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Semantics of RETYPE_Flag_Structure modifications to Frame Table Entries

Characterize the semantics and effects of the RETYPE_Flag_Structure used during SPTM retype operations, including how the retrieved type-specific flag alters the Frame Table Entry (FTE) and which frame parameters are modified for the new frame type.

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Background

During retype, SPTM retrieves a type-specific entry from a structure the authors denote RETYPE_Flag_Structure and then alters the FTE based on that flag. The authors cannot yet explain the exact effect of this alteration.

Understanding these flag-driven changes is essential to comprehending how SPTM enforces type semantics and state transitions on physical frames.

References

The exact workings of this are still unclear, but we assume it will alter frame parameters if necessary for the new frame type.

— Modern iOS Security Features -- A Deep Dive into SPTM, TXM, and Exclaves (2510.09272 - Steffin et al., 10 Oct 2025) in Section “SPTM Frame Retyping — In-Depth”, subsection “Handling Retyping Requests”