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El perm sealed #460

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merged 2 commits into from
Dec 3, 2024
Merged

El perm sealed #460

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be4860d
clarify that EL-perm is only stripped if unsealed
tariqkurd-repo Dec 3, 2024
6bfe29b
clarify that EL-perm is only stripped if unsealed
tariqkurd-repo Dec 3, 2024
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4 changes: 1 addition & 3 deletions src/insns/load_tag_perms.adoc
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Expand Up @@ -3,9 +3,7 @@ The tag value written to `cd` is 0 if the tag of the memory location loaded is
0 or the authorizing capability (<<ddc>> or `cs1`) does not grant <<c_perm>>.
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If the authorizing capability does not grant <<lm_perm>>, and the tag of `cd` is 1 and `cd` is not sealed, then an implicit <<ACPERM>> clearing <<w_perm>> and <<lm_perm>> is performed to obtain the intermediate permissions on `cd`.
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If the authorizing capability does not grant <<el_perm>>, and the tag of `cd` is 1, then an implicit <<ACPERM>> clearing <<el_perm>> and restricting the <<section_cap_level>> to the level of the authorizing capability is performed to obtain the final permissions on `cd`.
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This broke the formatting here. We've lost a paragraph break.

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ahhh

If the authorizing capability does not grant <<el_perm>>, and the tag of `cd` is 1, then an implicit <<ACPERM>> restricting the <<section_cap_level>> to the level of the authorizing capability is performed.
If `cd` is not sealed, this implicit <<ACPERM>> also clears <<el_perm>> to obtain the final permissions on `cd` (see <<cap_level_load_summary>>).

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3 changes: 2 additions & 1 deletion src/level-ext.adoc
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Expand Up @@ -48,7 +48,8 @@ With `LVLBITS=1` there is a single bit comparison, so it behaves as follows:
NOTE: For `LVLBITS=1` this permission is equivalent to _StoreLocal_ in CHERI v9, Morello and CHERIoT.

[#el_perm,reftext="EL-permission"]
Elevate Level Permission (EL):: Any capability with its tag set to 1 that is loaded from memory has its <<el_perm>> cleared and its <<section_cap_level>> restricted to the authorizing capability's <<section_cap_level>> if the authorizing capability does not grant <<el_perm>>.
Elevate Level Permission (EL):: Any unsealed capability with its tag set to 1 that is loaded from memory has its <<el_perm>> cleared and its <<section_cap_level>> restricted to the authorizing capability's <<section_cap_level>> if the authorizing capability does not grant <<el_perm>>.
If sealed, then only <<section_cap_level,CL>> is modified, <<el_perm>> is unchanged.
This permission is similar to the existing <<lm_perm>>, but instead of applying to the <<w_perm>> on the loaded capability it restricts the <<section_cap_level,CL>> field.


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