clarify PCC fault vs instruction access fault #495
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jrtc27
reviewed
Dec 21, 2024
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| ^1^ The higher priority CHERI <<cheri_pte_ext,PTE>> page fault covers capability loads or atomics where the loaded tag _is not_ checked, and all capability stores and atomics where the stored tag is set. | ||
| ^1^ PCC bounds are intended to be checked against all the bytes of fetched instructions. | ||
| In the case of variable length instruction encoding, and that the fetch has failed to return any data, then only a minimum length instruction is checked against the PCC bounds. |
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This sounds a lot like “fetch the whole instruction and only then check bounds” which can be dangerous wrt side channels
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fixes #494
@tomaird
the diff is a bit confused as a renumbered the notes below the table
the only real addition is the new note number 1