
Most other things mentioned on the blog where already the default on a
running machine or may not be applicable.
Most other Kconfigs changes come from the kernel hardening checker and
were added, when they were not applied to the kernel already.
Unsure about CONFIG_STATIC_USERMODEHELPER. Would need testing.
