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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Andy Lutomirski <luto@amacapital.net>, q@linux.intel.com
Cc: "Xing, Cedric" <cedric.xing@intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	James Morris <jmorris@namei.org>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	LSM List <linux-security-module@vger.kernel.org>,
	Paul Moore <paul@paul-moore.com>,
	Eric Paris <eparis@parisplace.org>,
	"selinux@vger.kernel.org" <selinux@vger.kernel.org>,
	Jethro Beekman <jethro@fortanix.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	"linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"nhorman@redhat.com" <nhorman@redhat.com>,
	"npmccallum@redhat.com" <npmccallum@redhat.com>,
	"Ayoun, Serge" <serge.ayoun@intel.com>,
	"Katz-zamir, Shay" <shay.katz-zamir@intel.com>,
	"Huang, Haitao" <haitao.huang@intel.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	"Svahn, Kai" <kai.svahn@intel.com>,
	Borislav Petkov <bp@alien8.de>,
	Josh Triplett <josh@joshtriplett.org>,
	"Huang, Kai" <kai.huang@intel.com>,
	David Rientjes <rientjes@google.com>,
	"Roberts, William C" <william.c.roberts@intel.com>,
	"Tricca, Philip B" <philip.b.tricca@intel.com>
Subject: Re: [RFC PATCH v2 2/5] x86/sgx: Require userspace to define enclave pages' protection bits
Date: Wed, 12 Jun 2019 07:34:05 -0700
Message-ID: <20190612143405.GC20308@linux.intel.com> (raw)
In-Reply-To: <331B31BF-9892-4FB3-9265-3E37412F80F4@amacapital.net>

On Tue, Jun 11, 2019 at 05:09:28PM -0700, Andy Lutomirski wrote:
> 
> On Jun 10, 2019, at 3:28 PM, Xing, Cedric <cedric.xing@intel.com> wrote:
> 
> >> From: Andy Lutomirski [mailto:luto@kernel.org]
> >> Sent: Monday, June 10, 2019 12:15 PM
> >> This seems like an odd workflow.  Shouldn't the #PF return back to
> >> untrusted userspace so that the untrusted user code can make its own
> >> decision as to whether it wants to EAUG a page there as opposed to, say,
> >> killing the enclave or waiting to keep resource usage under control?
> > 
> > This may seem odd to some at the first glance. But if you can think of how
> > static heap (pre-allocated by EADD before EINIT) works, the load parses the
> > "metadata" coming with the enclave to decide the address/size of the heap,
> > EADDs it, and calls it done. In the case of "dynamic" heap (allocated
> > dynamically by EAUG after EINIT), the same thing applies - the loader
> > determines the range of the heap, tells the SGX module about it, and calls
> > it done. Everything else is the between the enclave and the SGX module.
> > 
> > In practice, untrusted code usually doesn't know much about enclaves, just
> > like it doesn't know much about the shared objects loaded into its address
> > space either. Without the necessary knowledge, untrusted code usually just
> > does what it is told (via o-calls, or return value from e-calls), without
> > judging that's right or wrong. 
> > 
> > When it comes to #PF like what I described, of course a signal could be
> > sent to the untrusted code but what would it do then? Usually it'd just
> > come back asking for a page at the fault address. So we figured it'd be
> > more efficient to just have the kernel EAUG at #PF. 
> > 
> > Please don't get me wrong though, as I'm not dictating what the s/w flow
> > shall be. It's just going to be a choice offered to user mode. And that
> > choice was planned to be offered via mprotect() - i.e. a writable vma
> > causes kernel to EAUG while a non-writable vma will result in a signal
> > (then the user mode could decide whether to EAUG). The key point is
> > flexibility - as we want to allow all reasonable s/w flows instead of
> > dictating one over others. We had similar discussions on vDSO API before.
> > And I think you accepted my approach because of its flexibility. Am I
> > right?
> 
> As long as user code can turn this off, I have no real objection. But it
> might make sense to have it be more explicit — have an ioctl set up a range
> as “EAUG-on-demand”.

This was part of the motivation behind changing SGX_IOC_ENCLAVE_ADD_PAGE
to SGX_IOC_ENCLAVE_ADD_REGION and adding a @flags parameter.  E.g. adding
support for "EAUG-on-demand" regions would just be a new flag.

