linux-kernel - Re: [PATCH v36 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call

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Date:   Wed, 19 Aug 2020 17:19:42 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Nathaniel McCallum <npmccallum@...hat.com>,
        X86 ML <x86@...nel.org>, linux-sgx@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jethro Beekman <jethro@...tanix.com>,
        Cedric Xing <cedric.xing@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        asapek@...gle.com, Borislav Petkov <bp@...en8.de>,
        chenalexchen@...gle.com, Conrad Parker <conradparker@...gle.com>,
        cyhanish@...gle.com, Dave Hansen <dave.hansen@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        Josh Triplett <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        "Svahn, Kai" <kai.svahn@...el.com>, Keith Moyer <kmoy@...gle.com>,
        Christian Ludloff <ludloff@...gle.com>,
        Neil Horman <nhorman@...hat.com>,
        Patrick Uiterwijk <puiterwijk@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, yaozhangx@...gle.com
Subject: Re: [PATCH v36 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call

On Tue, Aug 18, 2020 at 8:15 AM Jarkko Sakkinen
<jarkko.sakkinen@...ux.intel.com> wrote:
>
> 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@...hat.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?

The same as now.  The enclave would see a pointer to a stack-like
writable area in USER_RSP, but it just wouldn't be the actual stack.

I suppose that the caller of the vdso can play these games just as
well as the vdso itself, though, so maybe this is not helpful.

--Andy