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Date:   Tue, 18 Aug 2020 18:15:24 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     Nathaniel McCallum <npmccallum@redhat.com>,
        X86 ML <x86@kernel.org>, linux-sgx@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        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
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On Mon, Aug 10, 2020 at 04:08:46PM -0700, Andy Lutomirski wrote:
> On Thu, Aug 6, 2020 at 7:55 AM Nathaniel McCallum <npmccallum@redhat.com> wrote:
> >
> > In a past revision of this patch, I had requested a void *misc
> > parameter that could be passed through vdso_sgx_enter_enclave_t into
> > sgx_enclave_exit_handler_t. This request encountered some push back
> > and I dropped the issue. However, I'd like to revisit it or something
> > similar.
> 
> Why do you need an exit handler at all?  IIRC way back when I
> suggested that we simply not support it at all.  If you want to
> call__vdso_sgx_enter_enclave() in a loop, call it in a loop.  If you
> want to wrap it intelligently in Rust, you don't want a callback
> anyway -- that forces you have an FFI (or non-Rust, anyway) frame on
> the stack, which interacts poorly with panic handling and prevents you
> from using await in your Rust callback handler.  If, on the other
> hand, you just call __vdso_sg_enter_enclave() in a loop, all these
> problems go away and, if you really want, you can pass in a callback
> in Rust and call the callback from Rust.

How would Intel SDK be able to do its stack manipulation?

> 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.

I'm most worried maintaining all of this given all the innovative ways
that users can exploit an uapi.

/Jarkko