On Fri, Dec 7, 2018 at 8:51 AM Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > +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> > } > Hmm. That't not totally silly, although you could accomplish almost the same thing by wrapping the vDSO helper in another function.
