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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH v36 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call
Date:   Tue, 11 Aug 2020 08:16:54 -0700
Message-Id: <C107C4D3-1730-41BA-960C-C75B32DB43A0@amacapital.net>
References: <DD7996A6-CBA3-47CE-8DF2-9A6ADD3FE89E@amacapital.net>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Nathaniel McCallum <npmccallum@redhat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        X86 ML <x86@kernel.org>, linux-sgx@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Jethro Beekman <jethro@fortanix.com>,
        Cedric Xing <cedric.xing@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        asapek@google.com, Borislav Petkov <bp@alien8.de>,
        chenalexchen@google.com, Conrad Parker <conradparker@google.com>,
        cyhanish@google.com, Dave Hansen <dave.hansen@intel.com>,
        "Huang, Haitao" <haitao.huang@intel.com>,
        Josh Triplett <josh@joshtriplett.org>,
        "Huang, Kai" <kai.huang@intel.com>,
        "Svahn, Kai" <kai.svahn@intel.com>, Keith Moyer <kmoy@google.com>,
        Christian Ludloff <ludloff@google.com>,
        Neil Horman <nhorman@redhat.com>,
        Patrick Uiterwijk <puiterwijk@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Thomas Gleixner <tglx@linutronix.de>, yaozhangx@google.com
In-Reply-To: <DD7996A6-CBA3-47CE-8DF2-9A6ADD3FE89E@amacapital.net>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Aug 10, 2020, at 5:52 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>=20
> =EF=BB=BF
>>> On Aug 10, 2020, at 4:48 PM, Sean Christopherson <sean.j.christopherson@=
intel.com> wrote:
>>>=20
>>> =EF=BB=BFOn Mon, Aug 10, 2020 at 04:08:46PM -0700, Andy Lutomirski wrote=
:
>>> What am I missing?  I still don't really understand why we are
>>> supporting this mechanism at all.  Just the asm code to invoke the
>>> callback seems to be about half of the entire function.
>>=20
>> Because the Intel SDK (and other SDKs?) wants to use the host stack to pa=
ss
>> parameters out of the enclave.
>=20
> Ugh, right.  I forgot about that particular abomination.
>=20
> I suppose that passing a context pointer would be reasonable.

The alternative would be to pass in a parameter that gets put in RSP before e=
ntering the enclave. The idea is that the untrusted runtime would allocate a=
 couple pages with guard pages at either end, and enclaves using the regrett=
able arguments-on-the-stack scheme would end up using the alternative stack.=


At the end of the day, none of this really matters too much. Languages that c=
an do inline asm but can=E2=80=99t do container_of() can get fixed or use wo=
rkarounds.=