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Date:   Thu, 11 Jul 2019 12:36:21 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     "Xing, Cedric" <cedric.xing@intel.com>
Cc:     linux-kernel@vger.kernel.org, linux-sgx@vger.kernel.org,
        akpm@linux-foundation.org, dave.hansen@intel.com,
        sean.j.christopherson@intel.com, serge.ayoun@intel.com,
        shay.katz-zamir@intel.com, haitao.huang@intel.com,
        kai.svahn@intel.com, kai.huang@intel.com
Subject: Re: [RFC PATCH v2 0/3] An alternative __vdso_sgx_enter_enclave() to
 allow enclave/host parameter passing using untrusted stack
Message-ID: <20190711093621.4wstj7bc7w6wxxj2@linux.intel.com>
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 <686e47d2-f45c-6828-39d1-48374925de6c@intel.com>
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On Wed, Jul 10, 2019 at 03:54:20PM -0700, Xing, Cedric wrote:
> On 7/10/2019 3:46 PM, 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?
> 
> There is a lengthy discussion on its usefulness so I don't want to repeat.
> In short, it allows using untrusted stack as a convenient method to exchange
> data with the enclave. It is currently being used by Intel's SGX SDK for
> e/o-calls parameters.
> 
> > > 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.
> 
> Sure.
> 
> Any other questions I can help with?

I dissected my concerns in other email. We can merge this feature after
v21 if it makes sense.

/Jarkko