Implement SGX getrandom/getentropy without ocall

[wenyongh]

Implement SGX getrandom with sgx_read_rand and getentropy with rdseed instruction
instead of ocall to improve the security.

[zhenghaven]

The new getrandom implementation looks good to me. However, for getentropy, I'm not sure if using sgx_read_rand is secure enough for the entropy, since sgx_read_rand uses RDRAND instruction (reference: https://github.com/intel/linux-sgx/blob/master/external/rdrand/src/rdrand.c and https://github.com/intel/linux-sgx/blob/master/common/src/sgx_read_rand.cpp). Probably RDSEED instruction is a better option for entropy. As far as I know, Intel SGX SDK does not provide a high-level API to RDSEED instruction, but RDSEED instruction itself should be available inside of SGX. And I found Intel provides some sample code for using the RDSEED instruction: https://www.intel.com/content/www/us/en/developer/articles/guide/intel-digital-random-number-generator-drng-software-implementation-guide.html

[wenyongh]

The new getrandom implementation looks good to me. However, for getentropy, I'm not sure if using sgx_read_rand is secure enough for the entropy, since sgx_read_rand uses RDRAND instruction (reference: https://github.com/intel/linux-sgx/blob/master/external/rdrand/src/rdrand.c and https://github.com/intel/linux-sgx/blob/master/common/src/sgx_read_rand.cpp). Probably RDSEED instruction is a better option for entropy. As far as I know, Intel SGX SDK does not provide a high-level API to RDSEED instruction, but RDSEED instruction itself should be available inside of SGX. And I found Intel provides some sample code for using the RDSEED instruction: https://www.intel.com/content/www/us/en/developer/articles/guide/intel-digital-random-number-generator-drng-software-implementation-guide.html

Thanks, code of getentropy was updated by using rdseed instruction.

[zhenghaven]

It compiles and works on my end. Thank you for addressing this issue!