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Fully apply implicit acperm, including tag clear - #9
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arichardson
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Apr 16, 2025
| let restrictCL = loaded_cap.tag & not(canEL(auth_cap)); | ||
| if restrictCL then {loaded_cap with cl = auth_cap.cl & loaded_cap.cl} else loaded_cap | ||
| if restrictCL | clearWLM | clearEL then { | ||
| clearTagAcperm(loaded_cap) |
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This seems wrong, we should not zero the tag on sealed if all we did was restrict CL.
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The spec says that restricting CL is done with an implicit ACPERM, even if you don't do clear EL too.
"implicit ACPERM" means do the whole instruction, as discussed in the linked ticket.
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Yeah my view is that this is incorrect and should be fixed in the spec.
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@arichardson do you know if this was fixed in the spec?
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I'm archiving this repo but we can continue the discussion here.
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Implicit ACPERMs, done for permission-clearing on loads, should apply the full instruction semantics, including clearing the tag for certain cases.
Raised from this issue: riscv/riscv-cheri#577
While the spec may change on this, the issue clarified the intention was always that the full ACPERM semantics should be applied, so the model was always wrong on this.