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[discrete]
= CHERI CAP LIB

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The https://github.com/CTSRD-CHERI/cheri-cap-lib[cheri-cap-lib] repository
provides an RTL API for CHERI capabilities, as well as a reference
implementation of it. It aims to serve as a central implementation providing
various wrappers to avoid the need for multiplicity of implementation efforts.
This is particularly desirable when considering the verification work already
spent and the overall tricky nature of the algorithms involved.

The explicit goal of CHERI CAP LIB is to provide a set of relatively low level
operations to interact with CHERI capabilities, and allow the user to abstract
away the specifics of the published
https://www.cl.cam.ac.uk/research/security/ctsrd/pdfs/2019tc-cheri-concentrate.pdf[capability format]
and its subsequent iterations as much as reasonably possible. Other
implementations could easily comply with the CHERI CAP LIB API.

The CHERI CAP LIB API is here to guaranty that subtleties in capability
manipulations are handled correctly. This means that direct bit manipulation on
CHERI capabilities bypassing the provided functions are greatly discouraged as
they will very easily lead to nonsense capabilities. For this reason, the CHERI
CAP LIB API is more in the style of a set of accessors (java interface / haskell
typeclass, etc...) than in that of a simple struct-style interface with direct
field manipulation. Again, this is deliberate and necessary to easily enforce
well behaved capability manipulations.

Currently, the implementation of the API is in Bluespec System Verilog and
wrappers are available in Verilog and Blarney.

[discrete]
== Contents

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== The CHERI CAP LIB API
[source, bsv]
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function Bool isValidCap (t cap);
function t setValidCap (t cap, Bool valid);
function Bit#(flg) getFlags (t cap);
function t setFlags (t cap, Bit#(flg) flags);
function HardPerms getHardPerms (t cap);
function t setHardPerms (t cap, HardPerms hardperms);
function SoftPerms getSoftPerms (t cap);
function t setSoftPerms (t cap, SoftPerms softperms);
function Bit#(31) getPerms (t cap);
function t setPerms (t cap, Bit#(31) perms);
function Kind getKind (t cap);
function Bool isSentry (t cap);
function Bool isSealedWithType (t cap);
function Bool isSealed (t cap);
function Bit#(ot) getType (t cap);
function Exact#(t) setType (t cap, Bit#(ot) otype);
function Bit#(n) getAddr (t cap);
function Exact#(t) setAddr (t cap, Bit#(n) addr);
function t maskAddr (t cap, Bit#(maskable_bits) mask);
function Bit#(n) getOffset (t cap);
function Exact#(t) modifyOffset (t cap, Bit#(n) offset, Bool doInc);
function Exact#(t) setOffset (t cap, Bit#(n) offset);
function Exact#(t) incOffset (t cap, Bit#(n) inc);
function Bit#(n) getBase (t cap);
function Bit#(TAdd#(n, 1)) getTop (t cap);
function Bit#(TAdd#(n, 1)) getLength (t cap);
function Bool isInBounds (t cap, Bool isTopIncluded);
function Exact#(t) setBounds (t cap, Bit#(n) length);
function t nullWithAddr (Bit#(n) addr);
function t almightyCap;
function t nullCap;
function Bool validAsType (t dummy, Bit#(n) checkType);
function t fromMem (Tuple2#(Bool, Bit#(mem_sz)) mem_cap);
function Tuple2#(Bool, Bit#(mem_sz)) toMem (t cap);
----