x86/sgx: Support adding of pages to an initialized enclave
With SGX1 an enclave needs to be created with its maximum memory demands allocated. Pages cannot be added to an enclave after it is initialized. SGX2 introduces a new function, ENCLS[EAUG], that can be used to add pages to an initialized enclave. With SGX2 the enclave still needs to set aside address space for its maximum memory demands during enclave creation, but all pages need not be added before enclave initialization. Pages can be added during enclave runtime. Add support for dynamically adding pages to an initialized enclave, architecturally limited to RW permission at creation but allowed to obtain RWX permissions after trusted enclave runs EMODPE. Add pages via the page fault handler at the time an enclave address without a backing enclave page is accessed, potentially directly reclaiming pages if no free pages are available. The enclave is still required to run ENCLU[EACCEPT] on the page before it can be used. A useful flow is for the enclave to run ENCLU[EACCEPT] on an uninitialized address. This will trigger the page fault handler that will add the enclave page and return execution to the enclave to repeat the ENCLU[EACCEPT] instruction, this time successful. If the enclave accesses an uninitialized address in another way, for example by expanding the enclave stack to a page that has not yet been added, then the page fault handler would add the page on the first write but upon returning to the enclave the instruction that triggered the page fault would be repeated and since ENCLU[EACCEPT] was not run yet it would trigger a second page fault, this time with the SGX flag set in the page fault error code. This can only be recovered by entering the enclave again and directly running the ENCLU[EACCEPT] instruction on the now initialized address. Accessing an uninitialized address from outside the enclave also triggers this flow but the page will remain inaccessible (access will result in #PF) until accepted from within the enclave via ENCLU[EACCEPT]. Signed-off-by:Reinette Chatre <reinette.chatre@intel.com> Signed-off-by: