linux-kernel - RE: [PATCH v19,RESEND 24/27] x86/vdso: Add __vdso_sgx_enter_enclave() to wrap SGX enclave transitions

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Message-ID: <960B34DE67B9E140824F1DCDEC400C0F4E85C567@ORSMSX116.amr.corp.intel.com>
Date:   Wed, 20 Mar 2019 20:10:53 +0000
From:   "Xing, Cedric" <cedric.xing@...el.com>
To:     Jethro Beekman <jethro@...tanix.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "Katz-zamir, Shay" <shay.katz-zamir@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Svahn, Kai" <kai.svahn@...el.com>, "bp@...en8.de" <bp@...en8.de>,
        "josh@...htriplett.org" <josh@...htriplett.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        "rientjes@...gle.com" <rientjes@...gle.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Haitao Huang" <haitao.huang@...ux.intel.com>,
        "Dr . Greg Wettstein" <greg@...ellic.com>
Subject: RE: [PATCH v19,RESEND 24/27] x86/vdso: Add
 __vdso_sgx_enter_enclave() to wrap SGX enclave transitions

> > By requiring preservation of RSP at both AEX and EEXIT, this precludes
> the possibility of using the untrusted stack as temporary storage by
> enclaves. While that looks reasonable at first glance, I'm afraid it
> isn't the case in reality. The untrusted stack is inarguably the most
> convenient way for data exchange between an enclave and its enclosing
> process, and is in fact being used for that purpose by almost all
> existing enclaves to date. Given the expectation that this API will be
> used by all future SGX application, it looks unwise to ban the most
> convenient and commonly used approach for data exchange.
> 
> For reference, here's the code in the Intel toolchain responsible for
> this:
> https://github.com/intel/linux-
> sgx/blob/6a0b5ac71f8d16f04e0376f3b2168e80c773dd23/sdk/trts/trts.cpp#L125
> -L140
> 
> Regarding "almost all existing enclaves to date", enclaves built with
> the Fortanix toolchain don't touch the untrusted stack.
> 
> --
> Jethro Beekman | Fortanix

Thanks for providing the references. Yes, not every enclave touches the untrusted stack so I used the word "almost".

Everything exists for a reason. By bringing up what is done today, I was trying to inspire thinking on the more important question of "why is it done this way today?".