Hi Andy, > From: linux-sgx-owner@xxxxxxxxxxxxxxx [mailto:linux-sgx- > owner@xxxxxxxxxxxxxxx] On Behalf Of Andy Lutomirski > > I suppose the real question is: are there a significant number of > users who will want to run enclaves created using an old SDK on Linux? > And will there actually be support for doing this in the software > stack? To your first question, I cannot share information of Intel customers or speak for them. But in general, people would like to stay with an old enclave usually because of: 1) attestation, because MRENCLAVE will change after rebuild; and/or 2) the need to support a mix of older and newer Linux kernels. So I'd say it'll be commonly desired, especially when this vDSO API is still "new" (so not available on every platform). To your second question, Intel will support all "legacy" enclaves built with older SGX SDKs on newer kernels. And that's why we are so eager to find a migration path. I can't speak for other companies, but guess backward compatibility is always desirable. > > If the answer to both questions is yes, then it seems like it could be > reasonable to support it in the vDSO. But I still think it should > probably be a different vDSO entry point so that the normal case > doesn't become more complicated. I'll support whatever you think is more appropriate. At the end, I'd like to give out the full version of my proposal, with your feedbacks (i.e. stack unwinder and Spectre variant 2) addressed. I'm a bit concerned by retpoline, which won't work (or be needed) when CET comes online. Are you looking to change it again then? Here's the summary of the changes: - Added CFI directives for proper unwinding. - Defined sgx_ex_callback - the callback function on enclave exit/exception. - Aligned stack properly before calling sgx_ex_callback (per x86_64 ABI). - Used retpoline in place of indirect call. - The block starting at label "4:" captures all the code necessary to support sgx_ex_call. It has grown longer due to retpoline. /** * __vdso_sgx_enter_enclave() - Enter an SGX enclave * * %eax: ENCLU leaf, must be either EENTER or ERESUME * 0x08(%rsp): TCS * 0x10(%rsp): Optional pointer to 'struct sgx_enclave_exception' * 0x18(%rsp): Optional function pointer to 'sgx_ex_callback', whose * definition will be given below. Note that this function, if * present, shall follow x86_64 ABI. * return: 0 (zero) on success, or a negative error code on failure. * * Note that __vdso_sgx_enter_enclave() is not compatible with x86_64 ABI. * All registers except RBP must be treated as volatile from the caller's * perspective, including but not limited to GPRs, EFLAGS.DF, MXCSR, FCW, etc... * Enclave may decrement RSP, but must not increment it - i.e. existing content * of the stack shall be preserved. * * sgx_ex_callback - A callback function to be invoked by * __vdso_sgx_enter_enclave() upon exception or after the enclave exits. * * typedef int (*sgx_ex_callback)(long rdi, long rsi, long rdx, * struct sgx_enclave_exception *ex_info, long r8, long r9, * long rsp, void *tcs); * * Note that sgx_ex_callback shall be x86_64 ABI compliant. * * Note that other GPRs (except %rax, %rbx and %rcx) are also passed through to * sgx_ex_callback, even though accessing them requires assembly code. */ __vdso_sgx_enter_enclave: /* prolog */ .cfi_startproc push %rbp .cfi_adjust_cfa_offset 8 .cfi_rel_offset %rbp, 0 mov %rsp, %rbp .cfi_def_cfa_register %rbp 1: /* EENTER <= leaf <= ERESUME */ cmp $0x2, %eax jb 5f cmp $0x3, %eax ja 5f /* Load TCS and AEP */ mov 0x10(%rbp), %rbx lea 2f(%rip), %rcx 2: enclu /* EEXIT path */ mov 0x18(%rbp), %rcx jrcxz 3f mov %eax, EX_LEAF(%rcx) /* normalize return value */ 3: xor %eax, %eax 4: /* call sgx_ex_callback if supplied */ cmpq $0, 0x20(%rbp) jz 6f /* align stack per x86_64 ABI */ mov %rsp, %rbx and $-0x10, %rsp /* parameters */ push 0x10(%rbp) push %rbx /* call *0x20(%rbp) using retpoline */ mov 0x20(%rbp), %rax call 41f /* stack cleanup */ mov %rbx, %rsp jmp 1b 41: call 43f 42: pause lfence jmp 42b 43: mov %rax, (%rsp) ret 5: /* bad leaf */ cmp $0, %eax jle 6f mov $(-EINVAL), %eax 6: /* epilog */ leave .cfi_def_cfa %rsp, 8 ret .cfi_endproc .pushsection .fixup, "ax" 7: mov 0x18(%rbp), %rcx jrcxz 8f /* fill in ex_info */ mov %eax, EX_LEAF(%rcx) mov %di, EX_TRAPNR(%rcx) mov %si, EX_ERROR_CODE(%rcx) mov %rdx, EX_ADDRESS(%rcx) 8: mov $(-EFAULT), %eax jmp 4b .popsection _ASM_VDSO_EXTABLE_HANDLE(2b, 7b) -Cedric
