[imm_rom_ext] Add immutable ROM_EXT ePMP reconfiguration #25310
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@sasdf I think this can be re-based now and marked ready for review |
Reconfigure ePMP in immutable ROM_EXT to remove executable permission on the immutable data segment. Now, ePMP will be reconfigured to the following layout before jumping to the mutable ROM_EXT: ``` * 6: MU_EXT ----- ---- * 7: MU_EXT TOR LX-R * 8: IM_EXT ----- ---- * 9: IM_EXT TOR LX-R * 10: VIRTUAL NAPOT L--R * 11: STACK NA4 L--- ``` MU_EXT stands for mutable part of rom_ext, and IM_EXT is the immutable part. Slot 10 will be empty if address translation is not enabled, and stack guard is added back to slot 11. Before jumping to Owner SW, all lock bits will be cleared, so all entries can be recycled by Owner SW. Owner SW will be placed at the same entries as before (2, 3, 4). Change-Id: Id9b6cd68cc24a5816d3e3dc8374b5533a7c6eb75 Signed-off-by: Yi-Hsuan Deng <[email protected]>
timothytrippel
approved these changes
Jan 8, 2025
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The immutable ROM_EXT data segment is also covered in ROM_EXT code region due to ROM limitation,
This PR let immutable ROM_EXT reconfigure ePMP first to remove executable permission on the data segment.
Jumping from IMM_ROM_EXT -> ROM / mutable ROM_EXT
We propose to use the following new ePMP layout before jumping to the mutable ROM_EXT:
MU_EXT stands for mutable part of rom_ext text segment, and IM_EXT is the immutable part.
Slot 10 will be empty if address translation is not enabled, and stack guard
is added back to slot 11.
Slot 12 and 13 are also swapped, so that the chip in production LCS has one more contiguous free entry.
Jumping from ROM_EXT -> Owner SW
Before jumping to Owner SW, all lock bits will be cleared, so all entries can
be reclaimed by Owner SW. Entries 8 ~ 11 ( &12 in prod LCS ) can be safely reconfigure by Owner SW.
Owner SW ePMP will be placed at the entries 2, 3 and 4 same as before.
When the rom_ext is linked directly to the immutable lib instead of prebuilt immutable section, the IM_EXT region (6 & 7) will covers whole ROM_EXT text section. This is the current behavior since prebuilt section is not ready yet.