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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	X86 ML <x86@kernel.org>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-sgx@vger.kernel.org,
	Haitao Huang <haitao.huang@linux.intel.com>,
	Jethro Beekman <jethro@fortanix.com>,
	"Dr. Greg Wettstein" <greg@enjellic.com>
Subject: Re: [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU
Date: Tue, 11 Dec 2018 14:23:12 -0800	[thread overview]
Message-ID: <20181211222312.GI14731@linux.intel.com> (raw)
In-Reply-To: <CALCETrXOXh8Gb_d7NYLakx4w+JVEe79t11wFPLpy+5MEq9kq=A@mail.gmail.com>

On Tue, Dec 11, 2018 at 09:58:19AM -0800, Andy Lutomirski wrote:
> > On Dec 11, 2018, at 8:52 AM, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> >
> >> On Tue, Dec 11, 2018 at 07:41:27AM -0800, Andy Lutomirski wrote:
> >>
> >>
> >>>> On Dec 10, 2018, at 3:24 PM, Josh Triplett <josh@joshtriplett.org> wrote:
> >>>>
> >>>> On Mon, Dec 10, 2018 at 03:21:37PM -0800, Sean Christopherson wrote:
> >>>> At that point I realized it's a hell of a lot easier to simply provide
> >>>> an IOCTL via /dev/sgx that allows userspace to register a per-process
> >>>> ENCLU exception handler.  At a high level, the basic idea is the same
> >>>> as the vDSO approach: provide a hardcoded fixup handler for ENCLU and
> >>>> attempt to fixup select unhandled exceptions that occurred in user code.
> >>>
> >>> So, on the one hand, this is *absolutely* much cleaner than the VDSO
> >>> approach. On the other hand, this is global process state and has some
> >>> of the same problems as a signal handler as a result.
> >>
> >> I liked the old version better for this reason
> >
> > This isn't fundamentally different than forcing all EENTER calls through
> > the vDSO, which is also per-process.  Technically this is more flexible
> > in that regard since userspace gets to choose where their one ENCLU gets
> > to reside.  Userspace can have per-enclave entry flows so long as the
> > actual ENLU[EENTER] is common, same as vDSO.
> 
> Right. The problem is that user libraries have a remarkably hard time
> agreeing on where their one copy of anything lives.

Are you concerned about userspace shooting themselves in the foot, e.g.
unknowingly overwriting their handler?  Requiring unregister->register
to change the handler would mitigate that issue for the most part.  Or
we could even say it's a write-once property.

That obviously doesn't solve the issue of a userspace application
deliberately using two different libraries to run enclaves in a single
process, but I have a hard time envisioning a scenario where someone
would want to use two different *SGX* libraries in a single process.
Don't most of the signal issue arise due to loading multiple libraries
that provide *different* services needing to handle signals?

  parent reply	other threads:[~2018-12-11 22:23 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-10 23:21 [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU Sean Christopherson
2018-12-10 23:21 ` [RFC PATCH v3 1/4] x86/sgx: Add a per-mm ENCLU exception fixup handler Sean Christopherson
2018-12-10 23:21 ` [RFC PATCH v3 2/4] x86/fault: Attempt to fixup unhandled #PF on ENCLU before signaling Sean Christopherson
2018-12-10 23:21 ` [RFC PATCH v3 3/4] x86/traps: Attempt to fixup exceptions in vDSO " Sean Christopherson
2018-12-10 23:21 ` [RFC PATCH v3 4/4] x86/sgx: Add an SGX IOCTL to register a per-mm ENCLU exception handler Sean Christopherson
2018-12-10 23:24 ` [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU Josh Triplett
2018-12-11 14:53   ` Dr. Greg
2018-12-11 15:01     ` Sean Christopherson
2018-12-11 15:41   ` Andy Lutomirski
2018-12-11 16:52     ` Sean Christopherson
2018-12-11 17:58       ` Andy Lutomirski
2018-12-11 18:40         ` Sean Christopherson
2018-12-11 22:23         ` Sean Christopherson [this message]
2018-12-11 23:10           ` Andy Lutomirski
2018-12-11 23:29             ` Sean Christopherson
2018-12-12  2:42             ` Dr. Greg

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