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SubjectRe: [RFC PATCH v2 0/3] An alternative __vdso_sgx_enter_enclave() to allow enclave/host parameter passing using untrusted stack
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?
2. How is it simpler approach? There is a strong claim of simplicity
and convenience without anything backing it.
3. Why we need both register and stack based approach co-exist? I'd go
with one approach for a new API without any legacy whatsoever.

This really needs a better pitch before we can consider doing anything
to it.

Also, in [2] there is talk about the next revision. Maybe the way go
forward is to address the three issues I found in the cover letter
and fix whatever needed to be fixed in the actual patches?

[1] https://lkml.org/lkml/2019/4/24/84
[2] https://lkml.org/lkml/2019/4/25/1170

/Jarkko

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