> But this is all currently irrelevant. We can argue about it when the patches
> show up. :)

  reply index

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-06  2:11 [RFC PATCH v2 0/5] security: x86/sgx: SGX vs. LSM Sean Christopherson
2019-06-06  2:11 ` [RFC PATCH v2 1/5] mm: Introduce vm_ops->may_mprotect() Sean Christopherson
2019-06-10 15:06   ` Jarkko Sakkinen
2019-06-10 15:55     ` Sean Christopherson
2019-06-10 17:47       ` Xing, Cedric
2019-06-10 19:49         ` Sean Christopherson
2019-06-10 22:06           ` Xing, Cedric
2019-06-06  2:11 ` [RFC PATCH v2 2/5] x86/sgx: Require userspace to define enclave pages' protection bits Sean Christopherson
2019-06-10 15:27   ` Jarkko Sakkinen
2019-06-10 16:15     ` Sean Christopherson
2019-06-10 17:45       ` Jarkko Sakkinen
2019-06-10 18:17         ` Sean Christopherson
2019-06-12 19:26           ` Jarkko Sakkinen
2019-06-10 18:29   ` Xing, Cedric
2019-06-10 19:15     ` Andy Lutomirski
2019-06-10 22:28       ` Xing, Cedric
2019-06-12  0:09         ` Andy Lutomirski
2019-06-12 14:34           ` Sean Christopherson [this message]
2019-06-12 18:20             ` Xing, Cedric
2019-06-06  2:11 ` [RFC PATCH v2 3/5] x86/sgx: Enforce noexec filesystem restriction for enclaves Sean Christopherson
2019-06-10 16:00   ` Jarkko Sakkinen
2019-06-10 16:44     ` Andy Lutomirski
2019-06-11 17:21       ` Stephen Smalley
2019-06-06  2:11 ` [RFC PATCH v2 4/5] LSM: x86/sgx: Introduce ->enclave_load() hook for Intel SGX Sean Christopherson
2019-06-07 19:58   ` Stephen Smalley
2019-06-10 16:21     ` Sean Christopherson
2019-06-10 16:05   ` Jarkko Sakkinen
2019-06-06  2:11 ` [RFC PATCH v2 5/5] security/selinux: Add enclave_load() implementation Sean Christopherson
2019-06-07 21:16   ` Stephen Smalley
2019-06-10 16:46     ` Sean Christopherson
2019-06-17 16:38   ` Jarkko Sakkinen
2019-06-10  7:03 ` [RFC PATCH v1 0/3] security/x86/sgx: SGX specific LSM hooks Cedric Xing
2019-06-10  7:03   ` [RFC PATCH v1 1/3] LSM/x86/sgx: Add " Cedric Xing
2019-06-10  7:03   ` [RFC PATCH v1 2/3] LSM/x86/sgx: Implement SGX specific hooks in SELinux Cedric Xing
2019-06-11 13:40     ` Stephen Smalley
2019-06-11 22:02       ` Sean Christopherson
2019-06-12  9:32         ` Dr. Greg
2019-06-12 14:25           ` Sean Christopherson
2019-06-13  7:25             ` Dr. Greg
2019-06-12 19:30         ` Andy Lutomirski
2019-06-12 22:02           ` Sean Christopherson
2019-06-13  0:10             ` Xing, Cedric
2019-06-13  1:02             ` Xing, Cedric
2019-06-13 17:02         ` Stephen Smalley
2019-06-13 23:03           ` Xing, Cedric
2019-06-13 23:17             ` Sean Christopherson
2019-06-14  0:31               ` Xing, Cedric
2019-06-14  0:46           ` Sean Christopherson
2019-06-14 15:38             ` Sean Christopherson
2019-06-16 22:14               ` Andy Lutomirski
2019-06-17 16:49                 ` Sean Christopherson
2019-06-17 17:08                   ` Andy Lutomirski
2019-06-18 15:40                   ` Dr. Greg
2019-06-14 17:16             ` Xing, Cedric
2019-06-14 17:45               ` Sean Christopherson
2019-06-14 17:53                 ` Sean Christopherson
2019-06-14 20:01                   ` Sean Christopherson
2019-06-16 22:16               ` Andy Lutomirski
2019-06-14 23:19             ` Dr. Greg
2019-06-11 22:55       ` Xing, Cedric
2019-06-13 18:00         ` Stephen Smalley
2019-06-13 19:48           ` Sean Christopherson
2019-06-13 21:09             ` Xing, Cedric
2019-06-13 21:02           ` Xing, Cedric
2019-06-14  0:37           ` Sean Christopherson
2019-06-10  7:03   ` [RFC PATCH v1 3/3] LSM/x86/sgx: Call new LSM hooks from SGX subsystem Cedric Xing
2019-06-10 17:36   ` [RFC PATCH v1 0/3] security/x86/sgx: SGX specific LSM hooks Jarkko Sakkinen

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