Re: [PATCH v36 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call

[Jarkko Sakkinen]

On Mon, Aug 10, 2020 at 04:08:46PM -0700, Andy Lutomirski wrote:
> On Thu, Aug 6, 2020 at 7:55 AM Nathaniel McCallum <npmccallum@xxxxxxxxxx> wrote:
> >
> > In a past revision of this patch, I had requested a void *misc
> > parameter that could be passed through vdso_sgx_enter_enclave_t into
> > sgx_enclave_exit_handler_t. This request encountered some push back
> > and I dropped the issue. However, I'd like to revisit it or something
> > similar.
> 
> Why do you need an exit handler at all?  IIRC way back when I
> suggested that we simply not support it at all.  If you want to
> call__vdso_sgx_enter_enclave() in a loop, call it in a loop.  If you
> want to wrap it intelligently in Rust, you don't want a callback
> anyway -- that forces you have an FFI (or non-Rust, anyway) frame on
> the stack, which interacts poorly with panic handling and prevents you
> from using await in your Rust callback handler.  If, on the other
> hand, you just call __vdso_sg_enter_enclave() in a loop, all these
> problems go away and, if you really want, you can pass in a callback
> in Rust and call the callback from Rust.

How would Intel SDK be able to do its stack manipulation?

> What am I missing?  I still don't really understand why we are
> supporting this mechanism at all.  Just the asm code to invoke the
> callback seems to be about half of the entire function.

I'm most worried maintaining all of this given all the innovative ways
that users can exploit an uapi.

/Jarkko