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Date:   Thu, 13 Aug 2020 12:38:42 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Andy Lutomirski <luto@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
Subject: Re: [PATCH v36 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call
Message-ID: <20200813193842.GV29439@linux.intel.com>
References: <DD7996A6-CBA3-47CE-8DF2-9A6ADD3FE89E@amacapital.net>
 <C107C4D3-1730-41BA-960C-C75B32DB43A0@amacapital.net>
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On Tue, Aug 11, 2020 at 08:16:54AM -0700, Andy Lutomirski wrote:
> 
> > On Aug 10, 2020, at 5:52 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> > 
> > ﻿
> >>> On Aug 10, 2020, at 4:48 PM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> >>> 
> >>> ﻿On 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.
> >> 
> >> Because the Intel SDK (and other SDKs?) wants to use the host stack to pass
> >> parameters out of the enclave.
> > 
> > Ugh, right.  I forgot about that particular abomination.
> > 
> > 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
> entering the enclave. The idea is that the untrusted runtime would allocate a
> couple pages with guard pages at either end, and enclaves using the
> regrettable 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
> can do inline asm but can’t do container_of() can get fixed or use
> workarounds.

So, is your "official" opinion

   Go update the vDSO to allow passing an arbitrary pointer.

or

   Eh, don't bother.