A limitation of the current implementation of SGX IPFS in WAMR is that
it prevents to open files which are not in the current directory.
This restriction is lifted and can now open files in paths, similarly to the
WASI openat call, which takes into account the sandbox of the file system.
This PR integrates an Intel SGX feature called Intel Protection File System Library (IPFS)
into the runtime to create, operate and delete files inside the enclave, while guaranteeing
the confidentiality and integrity of the data persisted. IPFS can be referred to here:
https://www.intel.com/content/www/us/en/developer/articles/technical/overview-of-intel-protected-file-system-library-using-software-guard-extensions.html
Introduce a cmake variable `WAMR_BUILD_SGX_IPFS`, when enabled, the files interaction
API of WASI will leverage IPFS, instead of the regular POSIX OCALLs. The implementation
has been written with light changes to sgx platform layer, so all the security aspects
WAMR relies on are conserved.
In addition to this integration, the following changes have been made:
- The CI workflow has been adapted to test the compilation of the runtime and sample
with the flag `WAMR_BUILD_SGX_IPFS` set to true
- Introduction of a new sample that demonstrates the interaction of the files (called `file`),
- Documentation of this new feature
