On Wed, Mar 11, 2020 at 03:28:32PM +0200, Jarkko Sakkinen wrote: > On Thu, Mar 05, 2020 at 01:33:28PM +0200, Jarkko Sakkinen wrote: > > On Wed, 2020-03-04 at 14:27 -0500, Nathaniel McCallum wrote: > > > > > +xsave_area: > > > > + .fill 1, 4, 0x037F # FCW > > > > + .fill 5, 4, 0 > > > > + .fill 1, 4, 0x1F80 # MXCSR > > > > + .fill 1, 4, 0xFFFF # MXCSR_MASK > > > > + .fill 123, 4, 0 > > > > + .fill 1, 4, 0x80000000 # XCOMP_BV[63] = 1, compaction mode > > > > + .fill 12, 4, 0 > > > > > > I find this much more readable: > > > > And I always aim to get things more readable. Thank you. > > > > > xsave_area: > > > # Legacy > > > .fill 1, 4, 0x037F # FCW > > > .fill 5, 4, 0 > > > .fill 1, 4, 0x1F80 # MXCSR > > > .fill 1, 4, 0xFFFF # MXCSR_MASK > > > .fill 60, 8, 0 > > > > > > # Header > > > .fill 1, 8, 0 # XSTATE_BV > > > .fill 1, 8, 1 << 63 # XCOMP_BV (compaction mode) > > > .fill 6, 8, 0 > > > > > > Also, since people are likely to copy this code for their own > > > enclaves, it would be helpful to document which flags are set in FCW > > > and MXCSR. > > > > It was meant as a test program but I'd guess what you say is true > > because it also might be the only alternative user space to Intel's > > :-) And a great starting point if you want to do things from scratch. > > > > Because I meant it as a smoke test program for SGX, not everything is > > too well documented but given the multipurpose use for that code I'll > > make the improvements that you are suggesting. > > For FPU Control World (FCW), I think 0x037F is not the right value even > if section 18.5 in the x86 SDM says that it is the initial value for it. > > I took that value from that section. > > The reason I think that there is an error in the SDM is that if you look > at the section 8.1.5, you'll see that bit 6 is a reserved bit. Thus, > does not make to set it on. > > I think the legit value ought to be 0x33F i.e. unset bit 6. Bit 6 is reserved, but it's forced to '1' by the CPU. Regardless, IMO it'd be better to drop this code entirely, it's all kinds of wonky. The label says "xsave_area" and implies XSAVE state is being loaded, but the code uses FXRSTOR, which will only load x86/MMX/XMM state, i.e. the first 512 bytes of the so called xsave_area. The test enclave doesn't touch state managed by XSAVE, let alone put secrets into said state. I see no reason to bother purging anything. > In any case check: > > https://raw.githubusercontent.com/jsakkine-intel/linux-sgx/master/tools/testing/selftests/x86/sgx/encl_bootstrap.S > > I.e. both have now a reference: > > 1. To the section that describes the default. > 2. To the section that describes what the bits mean. > > /Jarkko
