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vphone-cli/research/kernel_patch_jb/patch_spawn_validate_persona.md
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B14 patch_spawn_validate_persona

Verdict

  • Preferred upstream reference: /Users/qaq/Desktop/patch_fw.py.
  • Final status on PCC 26.1 research: match upstream.
  • Upstream patch sites:
    • 0x00FA7024 -> nop
    • 0x00FA702C -> nop
  • Final release-variant analogue:
    • 0x00F6B024 -> nop
    • 0x00F6B02C -> nop
  • Previous repo drift to 0x00FA694C / branch rewrite is now rejected for this patch because it did not match upstream and targeted an outer gate rather than the smaller helper that actually contains the sibling nil-field rejects.

Anchor Class

  • Primary runtime anchor class: string anchor.
  • Concrete anchor: "com.apple.private.spawn-panic-crash-behavior" in the outer spawn policy wrapper.
  • Secondary discovery: semantic enumeration of that wrapper's local BL callees to find the unique small helper that matches the upstream control-flow shape.
  • Why this survives stripped kernels: the matcher does not need IDA names or embedded symbols; it only needs the in-image entitlement string plus decoded local CFG in the nearby helper.

Final Patch Sites

PCC 26.1 research

  • 0xFFFFFE0007FAB024 / 0x00FA7024: cbz w8, ... -> nop
  • 0xFFFFFE0007FAB02C / 0x00FA702C: cbz w8, ... -> nop

PCC 26.1 release

  • 0x00F6B024: cbz w8, ... -> nop
  • 0x00F6B02C: cbz w8, ... -> nop

Why These Gates Are Correct

Facts from IDA / disassembly

The upstream-matching helper contains the local block:

ldr w0, [x20]
bl  ...
cbz x0, fail_alt
ldr w8, [x21, #0x18]
cbz w8, continue
ldr w8, [x20, #8]
cbz w8, deny      ; patched
ldr w8, [x20, #0xc]
cbz w8, deny      ; patched
mov x8, #0
ldr w9, [x19, #0x490]
add x10, x0, #0x140
casa x8, x9, [x10]

Both patched cbz instructions jump to the same deny-return block.

Facts from XNU semantics

This helper is a compact persona validation subroutine in the spawn/exec policy path. The two sibling cbz guards are the local nil / missing-field reject gates immediately before the helper proceeds into the proc-backed persona state update path.

Conclusion

The upstream pair is the correct semantic gate because:

  • it is the exact pair patched by the known-good upstream tool,
  • both branches converge on the helper's deny path,
  • they live in the small validation helper reached from the outer spawn entitlement wrapper,
  • and they are narrower and more precise than the previously drifted outer tbz bypass.

Match vs Divergence

  • Upstream relation: match.
  • Explicitly rejected divergence: outer branch rewrite at 0x00FA694C / 0x00F6A94C.
  • Why rejected: although that outer gate also affects persona validation, it is broader than the upstream helper-local reject sites and was not necessary once the true upstream helper was recovered.

Reveal Procedure

  1. Find the outer spawn policy wrapper by the in-image entitlement string "com.apple.private.spawn-panic-crash-behavior".
  2. Enumerate BL callees inside that wrapper.
  3. Keep only small local helpers.
  4. Select the unique helper whose decoded CFG contains:
    • ldr [arg,#8] ; cbz deny
    • ldr [arg,#0xc] ; cbz deny
    • shared deny target
    • nearby ldr [x19,#0x490] ; ... ; casa sequence.
  5. Patch both helper-local cbz instructions with NOP.

Validation

  • PCC 26.1 research dry-run: hit at 0x00FA7024 and 0x00FA702C
  • PCC 26.1 release dry-run: hit at 0x00F6B024 and 0x00F6B02C
  • Match verdict vs /Users/qaq/Desktop/patch_fw.py: match

Files

  • Patcher: scripts/patchers/kernel_jb_patch_spawn_persona.py
  • Analysis doc: research/kernel_patch_jb/patch_spawn_validate_persona.md

2026-03-06 Rework

  • Upstream target (/Users/qaq/Desktop/patch_fw.py): match.
  • Final research sites: 0x00FA7024 (0xFFFFFE0007FAB024) and 0x00FA702C (0xFFFFFE0007FAB02C).
  • Anchor class: string. Runtime reveal starts from the stable entitlement string "com.apple.private.persona-mgmt", resolves the small helper, and matches the exact upstream dual-cbz pair on the [x20,#8] / [x20,#0xc] slots.
  • Why this site: it is the exact known-good upstream zero-check pair inside the persona validation helper. The previous drift to 0x00FA694C patched a broader exec-path branch and did not match the upstream helper or XNU spawn_validate_persona(...) logic.
  • Release/generalization rationale: entitlement strings are stable across stripped kernels, and the dual-load/dual-cbz shape is tiny and source-backed.
  • Performance note: one string-xref resolution plus a very small helper-local scan.
  • Focused PCC 26.1 research dry-run: hit, 2 writes at 0x00FA7024 and 0x00FA702C.