Hi all- After an offline discussion with Sean yesterday, here are some updates to the user API parts of my proposal. Unfortunately, Sean convinced me that MAXPERM doesn't work the way I described it because, for SGX2, the enclave loader won't know at load time whether a given EAUG-ed page will ever be executed. So here's an update. First, here are the requrements as I see them, where EXECUTE, EXECMOD, and EXECMEM could be substituted with other rules at the LSM's discretion: - You can create a WX or RWX mapping if and only if you have EXECMEM. - To create an X mapping of an enclave page that has ever been W, you need EXECMOD. - To create an X mapping of an enclave page that came from EADD, you need EXECUTE on the source file. Optionally, we could also permit this if you have EXECMOD. And I have two design proposals. One is static and one is dynamic. To implement either one, we will probably need a new .may_mprotect vm operation, and that operation can call an LSM hook. Or we can give LSMs a way to detect that a given vm_area_struct is an enclave. As I see it, this is an implementation detail that is certainly solveable. Static proposal: EADD takes an execute_intent flag. It calls a new hook: int security_enclave_load(struct vm_area_struct *source, bool execute_intent); This hook will fail if execute_intent==true and the caller has neither EXECUTE, EXECMOD, nor EXECMEM. EAUG sets execute_intent = false. EINIT takes a sigstruct pointer. SGX can (when initially upstreamed or later on once there's demand) call a new hook: security_enclave_init(struct sigstruct *sigstruct, struct vm_area_struct *source); mmap() and mprotect() will require EXECMEM to create WX or RWX mappings. They will require EXECMOD to create RX or X mappings of an execute_intent==false page. They require no permissions in the other cases. Dynamic proposal: EADD does not take any special flags. It does something like this internally: bool execute_intent = true; int security_enclave_load(struct vm_area_struct *source, bool *execute_intent); The implementation of security_enclave_load() may set *execute_intent to false. The driver records execute_intent after the LSM is done. mmap() and mprotect() will require EXECMEM to create WX or RWX mappings. They will require EXECMOD to create RX or X mappings of an execute_intent==false page. They require no permissions in the other cases. A benefit of the static proposal is that audit failures due to a lack of EXECUTE permission are easy to implement and to understand in the lods. With the dynamic model, we can only really audit the lack of EXECMOD or EXECMEM. A benefit of the dynamic model is that we hide what is arguably a decently large wart from the API.
