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zqxwceandClaude Opus 4.8
c22da90929
iOS 27 userland on the 26.4 vphone600 kernel had SpringBoard crash-looping
with no display. Root cause: the IOKit user-client open path runs TWO
independent MAC gates -- a MACF-aggregator check (already patched by
patchIoucFailedMacf) and a separate Sandbox check -- and the Sandbox gate
spuriously DENIES the render server (backboardd) its opens of
IOMobileFramebufferUserClient / IOSurfaceRootUserClient / IOHIDEventService.
27-specific: absent on a native 26.4 userland. Denied the framebuffer,
backboardd can't present (no Apple logo) and vends no main display, so
FBSDisplayMonitor asserts on a nil mainDisplay -> crash-loop.
Add patchIoucFailedSandbox (KernelJBPatchIoucSandbox.swift), mirroring
patchIoucFailedMacf: anchor on the "IOUC %s failed sandbox in process %s"
string, find the deny block (the CBNZ target enclosing the fail-log ADRP),
and rewrite its first instruction with an unconditional B to the
NotPermitted allow-proceed target. Structural anchors only, no hardcoded
offsets. No-op where the gate already allows (native 26.x userlands).
Verified: backboardd opens the framebuffer, SpringBoard runs (0 crashes),
display enumerates (LCD/primary), [CADisplay mainDisplay] resolves, and the
guest GUI renders (confirmed visible over VNC).
Disable three earlier wrong-theory display patches (kept in-tree, off in
findAll, for the record):
- patchParavirtDisplayPrimary: setting primary=1 is actively HARMFUL on 27
-- it becomes the display NAME suffix ("primary-1") and breaks the render
server's exact-name match.
- patchIomfbSwapEnd{VariableSize,HandlerSize}: iOS 27 never uses IOMFB
method 5 (SwapEnd) for present -- confirmed by kernel trace of the real
handler (cmp w2,#0x588) with SpringBoard actively presenting -- so these
are irrelevant on 27 and would break 26.x's native 0x588 SwapEnd.
SwapEnd userland DSC size patch made per-base (cfw_install*, cfw.py,
cfw_patch_iomfb_swapend.py): 26.x validated, harmless on 27.
research/0_binary_patch_comparison.md updated (JB-10b added for the sandbox
gate; JB-02c corrected to disabled/wrong-theory).
Still open: the normal (VZ) render path stays black even though the guest
presents (VNC works) -- 27 uses a present mechanism the 26.4 paravirt-GPU
path doesn't receive. Tracked separately for follow-up.
Co-Authored-By: Claude Opus 4.8 <[email protected]>