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From: "Xing, Cedric" <cedric.xing@intel.com>
To: "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
	"Stephen Smalley" <sds@tycho.nsa.gov>
Cc: "linux-security-module@vger.kernel.org" 
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	"Ayoun, Serge" <serge.ayoun@intel.com>,
	"Katz-zamir, Shay" <shay.katz-zamir@intel.com>,
	"Huang, Haitao" <haitao.huang@intel.com>,
	"andriy.shevchenko@linux.intel.com" 
	<andriy.shevchenko@linux.intel.com>,
	"Svahn, Kai" <kai.svahn@intel.com>, "bp@alien8.de" <bp@alien8.de>,
	"josh@joshtriplett.org" <josh@joshtriplett.org>,
	"Huang, Kai" <kai.huang@intel.com>,
	"rientjes@google.com" <rientjes@google.com>,
	"Roberts, William C" <william.c.roberts@intel.com>,
	"Tricca, Philip B" <philip.b.tricca@intel.com>
Subject: RE: [RFC PATCH v1 2/3] LSM/x86/sgx: Implement SGX specific hooks in SELinux
Date: Fri, 14 Jun 2019 17:16:55 +0000
Message-ID: <960B34DE67B9E140824F1DCDEC400C0F65504665@ORSMSX116.amr.corp.intel.com> (raw)
In-Reply-To: <20190614004600.GF18385@linux.intel.com>

> From: Christopherson, Sean J
> Sent: Thursday, June 13, 2019 5:46 PM
> 
> On Thu, Jun 13, 2019 at 01:02:17PM -0400, Stephen Smalley wrote:
> > On 6/11/19 6:02 PM, Sean Christopherson wrote:
> > >On Tue, Jun 11, 2019 at 09:40:25AM -0400, Stephen Smalley wrote:
> > >>I haven't looked at this code closely, but it feels like a lot of
> > >>SGX-specific logic embedded into SELinux that will have to be
> > >>repeated or reused for every security module.  Does SGX not track
> this state itself?
> > >
> > >SGX does track equivalent state.
> > >
> > >There are three proposals on the table (I think):
> > >
> > >   1. Require userspace to explicitly specificy (maximal) enclave
> page
> > >      permissions at build time.  The enclave page permissions are
> provided
> > >      to, and checked by, LSMs at enclave build time.
> > >
> > >      Pros: Low-complexity kernel implementation, straightforward
> auditing
> > >      Cons: Sullies the SGX UAPI to some extent, may increase
> complexity of
> > >            SGX2 enclave loaders.
> > >
> > >   2. Pre-check LSM permissions and dynamically track mappings to
> enclave
> > >      pages, e.g. add an SGX mprotect() hook to restrict W->X and WX
> > >      based on the pre-checked permissions.
> > >
> > >      Pros: Does not impact SGX UAPI, medium kernel complexity
> > >      Cons: Auditing is complex/weird, requires taking enclave-
> specific
> > >            lock during mprotect() to query/update tracking.
> > >
> > >   3. Implement LSM hooks in SGX to allow LSMs to track enclave
> regions
> > >      from cradle to grave, but otherwise defer everything to LSMs.
> > >
> > >      Pros: Does not impact SGX UAPI, maximum flexibility, precise
> auditing
> > >      Cons: Most complex and "heaviest" kernel implementation of the
> three,
> > >            pushes more SGX details into LSMs.
> > >
> > >My RFC series[1] implements #1.  My understanding is that Andy
> > >(Lutomirski) prefers #2.  Cedric's RFC series implements #3.
> > >
> > >Perhaps the easiest way to make forward progress is to rule out the
> > >options we absolutely *don't* want by focusing on the potentially
> > >blocking issue with each option:
> > >
> > >   #1 - SGX UAPI funkiness
> > >
> > >   #2 - Auditing complexity, potential enclave lock contention
> > >
> > >   #3 - Pushing SGX details into LSMs and complexity of kernel
> > > implementation
> > >
> > >
> > >[1]
> > >https://lkml.kernel.org/r/20190606021145.12604-1-sean.j.christopherso
> > >n@intel.com
> >
> > Given the complexity tradeoff, what is the clear motivating example
> > for why
> > #1 isn't the obvious choice? That the enclave loader has no way of
> > knowing a priori whether the enclave will require W->X or WX?  But
> > aren't we better off requiring enclaves to be explicitly marked as
> > needing such so that we can make a more informed decision about
> > whether to load them in the first place?
> 
> Andy and/or Cedric, can you please weigh in with a concrete (and
> practical) use case that will break if we go with #1?  The auditing
> issues for #2/#3 are complex to say the least...

How does enclave loader provide per-page ALLOW_* flags? And a related question is why they are necessary for enclaves but unnecessary for regular executables or shared objects.

What's the story for SGX2 if mmap()'ing non-existing pages is not allowed?

What's the story for auditing?

After everything above has been taken care of properly, will #1 still be simpler than #2/#3?


  parent reply index

Thread overview: 66+ 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
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
2019-06-14 17:16             ` Xing, Cedric [this message]
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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