Re: [PATCH] m68k: Implement kernel memory protection

[Michael Schmitz]

Daniel,

it might be possible to fix up the last (partially used) descriptor from 
C code, if there's a limit field. I find the head.S assembly too much of 
a headache to change, but that would certainly be safer.

Wasting up to 256 kB is a pain on 030. Maybe rather skip protecting the 
last section?

(* ducks ... *)

Cheers,

    Michael

On 18/11/25 11:01, Daniel Palmer wrote:
> Hi Michael,
>
> On Tue, 18 Nov 2025 at 02:41, Michael Schmitz <schmitzmic@xxxxxxxxx> wrote:
> > Daniel,
> >
> > take a look at arch/m68k/kernel/head.S - 030 MMU setup uses early
> > termination descriptors for kernel memory, _not_ regular page tables.
> Yeah, so when setting write protect on the last bit of either the text
> or the rodata the end is getting rounded up to the next 256KB and
> write protecting too much.
> I worked that out and adding some alignment in the linker script so
> that everything after the places getting write protected is pushed off
> to the next 256KB does fix it but wastes some memory.
> Looking at the manual for the 68030 it seems like early termination
> descriptors can have a limit so I could set the alignment, fix up the
> limit and then give the wasted memory back. But we are using the short
> format that doesn't have the limit field.
>
> Cheers,
>
> Daniel