Re: [RFC PATCH v2 0/3] An alternative __vdso_sgx_enter_enclave() to allow enclave/host parameter passing using untrusted stack

[Xing, Cedric]

On 7/11/2019 2:38 AM, Jarkko Sakkinen wrote:
> On Wed, Jul 10, 2019 at 04:37:41PM -0700, Xing, Cedric wrote:
> > On 7/10/2019 4:15 PM, Jarkko Sakkinen wrote:
> > > On Thu, Jul 11, 2019 at 01:46:28AM +0300, Jarkko Sakkinen wrote:
> > > > On Wed, Jul 10, 2019 at 11:08:37AM -0700, Xing, Cedric wrote:
> > > > > > With these conclusions I think the current vDSO API is sufficient for
> > > > > > Linux.
> > > > >
> > > > > The new vDSO API is to support data exchange on stack. It has nothing to do
> > > > > with debugging. BTW, the community has closed on this.
> > > >
> > > > And how that is useful?
> > > >
> > > > > The CFI directives are for stack unwinding. They don't affect what the code
> > > > > does so you can just treat them as NOPs if you don't understand what they
> > > > > do. However, they are useful to not only debuggers but also exception
> > > > > handling code. libunwind also has a setjmp()/longjmp() implementation based
> > > > > on CFI directives.
> > > >
> > > > Of course I won't merge code of which usefulness I don't understand.
> > >
> > > I re-read the cover letter [1] because it usually is the place
> > > to "pitch" a feature.
> > >
> > > It fails to address two things:
> > >
> > > 1. How and in what circumstances is an untrusted stack is a better
> > >      vessel for handling exceptions than the register based approach
> > >      that we already have?
> >
> > We are not judging which vessel is better (or the best) among all possible
> > vessels. We are trying to enable more vessels. Every vessel has its pros and
> > cons so there's *no* single best vessel.
>
> I think reasonable metric is actually the coverage of the Intel SDK
> based enclaves. How widely are they in the wild? If the user base is
> large, it should be reasonable to support this just based on that.

I don't know how many existing enclaves out there, but definitely larger 
than 0 (zero), while user base for the old API is definitely 0. What are 
you worrying, really?

> /Jarkko