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rosco-m68k / rosco_m68k

Design, documentation and software for the Really Old School Computer (M68K)
https://rosco-m68k.com
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Fix `LOAD` segments having RWX permissions #350

Closed 0xTJ closed 1 year ago

0xTJ commented 1 year ago

This PR fixes the ld warnings reported by Xark on Discord, such as:

warning: starter_c.elf has a LOAD segment with RWX permissions

This is caused by there being LOAD segments in the generated program that have both write and execute permissions, which could facilitate security exploits in programs. While these warnings are harmless here (we don't have an MMU yet to enforce permissions anyways), they are annoying. They can be suppressed with --no-warn-rwx-segment added to LDFLAGS, but this only hides the issue.

In this PR, I fix a couple few assembly files where the sections weren't being set to the right type. In vasm, the data is equivalent to section .data,data, instead of section .data. The former sets the section to have the properties of a data section, instead of a text one. This change prevents the .data and .bss from themselves becoming RWX.

The second cause of the issue here is that both text and data were being placed in the same pages in memory, which causes those pages to have permissions that are the union of those sections' permissions. To fix this, maximum-page-size-alignment is added between the text and data, to allow the linker to assign them different permissions.

Originally this wasted up to 0x1FFF bytes of space in the binaries, but this was fixed by overriding the maximum page size to a smaller value. This will break loading in a system using an MMU, but saves considerable space. By default, this space saving is disabled for the '030, '040, and '060, which have version that include an MMU.

XarkLabs commented 1 year ago

I tried this yesterday and it seemed to work great.