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Make explicit hash signature partitions - #88
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bfjelds (bfjelds) wants to merge 4 commits into
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part_alignmentandblocksaren’t explicit in the file itself. Since the… · New
What changed in this PR
Splits the existing /usr dm-verity HASH partitions into separate HASH and reserved HASH-SIG partitions to enable future verity root-hash signatures, and updates partition type resolution/documentation accordingly.
Changes:
- Added a new DPS partition type placeholder (
dps-usr-verity-sig) with architecture-specific GUIDs. - Updated UKI disk layout to split HASH into HASH + HASH-SIG partitions and renumber subsequent partitions/references.
- Documented the new reserved HASH-SIG partition in ACL architecture docs.
| File | Description |
|---|---|
| build_library/disk_util | Adds GUID mapping and placeholder resolution for the new signature partition type. |
| build_library/disk_layout_uki.json | Splits HASH-A/B into HASH + HASH-SIG, adjusts sizing/alignment, and renumbers partitions/references. |
| acl/docs/architecture.md | Documents the new reserved HASH-SIG partition following HASH-A. |
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|-, which typically won’t render as a proper Markdown list item. Consider… · Newpart_alignmentandblocksaren’t explicit in the file itself. Since the…_commentis very long and also relies on implicit units (e.g., why2048equals 1 MiB). To… · New
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🔵 Needs a closer look
The shipped partition-layout changes still require an actual image build and boot/kola validation before human approval.
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Resolved since last review (7)
|-, which typically won’t render as a proper Markdown list item. Consider…part_alignmentandblocksaren’t explicit in the file itself. Since the…_commentis very long and also relies on implicit units (e.g., why2048equals 1 MiB). To…
Paco Huelsz (frhuelsz)
approved these changes
Oct 5, 2026
…tion Replace the single 10 MiB HASH-A/HASH-B partitions with two partitions each: HASH-A/HASH-B (exact 9 MiB, verity hash tree, dps-usr-verity) and HASH-SIG-A/HASH-SIG-B (exact 1 MiB, reserved for a future verity root-hash signature, dps-usr-verity-sig). Add DPS_USR_VERITY_SIG_GUIDS to disk_util alongside the existing DPS_USR_VERITY_GUIDS constants, using the official UAPI Discoverable Partitions Specification GUIDs for the usr-verity-sig partition type (x86_64 and aarch64), so the new partitions are resolved the same way as the existing verity/root types instead of using the generic data GUID. Total space per slot is unchanged; subsequent partitions (OEM, ROOT) and all verity_hash/layout references are renumbered accordingly.
disk_util aligns every partition start up to part_alignment (4096 blocks/2MiB) before placing it. Because HASH-A/HASH-B (18432 blocks = 9 MiB) and HASH-SIG-A/HASH-SIG-B (2048 blocks = 1 MiB) are not themselves multiples of 4096, the default alignment silently inserted four 1 MiB padding gaps (before each HASH-SIG and before USR-B/OEM) that belong to no partition and cannot be used - 4 MiB of dead space per disk image, contradicting the intent that splitting HASH into HASH+HASH-SIG not change total footprint. Override part_alignment to 2048 (1 MiB) on HASH-SIG-A/B specifically: they do not need 2 MiB alignment (small, non-performance-sensitive signature partitions), and since HASH-A + HASH-SIG-A (9 MiB + 1 MiB = 10 MiB) is itself a 2 MiB multiple, this removes the gap with no other side effects - every downstream partition offset (USR-B, HASH-B, HASH-SIG-B, OEM, ROOT) and the final disk image size now exactly match the original pre-split layout. Verified via disk_util.LoadPartitionConfig: zero gaps, and every partition offset after HASH-A matches the pre-split baseline exactly.
- disk_layout_uki.json: expand HASH-A/_B _comment with verity hash tree sizing rationale (sha256 + 4096-byte blocks assumption, ~8.08 MiB computed size vs 9 MiB allocated). Clarify blocks/part_alignment units are 512-byte sectors on the new HASH-SIG-A/B entries. - architecture.md: split the HASH-A/HASH-SIG-A bullet into two for readability.
The usr-hash-sig-a/b partitions shift ROOT from the 7th to the 9th partition on the new layout. Hard-coding `nbd0p7` and `max_part=8` broke the documented verification steps. Select ROOT by GPT partition label instead of a hard-coded index, so the commands work for both the old and new layouts. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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trident is now pulled from azure-container-linux/acl/SPECS/trident, which has support for hash-signature existance. |
aadhar-agarwal
approved these changes
Oct 8, 2026
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Summary
Split bigger HASH partitions into more appropriately sized HASH and HASH-SIGN partitions to enable hash signatures.
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Does this affect the image build?
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