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

From: Andy Lutomirski <luto@kernel.org>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	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
Date: Wed, 19 Aug 2020 17:19:42 -0700	[thread overview]
Message-ID: <CALCETrWHfL6_BOuVAi=ucB8N=pQiWV_dF3YpWndEq5LWaUD9tw@mail.gmail.com> (raw)
In-Reply-To: <20200818151524.GE132200@linux.intel.com>

On Tue, Aug 18, 2020 at 8:15 AM Jarkko Sakkinen
<jarkko.sakkinen@linux.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@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?

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