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SPRR index constraints during sptm_map_page

Determine the constraints SPTM enforces on SPRR index values during map_page operations and derive the mapping between SPRR indices and effective permissions on contemporary A15/M2-class systems.

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Background

SPTM performs validations on new page table entries, including constraints related to SPRR indices based on table frame types. The authors could not conclusively explain these mechanisms due to a lack of current SPRR index-to-permission mapping.

Establishing these constraints is critical to understanding how SPTM prevents unauthorized changes in access and execute rights.

References

We cannot provide a conclusive understanding of these mechanisms at this time, as we would require a current and up-to-date mapping of SPRR indices for this.

— Modern iOS Security Features -- A Deep Dive into SPTM, TXM, and Exclaves (2510.09272 - Steffin et al., 10 Oct 2025) in Section SPTM Page Mapping — Further Validations