The 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 capability format and its subsequent iterations as much as reasonably possible. Other implementations should easily be able to comply with the CHERI CAP LIB API. In particular, implementations exploring alterations to the underlying capability format will benefit from adhering to this API for easy integration with codebases already making use of the exisitng CHERI capability implementation. If some genuinely new behaviour is necessary, generalising the CHERI CAP API should be considered.
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.
cheri-cap-lib supports being used as a generator within FuseSoC. The scripts
and cores for this are within the fusesoc directory, and the file
cheri-cap-lib-test.core shows how a core can declare a dependency on and
use the cheri-cap-lib generator.
The FuseSoC generator will generate Verilog modules for each of the functions
in CHERICapWrap.bsv, as well as a SystemVerilog package and module to
make working with these modules slightly simpler in SystemVerilog.
To generate both the 64bit and 128bit wrappers and packages, run
fusesoc --cores-root . run --target test --setup ucam:cheri:cheri-cap-lib-test
The files will be generated in
build/ucam_cheri_cheri-cap-lib-test_0/src/ucam_cheri_cheri-cap-lib-verilog-autogen-64_0/
and
build/ucam_cheri_cheri-cap-lib-test_0/src/ucam_cheri_cheri-cap-lib-verilog-autogen-128_0/
These fusesoc cores and instructions work using fusesoc 0.3 as installed
by running
pip3 install -r python_requirements.txt
within the OpenTitan GitHub repository as of commit
https://github.com/lowRISC/opentitan/commit/2438b17afe4fef0d815be2e890763c288c449918