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

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Date:   Wed, 10 Jul 2019 15:54:20 -0700
From:   "Xing, Cedric" <cedric.xing@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        akpm@...ux-foundation.org, dave.hansen@...el.com,
        sean.j.christopherson@...el.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, haitao.huang@...el.com,
        kai.svahn@...el.com, kai.huang@...el.com
Subject: Re: [RFC PATCH v2 0/3] An alternative __vdso_sgx_enter_enclave() to
 allow enclave/host parameter passing using untrusted stack

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?

> /Jarkko
>