+Cc: linux-sgx, Haitao, Greg and Jethro My apologies for neglecting to cc the SGX folks, original thread is here: https://lkml.kernel.org/r/20181206221922.31012-1-sean.j.christopherson@xxxxxxxxx On Thu, Dec 06, 2018 at 02:50:01PM -0800, Andy Lutomirski wrote: > On Thu, Dec 6, 2018 at 2:19 PM Sean Christopherson > <sean.j.christopherson@xxxxxxxxx> wrote: > > > + > > + /* > > + * Invoke the caller's exit handler if one was provided. The return > > + * value tells us whether to re-enter the enclave (EENTER or ERESUME) > > + * or to return (EEXIT). > > + */ > > + if (exit_handler) { > > + leaf = exit_handler(exit_info, tcs, priv); > > + if (leaf == SGX_EENTER || leaf == SGX_ERESUME) > > + goto enter_enclave; > > + if (leaf == SGX_EEXIT) > > + return 0; > > + return -EINVAL; > > + } else if (leaf != SGX_EEXIT) { > > + return -EFAULT; > > + } > > This still seems overcomplicated to me. How about letting the > requested leaf (EENTER or ERESUME) be a parameter to the function and > then just returning here? As it stands, you're requiring any ERESUME > that gets issued (other than the implicit ones) to be issued in the > same call stack, which is very awkward if you're doing something like > forwarding the fault to a different task over a socket and then > waiting in epoll_wait() or similar before resuming the enclave. Ah, yeah, wasn't thinking about usage models where the enclave could get passed off to a different thread. What about supporting both, i.e. keep the exit handler but make it 100% optional? And simplify the exit_handler to effectively return a boolean, i.e. "exit or continue". Something like this: notrace long __vdso_sgx_enter_enclave(u32 op, void *tcs, void *priv, struct sgx_enclave_exit_info *exit_info, sgx_enclave_exit_handler *exit_handler) { u64 rdi, rsi, rdx; u32 leaf; long ret; if (!tcs || !exit_info) return -EINVAL; enter_enclave: if (op != SGX_EENTER && op != SGX_ERESUME) return -EINVAL; <same core code> /* * Invoke the caller's exit handler if one was provided. The return * value tells us whether to re-enter the enclave (EENTER or ERESUME) * or to return (EEXIT). */ if (exit_handler) { if (exit_handler(exit_info, tcs, priv)) { op = exit_info->leaf; goto enter_enclave; } } if (exit_info->leaf == SGX_EEXIT) return -EFAULT; return 0; } I like that the exit handler allows userspace to trap/panic with the full call stack in place, and in a dedicated path, i.e. outside of the basic enter/exit code. An exit handler probably doesn't fundamentally change what userspace can do with respect to debugging/reporting, but I think it would actually simplify some userspace implementations, e.g. I'd use it in my tests like so: long fault_handler(struct sgx_enclave_exit_info *exit_info, void *tcs, void *priv) { if (exit_info->leaf == SGX_EEXIT) return 0; <report exception and die/hang> }
