Re: [PATCH v14 09/19] x86/mm: x86/sgx: Signal SEGV_SGXERR for #PFs w/ PF_SGX

[Dave Hansen]

On 09/26/2018 02:15 PM, Andy Lutomirski wrote:
> Could we perhaps have a little vDSO entry (or syscall, I suppose) that
> runs an enclave an returns an error code, and rig up the #PF handler
> to check if the error happened in the vDSO entry and fix it up rather
> than sending a signal?

Yeah, signals suck.

So, instead of doing the enclave entry instruction (EENTER is it?), the
app would do the vDSO call.  It would have some calling convention, like
"set %rax to 0 before entering".  Then, we just teach the page fault
handler about the %RIP in the vDSO that can fault and how to move one
instruction later, munge %RIP to a value that tells about the error,
then return from the fault.  It would basically be like the kernel
exception tables, but for userspace.  Right?

How would a syscall work, though?  I assume we can't just enter the
enclave from ring0.